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A developmental switch sufficient for flower initiation in diverse plants
Abstract
We have generated transgenic plants in which the flower-meristem-identity gene LEAFY of Arabidopsis is constitutively expressed. LEAFY is sufficient to determine floral fate in lateral shoot meristems of both Arabidopsis and the heterologous species aspen, with the consequence that flower development is induced precociously. Our results also suggest a new level of regulation during flower development, as indicated by the competence of the main shoot to respond to LEAFY activity.
... Therefore, it has been suggested that flowering-time genes regulate flowering by either activating LFY expression or modulating the response to LFY. Consistently, LFY expression is activated by the transition to flowering, and constitutive expression of LFY or AP1 causes early flowering (Mandel and Yanofsky 1995;Weigel and Nilsson 1995;Blá zquez et al. 1997). ...
... An important regulator of the transition from secondary shoots to flowers is the LFY transcription factor (Weigel and Nilsson 1995). Therefore, we monitored LFY expression levels in agl20-101D FRI FLC using a LFY::GUS fusion gene (Blá zquez et al. 1997). ...
... Interestingly, both lines showed solitary flowers in the axils of cauline leaves (Fig. 1H,I). Such a con-version of secondary shoots to flowers is also observed in 35S::LFY or 35S::AP1 plants (Mandel and Yanofsky 1995;Weigel and Nilsson 1995). This result may indicate that AGL20 overexpression can activate flower meristem identity genes such as LFY or AP1 in shoot meristems, once FRI FLC is removed. ...
The very late-flowering behavior of Arabidopsis winter-annual ecotypes is conferred mainly by two genes, FRIGIDA (FRI) and FLOWERING LOCUS C (FLC). A MADS-domain gene, AGAMOUS-LIKE 20 (AGL20), was identified as a dominant FRI suppressor in activation tagging mutagenesis. Overexpression of AGL20 suppresses not only the late flowering of plants that have functional FRI and FLC alleles but also the delayed phase transitions during the vegetative stages of plant development. Interestingly, AGL20 expression is positively regulated not only by the redundant vernalization and autonomous pathways of flowering but also by the photoperiod pathway. Our results indicate that AGL20 is an important integrator of three pathways controlling flowering in Arabidopsis.
... In recent years, it has become possible to promote flowering using biotechnologies. Nearly 30 years ago, Detlef Weigel and Ove Nilsson showed that flowering could be triggered in aspen by transgenic expression of a gene from Arabidopsis called LEAFY (LFY) [13]. From that pioneering work, scientists quickly move to cultivated species, including fruit species such as apple. ...
... Association mapping or linkage disequilibrium (LD) mapping [16] or, alternatively, linkage mapping using bi-parental populations [17,18] are usually preferred to screen markers located near the trait of interest, although some simplified methods, such as bulk segregant analysis, have been used successfully ( Figure 1) [19]. flowering could be triggered in aspen by transgenic expression of a gene from Arabidopsis called LEAFY (LFY) [13]. From that pioneering work, scientists quickly move to cultivated species, including fruit species such as apple. ...
... In the context of using molecular markers in VOCs research, a full-sib parental mapping population was used to conduct a QTL survey to evaluate the VOC segregation found in apple fruit collected after a two-month postharvest storage period using a novel proton transfer reaction time of flight mass spectrometry (PTR-ToF-MS) [203]. A group of QTLs distributed over ten chromosomes in the population, such as linkage groups LG2, 3,4,5,11,13,14,15, and 16, were identified through the combined analysis of markers and phenotypic data. The QTLs found in these areas had LOD values ranging from 3.52 to 14.2, and their respective expressed variance percentages ranged from 26% to 68.9%. ...
Breeding fruit species is time-consuming and expensive. With few exceptions, trees are likely the worst species to work with in terms of genetics and breeding. Most are characterized by large trees, long juvenile periods, and intensive agricultural practice, and environmental variability plays an important role in the heritability evaluations of every single important trait. Although vegetative propagation allows for the production of a significant number of clonal replicates for the evaluation of environmental effects and genotype × environment interactions, the spaces required for plant cultivation and the intensity of work necessary for phenotypic surveys slow down the work of researchers. Fruit breeders are very often interested in fruit traits: size, weight, sugar and acid content, ripening time, fruit storability, and post-harvest practices, among other traits relevant to each individual species. The translation of trait loci and whole-genome sequences into diagnostic genetic markers that are effective and affordable for use by breeders, who must choose genetically superior parents and subsequently choose genetically superior individuals among their progeny, is one of the most difficult tasks still facing tree fruit geneticists. The availability of updated sequencing techniques and powerful software tools offered the opportunity to mine tens of fruit genomes to find out sequence variants potentially useful as molecular markers. This review is devoted to analysing what has been the role of molecular markers in assisting breeders in selection processes, with an emphasis on the fruit traits of the most important fruit crops for which examples of trustworthy molecular markers have been developed, such as the MDo.chr9.4 marker for red skin colour in apples, the CCD4-based marker CPRFC1, and LG3_13.146 marker for flesh colour in peaches, papayas, and cherries, respectively.
... LFY orchestrates floral meristem emergence 1 and regulates floral meristem identity through the activation of floral homeotic genes. [2][3][4][5] Lossof-function mutants for the LFY gene are unable to form proper flowers and often show abnormal, leaf-like structures. 2,6 In contrast, ectopic LFY expression causes the conversion of lateral meristem as well as inflorescence meristem into flowers. ...
... 2,6 In contrast, ectopic LFY expression causes the conversion of lateral meristem as well as inflorescence meristem into flowers. 3 LFY encodes a plant-specific transcription factor with a C-terminal DNAbinding domain [7][8][9] and an N-terminal sterile alpha motif (SAM) domain, which is important for LFY oligomerization. 10,11 LFY specifies the time and place of flower development, and precise control of LFY expression is crucial. ...
... The ability of LFY to trigger flower formation onto inflorescences 3,6 and to reprogram root cells into flowers 34,35 prompted us to investigate deeper the nature and properties of LFY cytoplasmic foci in root cells from 35S::LFY-YFP plants. Several cellular structures exist as vesicles that yield punctate cytoplasmic signals similar in size and shape to LFY-YFP foci when observed by confocal microscopy, including Golgi, trans-Golgi network/early endosomes (TGN/EE), late endosomes (LE), and autophagosomes. ...
The transcription factor LEAFY (LFY) plays crucial roles in flower development by activating floral homeotic genes. Activation of LFY targets requires the combined action of LFY and the E3 ubiquitin ligase UFO, although the precise underlying mechanism remains unclear. Here, we show that LFY accumulates in biomolecular condensates within the cytoplasm, while recombinant LFY forms condensates with similar properties in vitro. UFO interacts with LFY within these condensates and marks it for degradation. LFY levels in the nucleus are buffered against changes in total LFY levels induced by proteasome inhibition, UFO overexpression, or mutation of lysine residues in a disordered region of LFY. Perturbation of cytoplasmic LFY condensates by 1,6-hexanediol treatment induces the relocalization of LFY to the nucleus and the subsequent activation of the LFY target AP3 in flowers. Our data suggest that nucleocytoplasmic partitioning, condensation, and ubiquitin-dependent degradation regulate LFY levels in the nucleus to control its activity.
... LFY gene orthologs are found in a wide variety of flowering and non-flowering plant species. In many developmental contexts, LFY is needful to specify a meristem as floral (Weigel and Nilsson, 1995). Beside this, LFY serves two key roles in specifying flowers. ...
... Lfyap1 plant has a phenotype just like that of 35S:TFL1 (Weigel et al., 1992). Ectopic expression of LFY or AP1 converts the inflorescence shoot apical meristem to a flower; 35S:AP1 and 35S: LFY flower show a terminal flower phenotype just like that of tfl1 mutants (Weigel and Nilsson, 1995). Although AP1 and LFY are the major floral meristem identity genes, other genes along with CAULIFLOWER (Kempin et al., 1995), FRUITFULL (Ferrandiz et al., 2000) and AP2 (Jofuku et al., 1994) play secondary roles in specifying floral meristem identity. ...
... AP1 is a member of the MADS family (Mandel et al., 1992), whereas LFY encodes a plant-specific protein that display no strong similarity to other genes in Arabidopsis (Weigel et al., 1992). In many developmental context's transcription of AP1 and LFY in lateral meristems is sufficient to specify them as floral (Weigel and Nilsson, 1995). Signals from the four primary floral inductive pathways are integrated by FLC, SOC1, FT and LFY. ...
Flowers are arranged into articulated whorls of sepals, petals, stamens and carpels, each of which has a special reproductive function in each of these floral organ groups. Sepals enclose and cover the bud of the flower, while petals may be wide and showy to attract pollinators. Stamens produce male gametes containing pollen grains, while the carpels contain the ovules that will bear the seeds when fertilized. While the scale, form, number and development of each of these types of organs may be quite different, there is the same general arrangement of four types of floral organs organized in clustered whorls across all species of flowering plants. The identities of these exclusive organs are specified by the action of floral organ identity genes in discrete regions of developing flower. The main principle of flower development is the ABC model. Recent work has led identification of SEP genes which work redundantly to determine petals, stamens, and carpels as well as floral determination. The update of the ABC model resulted in the discovery of the value of the SEP genes. The failure of floral organs to grow with the correct identity in A, B, C and E class mutants suggests that the ABCE genes are necessary to specify the identity of floral organ.
... One of these is LEAFY (LFY), which encodes a new type of transcription factor that is required for the switch from vegetative to reproductive development in Arabidopsis and other dicots (Coen et al., 1990;Schultz & Haughn, 1991;Huala & Sussex, 1992;Weigel et al., 1992;Hofer et al., 1997;Parcy et al., 1998;Souer et al., 1998). Importantly, overexpression of LFY is sufficient for the transformation of lateral shoots into flowers, and causes early flowering in several dicots, including Arabidopsis, aspen and tobacco (Weigel & Nilsson, 1995). ...
... Plasmid pDW151, which contains a LFY cDNA driven by the cauliflower mosaic virus 35S promoter, has been described (Weigel & Nilsson, 1995). Rice (Oryza sativa L. Japonica cv. ...
... It is notable that overexpression of Arabidopsis LFY affected flowering time in rice, while the converse experiment, overexpression of the rice LFY homolog RFL in Arabidopsis, had no clear effect on floral meristem identity, although it induced a variety of developmental abnormalities (Kyozuka et al., 1998). In Arabidopsis, early flowering induced by LFY is partially mediated by the MADS box gene APETALA1 (AP1), which is precociously induced in 35S::LFY plants and acts together with LFY in the specification of floral meristem identity (Weigel & Nilsson, 1995;Parcy et al., 1998). Once the rice AP1 ortholog has been identified, it will be interesting to determ- ine whether the rice AP1 gene is also precociously induced in 35S::LFY rice plants. ...
Onset of flowering, or heading date, is an important agronomic trait of cereal crops such as rice and early-heading varieties are required for certain regions in which rice is cultivated. Since the floral control gene LEAFY from Ara-bidopsis can dramatically accelerate flowering in dictoyledonous plants, the usefulness of LEAFY for manipulating heading date in rice has been tested. Constitutive expression of LEAFY from the cauliflower mosaic virus 35S promoter caused early flowering in transgenic rice, with a heading date that was 26-34 days earlier than that of wild-type plants. Early flowering was accompanied by a small yield penalty and some panicle abnormality. These observations suggest that floral regulatory genes from Arabidopsis are useful tools for heading date improvement in cereal crops.
... In trees, it is difficult to obtain transgenic plants, therefore the mobility of FT protein can be used to generate grafted plants to promote flowering [20]. LFY has been reported to play roles in controlling flowering time in Arabidopsis [62], tobacco [31], Citrus [30], aspen [62], and gloxinia [32], but early-flowering transgenic apple trees [63] and poplar trees [36] have not been obtained. However, in poplar, the use of LFY-RNAi successfully suppressed the expression of the LFY gene to produce sterile plants [64]. ...
... In trees, it is difficult to obtain transgenic plants, therefore the mobility of FT protein can be used to generate grafted plants to promote flowering [20]. LFY has been reported to play roles in controlling flowering time in Arabidopsis [62], tobacco [31], Citrus [30], aspen [62], and gloxinia [32], but early-flowering transgenic apple trees [63] and poplar trees [36] have not been obtained. However, in poplar, the use of LFY-RNAi successfully suppressed the expression of the LFY gene to produce sterile plants [64]. ...
... However, in poplar, the use of LFY-RNAi successfully suppressed the expression of the LFY gene to produce sterile plants [64]. LFY and its homologous genes are inflorescence architecture regulators in Arabidopsis, rice and Jatropha; bracts were shown to grow vigorously on both LFY mutants and its RNAi background plants [27,47,62,65]. In previous and the current study, JcLFY-silenced Jatropha also presented reduced fertility [47]. ...
Production of normal gametes is necessary for flowering plant reproduction, which involves the transition from vegetative to reproductive stage and floral organ development. Such transitions and floral development are modulated by various environmental and endogenous stimuli controlled by sophisticated regulatory networks. FLOWERING LOCUS T (FT) and LEAFY (LFY) are two key genes that integrate signals from multiple genetic pathways in Arabidopsis. However, the comprehensive functions of and relationship between these two genes in trees are poorly understood. In this study, we found that JcFT played a vital role in regulating the flowering transition in the perennial woody species Jatropha curcas. JcLFY also involved in regulating this transition and controlled floral organ development. The non–flowering phenotype of JcFT-RNAi was rescued successfully by overexpression of JcLFY, while the abnormal flowers produced by JcLFY silencing were not recovered by JcFT overexpression via hybridization. These results indicate that JcFT, in which a mutation lead to a nonflowering phenotype, is the central gene of the floral meristem transition and that JcLFY, in which a mutation leads to striking changes in flowering and often sterility, is the central floral and inflorescence development gene. Moreover, our hybridization results suggest that JcLFY acts downstream of JcFT in Jatropha.
... LFY has been reported to play roles in controlling flowering time in Arabidopsis [62], tobacco [31], Citrus [30], aspen [62], and gloxinia [32], but early-flowering transgenic apple trees [63] and poplar trees [36] have not been obtained. However, in poplar, the use of LFY-RNAi successfully suppressed the expression of the LFY gene to produce sterile plants [64]. ...
... LFY has been reported to play roles in controlling flowering time in Arabidopsis [62], tobacco [31], Citrus [30], aspen [62], and gloxinia [32], but early-flowering transgenic apple trees [63] and poplar trees [36] have not been obtained. However, in poplar, the use of LFY-RNAi successfully suppressed the expression of the LFY gene to produce sterile plants [64]. ...
... However, in poplar, the use of LFY-RNAi successfully suppressed the expression of the LFY gene to produce sterile plants [64]. LFY and its homologous genes are inflorescence architecture regulators in Arabidopsis, rice and Jatropha; bracts were shown to grow vigorously on both LFY mutants and its RNAi background plants [27,47,62,65]. In previous and the current study, JcLFY-silenced Jatropha also presented reduced fertility [47]. ...
Production of normal gametes is necessary for flowering plant reproduction, which involves the transition from vegetative to reproductive stage and floral organ development. Such transitions and floral development are modulated by various environmental and endogenous stimuli and controlled by sophisticated regulatory networks. FLOWERING LOCUS T (FT) and LEAFY (LFY) are two key genes that integrate signals from multiple genetic pathways in Arabidopsis. However, the comprehensive functions and relationship between these two genes in trees are poorly understood. In this study, we found that JcFT played a vital role in regulating the flowering transition in the perennial woody species Jatropha curcas. JcLFY also involved in regulating this transition and controlled floral organ development. The non–flowering phenotype of JcFT-RNAi was rescued successfully by overexpression of JcLFY, while the abnormal flowers produced by JcLFY silencing were not recovered by JcFT overexpression via hybridization. These results indicate that JcFT, in which a mutation leads to a nonflowering phenotype, is the central gene of the floral meristem transition and that JcLFY, in which a
mutation leads to striking changes in flowering and often sterility, is the central floral and inflorescence development gene. Moreover, our hybridization results suggest that JcLFY acts downstream of JcFT in Jatropha.
... Among the MADS-box TFs, APETALA1 (AP1) and SEPALLATA3 (SEP3) were proposed to act as pioneer TFs since they can access closed chromatin (Pajoro et al., 2014). The LFY gene encodes a plant-specific helix-turn-helix TF (Weigel et al., 1992;Weigel and Nilsson, 1995;Hamès et al., 2008). Although overexpression of LFY alone cannot induce ectopic flower formation and does not alter embryogenesis and root formation, overexpression of LFY with WUSCHEL (encoding a homeodomain TF that promotes stem cell formation) in root tissues conferred floral fate to root cells (Gallois et al., 2004;Wagner et al., 2004). ...
... In addition to the 2.3-kilobase-pair upstream intergenic LFY promoter region, which contains distal and proximal elements, the genic region of LFY also plays key roles in this integration (Figure 2A; Blázquez et al., 1997Blázquez et al., , 1998Blázquez and Weigel, 2000;Yamaguchi et al., 2009Yamaguchi et al., , 2013Yamaguchi et al., , 2016Wu et al., 2015;Zhu et al., 2020). The precocious expression of LFY in plants during the vegetative phase led to premature flower formation (Weigel and Nilsson, 1995). As a result, these plants produced few seeds. ...
... LFY has the ability to convert cell fate when overexpressed (Weigel and Nilsson, 1995;Wagner et al., 1999Wagner et al., , 2004fourth property). Loss or reduction of LFY activity resulted in an increased number of secondary inflorescences, whereas constitutive overexpression of LFY caused precocious flower formation without secondary inflorescences ( Figure 2F; Weigel et al., 1992;Weigel and Nilsson, 1995). ...
A subset of eukaryotic transcription factors (TFs) possess the ability to reprogram one cell type into another. Genes important for cellular reprograming are typically located in closed chromatin, which is covered by nucleosomes. Pioneer factors are a special class of TFs that can initially engage their target sites in closed chromatin prior to the engagement with, opening of, or modification of the sites by other factors. Although many pioneer factors are known in animals, a few have been characterized in plants. The TF LEAFY (LFY) acts as a pioneer factor specifying floral fate in Arabidopsis. In response to endogenous and environmental cues, plants produce appropriate floral inducers (florigens). During the vegetative phase, LFY is repressed by the TERMINAL FLOWER 1 (TFL1)–FD complex, which functions as a floral inhibitor, or anti-florigen. The florigen FLOWERING LOCUS T (FT) competes with TFL1 to prevent the binding of the FD TF to the LFY locus. The resulting FT–FD complex functions as a transient stimulus to activate its targets. Once LFY has been transcribed in the appropriate spatiotemporal manner, LFY binds to nucleosomes in closed chromatin regions. Subsequently, LFY opens the chromatin by displacing H1 linker histones and recruiting the SWI/SNF chromatin-remodeling complex. Such local changes permit the binding of other TFs, leading to the expression of the floral meristem identity gene APETALA1. This mini-review describes the latest advances in our understanding of the pioneer TF LFY, providing insight into the establishment of gene expression competence through the shaping of the plant epigenetic landscape.
... The FveLFY overexpression lines were selected and validated by RT-qPCR (Fig. 3, B and C). In the FveLFYa-ox lfy-5 and FveLFYb-ox lfy-5 transgenic lines, the primary shoots terminate with a few flowers, and secondary shoots are replaced by solitary flowers (Fig. 3D), resembling the AtLFY-ox plants (Weigel and Nilsson 1995). In the Col-0 background, the FveLFYa-ox lines also produce solitary flowers and fewer flowers, while the FveLFYb-ox lines only have more branches with fewer flowers, indicating early determinacy of the inflorescences (Fig. 3E). ...
... Overexpression of FveLFYa in fvelfya-1 largely rescued the mutant's phenotype, which confirmed that FveLFYa is the causative gene. In the Arabidopsis LFY-ox plants, flowering is accelerated, the primary shoot terminates with a flower, and solitary flowers develop from the axils of the rosette leaves (Weigel and Nilsson 1995). By contrast, the FveLFYa-ox plants showed a delay in flowering, which may result from their suppressed vegetative growth. ...
The plant-specific transcription factor LEAFY (LFY), generally maintained as a single copy gene in most angiosperm species, plays critical roles in flower development. The woodland strawberry (Fragaria vesca) possesses four LFY homologs in the genome; however, their respective functions and evolution remain unknown. Here, we identified and validated that mutations in one of the four LFY homologs, FveLFYa, cause homeotic conversion of floral organs and reiterative outgrowth of ectopic flowers. In contrast to FveLFYa, FveLFYb/c/d appear dispensable under normal growth conditions, as fvelfyc mutants are indistinguishable from wild type and FveLFYb and FveLFYd are barely expressed. Transgenic analysis and yeast one-hybrid assay showed that FveLFYa and FveLFYb, but not FveLFYc and FveLFYd, are functionally conserved with AtLFY in Arabidopsis (Arabidopsis thaliana). Unexpectedly, LFY binding site prediction and yeast one-hybrid assay revealed that the transcriptional links between LFY and the APETALA1 (AP1) promoter/the large AGAMOUS (AG) intron are missing in F. vesca, which is due to the loss of LFY binding sites. The data indicate that mutations in cis-regulatory elements could contribute to LFY evolution. Moreover, we showed that FveLFYa is involved in leaf development, as approximately 30% of mature leaves have smaller or fewer leaflets in fvelfya. Phylogenetic analysis indicated that LFY homologs in Fragaria species may arise from recent duplication events in their common ancestor and are undergoing convergent gene loss. Together, these results provide insight into the role of LFY in flower and leaf development in strawberry and have important implications for the evolution of LFY.
... Previous studies revealed that the LFY gene acts as a switch that induces floweri Overexpression of LFY induces early flowering in Arabidopsis transgenic plants [27] transgenic Chinese cabbage plant developed by RNA interference-media transformation displayed late bolting and flowering due to the downregulation of L gene expression [28]. Transgenic plants were found to continue to grow in the vegetat stage. ...
... Previous studies revealed that the LFY gene acts as a switch that induces flowering. Overexpression of LFY induces early flowering in Arabidopsis transgenic plants [27]. A transgenic Chinese cabbage plant developed by RNA interference-mediated transformation displayed late bolting and flowering due to the downregulation of LFY gene expression [28]. ...
Chinese cabbage has unintended bolting in early spring due to sudden climate change. In this study, late-bolting Chinese cabbage lines were developed via mutagenesis of the BrLEAFY (BrLFY) gene, a transcription factor that determines floral identity, using the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9) system. Double-strand break of the target region via gene editing based on nonhomologous end joining (NHEJ) was applied to acquire useful traits in plants. Based on the ‘CT001’ pseudomolecule, a single guide RNA (sgRNA) was designed and the gene-editing vector was constructed. Agrobacterium-mediated transformation was used to generate a Chinese cabbage line in which the sequence of the BrLFY paralogs was edited. In particular, single base inserted mutations occurred in the BrLFY paralogs of the LFY-7 and LFY-13 lines, and one copy of T-DNA was inserted into the intergenic region. The selected LFY-edited lines displayed continuous vegetative growth and late bolting compared to the control inbred line, ‘CT001’. Further, some LFY-edited lines showing late bolting were advanced to the next generation. The T-DNA-free E1LFY-edited lines bolted later than the inbred line, ‘CT001’. Overall, CRISPR/Cas9-mediated mutagenesis of the BrLFY gene was found to delay the bolting time. Accordingly, CRISPR/Cas9 is considered an available method for the molecular breeding of crops.
... The constitutive expression of LFY and AP1 flower meristem genes led to the reduction of the generation time of perennials including hybrid aspen and citrus relatives [99,112,113]. The constitutive overexpression of the Arabidopsis AP1 gene caused the early flowering of tomatoes and silver birch [114,115]. ...
... The transgenic apple overexpressing MdFT1 showed an early flowering phenotype [119]. Along with FT and AP flowering genes, overexpressed basic helix-loop-helix transcription factor gene, SlbHLH22 also induced early flowering and fruit ripening in tomatoes [112]. It has been reported that the overexpression of CO-like genes induced a graft transmissible phloem mobile FT signal to accelerate flowering [20,120]. ...
During shoot apex development, the plants undergo a very complex transition phase of flowering for successful reproduction, seed/cone setting and fruit development. The conversion of vegetative shoot meristems to floral meristems depends upon numerous endogenous, exogenous factors and flowering genes for the development of floral parts. The perennial crops suffer from the limitation of the innate ability to keep some meristems in the vegetative state for the polycarpic growth habit leading to the long juvenile phase. Conventional breeding approaches viz. selection of early flowering parental lines, flower thinning and grafting are time-consuming requiring more time for the release of a new cultivar which is undesirable for rapid crop improvement. The best way to accelerate the perennial plant breeding improvement programs and to reduce the long juvenile phase is the induction of early flowering through the utilization of biotechnological approaches. The ability to allow the transmission of an early flowering gene to the progeny in a Mendelian fashion is the major advantage of biotechnological interventions. The introgression of early flowering traits from non-commercial germplasm or sexually compatible species to perennial species through the biotechnological aspects will act as a boon for crop improvement in future studies. The present review gives an overview of various flowering genes in perennial crops accompanying the implementation of biotechnological approaches including overexpression studies, RNA interference, Virus-induced flowering and CRISPR-Cas approaches that will help in reducing the period for induction of flowering in perennial crops.
... Discrete variation, especially in sympatric taxa, is usually taken as an indication for the presence of distinct lineages, even if ITS may not provide sufficient resolution (Magain et al., 2017). However, another explanation for discrete variation is developmental switching, in which environmental triggers determine whether individuals of the same population and genotype develop one discrete morph or another (Lively, 1986;Moran, 1992;Weigel & Nilsson, 1995;West-Eberhard, 2003;Chevin & Lande, 2013;Futuyma, 2015;Chevin & Hoffmann, 2017;Sieriebriennikov et al., 2018). This phenomenon could explain mismatches between phenotype and lineage assignment in species complexes (Muggia et al., 2008(Muggia et al., , 2014Lumbsch & Leavitt, 2011;Leavitt et al., 2011;Boluda et al., 2019). ...
... This phenomenon has been extensively investigated in animals, which are characterized by a closed body plan (Lively, 1986;Moran, 1992;Chevin & Lande, 2013;Futuyma, 2015;Chevin & Hoffmann, 2017;Sieriebriennikov et al., 2018). In plants and fungi including lichens, which have an open body plan, discrete polymorphism is less well studied (Weigel & Nilsson, 1995), also because it often cannot be readily quantified. In lichens, the 'environmental trigger' may be the type of photobiont, e.g. ...
We assessed the status of two New Zealand endemic morphodemes in the genus Sticta, currently treated as two separate taxa, Sticta filix and Sticta lacera. Both are green-algal lichens with a distinct stipe that grow in forested habitats and are suitable indicators of the indigenous vegetation health in forest ecosystems in New Zealand. They exhibit different morphologies and substrate ecologies: S. filix forms rather robust thalli, often on exposed trunks of phorophytes, with erect stems distinctly emerging from the substrate, whereas S. lacera is a more delicate lichen growing near the base of trees, usually among bryophyte mats or sheltered in the exposed portions of the phorophyte root-plate, with a prostrate, branched, stolon-like stem barely emerging from the substrate. Throughout their range, both taxa grow sympatrically and often in close proximity (syntopically). Despite the differences, ITS barcoding does not support the two morphodemes as separate species. In this study we assessed two possible explanations: (1) S. filix and S. lacera are discrete phenotypes of a single species, caused by developmental switching triggered by a discrete environmental variable, the propagules developing either on bare substrate or between bryophytes; and (2) the two morphodemes represent separate lineages, but ITS does not provide sufficient resolution to reflect this. We performed a quantitative analysis of morphological and ecological parameters, based on vouchered herbarium collections and field observations on iNaturalist NZ (https://inaturalist.nz), to assess the level of discreteness of the growth forms and to test for a correlation with the presence of a bryophyte mat. We further took advantage of an existing molecular data set from a target capture approach, comprised of 205 protein markers. This data set was used to establish a framework of percentage identities between pairs of the same and of different species among lobarioid Peltigeraceae and then to test whether the S. filix/lacera pairing fell closer to a within-species or a between-species pairing. The morphometric analysis of herbarium material resolved S. filix and S. lacera as two discrete morphs with little overlap, supported by numerous observations on iNaturalist NZ. However, whereas herbarium material suggested a significant association of the lacera morph with bryophyte mats, no such pattern was evident from field images on iNaturalist NZ, in which both morphs frequently associated with bryophyte mats. This highlights the limitations of herbarium material to correctly assess substrate ecology, whereas iNaturalist NZ postings had issues with correct identifications, given that especially S. lacera is easily confused with Pseudocyphellaria multifida. Based on the target capture data, the percentage identity of the S. filix/lacera pairing (99.43%) was significantly higher than that of all 12 between-species pairings (93.20–98.01%); it was at the same time lower than that of all within-species pairings (99.63–99.99%) but significantly so only in comparison with five out of the eight within-species pairings. The target capture approach is thus inconclusive, but the combination of all data suggests that S. filix and S. lacera are not discrete morphodemes of a single species but represent two separate lineages which emerged recently and hence cannot be resolved using the ITS barcoding marker or even a deeper phylogenomic approach based on protein-coding markers. We propose transplantation experiments and the application of RADseq to further assess this situation.
... Discrete variation, especially in sympatric taxa, is usually taken as an indication for the presence of distinct lineages, even if ITS may not provide sufficient resolution (Magain et al., 2017). However, another explanation for discrete variation is developmental switching, in which environmental triggers determine whether individuals of the same population and genotype develop one discrete morph or another (Lively, 1986;Moran, 1992;Weigel & Nilsson, 1995;West-Eberhard, 2003;Chevin & Lande, 2013;Futuyma, 2015;Chevin & Hoffmann, 2017;Sieriebriennikov et al., 2018). This phenomenon could explain mismatches between phenotype and lineage assignment in species complexes (Muggia et al., 2008(Muggia et al., , 2014Lumbsch & Leavitt, 2011;Leavitt et al., 2011;Boluda et al., 2019). ...
... This phenomenon has been extensively investigated in animals, which are characterized by a closed body plan (Lively, 1986;Moran, 1992;Chevin & Lande, 2013;Futuyma, 2015;Chevin & Hoffmann, 2017;Sieriebriennikov et al., 2018). In plants and fungi including lichens, which have an open body plan, discrete polymorphism is less well studied (Weigel & Nilsson, 1995), also because it often cannot be readily quantified. In lichens, the 'environmental trigger' may be the type of photobiont, e.g. ...
We assessed the status of two New Zealand endemic morphodemes in the genus Sticta, currently treated as two separate taxa, Sticta filix and Sticta lacera. Both are green-algal lichens with a distinct stipe that grow in forested habitats and are suitable indicators of the indigenous vegetation health in forest ecosystems in New Zealand. They exhibit different morphologies and substrate ecologies: S. filix forms rather robust thalli, often on exposed trunks of phorophytes, with erect stems distinctly emerging from the substrate, whereas S. lacera is a more delicate lichen growing near the base of trees, usually among bryophyte mats or sheltered in the exposed portions of the phorophyte root-plate, with a prostrate, branched, stolon-like stem barely emerging from the substrate. Throughout their range, both taxa grow sympatrically and often in close proximity (syntopically). Despite the differences, ITS barcoding does not support the two morphodemes as separate species. In this study we assessed two possible explanations: (1) S. filix and S. lacera are discrete phenotypes of a single species, caused by developmental switching triggered by a discrete environmental variable, the propagules developing either on bare substrate or between bryophytes; and (2) the two morphodemes represent separate lineages, but ITS does not provide sufficient resolution to reflect this. We performed a quantitative analysis of morphological and ecological parameters, based on vouchered herbarium collections and field observations on iNaturalist NZ (https://inaturalist.nz), to assess the level of discreteness of the growth forms and to test for a correlation with the presence of a bryophyte mat. We further took advantage of an existing molecular data set from a target capture approach, comprised of 205 protein markers. This data set was used to establish a framework of percentage identities between pairs of the same and of different species among lobarioid Peltigeraceae and then to test whether the S. filix/lacera pairing fell closer to a within-species or a between-species pairing. The morphometric analysis of herbarium material resolved S. filix and S. lacera as two discrete morphs with little overlap, supported by numerous observations on iNaturalist NZ. However, whereas herbarium material suggested a significant association of the lacera morph with bryophyte mats, no such pattern was evident from field images on iNaturalist NZ, in which both morphs frequently associated with bryophyte mats. This highlights the limitations of herbarium material to correctly assess substrate ecology, whereas iNaturalist NZ postings had issues with correct identifications, given that especially S. lacera is easily confused with Pseudocyphellaria multifida. Based on the target capture data, the percentage identity of the S. filix/lacera pairing (99.43%) was significantly higher than that of all 12 between-species pairings (93.20-98.01%); it was at the same time lower than that of all within-species pairings (99.63-99.99%) but significantly so only in comparison with five out of the eight within-species pairings. The target capture approach is thus inconclusive, but the combination of all data suggests that S. filix and S. lacera are not discrete morphodemes of a single species but represent two separate lineages which emerged recently and hence cannot be resolved using the ITS barcoding marker or even a deeper phylogenomic approach based on protein-coding markers. We propose transplantation experiments and the application of RADseq to further assess this situation.
... Significantly high LcLFY gene expression was recorded in the early-flowering genotype L4775. Similar high-expression of the LFY gene causing early-flowering is also reported in Arabidopsis (Weigel and Nilsson, 1995), rice (He et al., 2000), and strawberry (Liu et al., 2017). In the LcLFY gene, 12 SNPs/InDel-based allelic variants were recorded, which may be the reason for lower expression of LcLFY gene and delayed flowering in the Globe Mutant. ...
Developing early maturing lentil has the potential to minimize yield losses, mainly during terminal drought. Whole‐genome resequencing (WGRS) based QTL‐seq identified the loci governing earliness in lentil. The genetic analysis for maturity duration provided a good fit to 3:1 segregation (F2), indicating earliness as a recessive trait. WGRS of Globe Mutant (late parent), late‐flowering, and early‐flowering bulks (from RILs) has generated 1124.57, 1052.24 million raw and clean reads, respectively. The QTL‐Seq identified three QTLs (LcqDTF3.1, LcqDTF3.2, and LcqDTF3.3) on chromosome 3 having 246244 SNPs and 15577 insertions/deletions (InDels) and 13 flowering pathway genes. Of these, 11 exhibited sequence variations between bulks and validation (qPCR) revealed a significant difference in the expression of nine candidate genes (LcGA20oxG, LcFRI, LcLFY, LcSPL13a, Lcu.2RBY.3g060720, Lcu.2RBY.3g062540, Lcu.2RBY.3g062760, LcELF3a, and LcEMF1). Interestingly, the LcELF3a gene showed significantly higher expression in late‐flowering genotype and exhibited substantial involvement in promoting lateness. Subsequently, an InDel marker (I‐SP‐383.9; LcELF3a gene) developed from LcqDTF3.2 QTL region showed 82.35% PVE (phenotypic variation explained) for earliness. The cloning, sequencing, and comparative analysis of the LcELF3a gene from both parents revealed 23 SNPs and InDels. Interestingly, a 52 bp deletion was recorded in the LcELF3a gene of L4775, predicted to cause premature termination of protein synthesis after 4 missense amino acids beyond the 351st amino acid due to the frameshift during translation. The identified InDel marker holds significant potential for breeding early maturing lentil varieties.
... One of the most intriguing possibilities for shortening the breeding cycle involves the biotechnologically altering the genetic flowering pathways. Almost two decades ago, Weigel and Nilsson (1995) found that by introducing a specific gene from Arabidopsis called LEAFY (LFY) through genetic modification, they were able to induce the flowering process. Over the past two decades, there has been significant progress in refining this ground breaking technology. ...
Given the rapid growth of the global population, it is crucial to accelerate food production to meet the ever-increasing demand for food and nutrition. Given the limited potential for expanding cultivation areas, it is crucial for plant breeders to prioritize the development of new varieties that not only have higher productivity but also possess the ability to withstand different types of pests, diseases and environmental challenges. Nevertheless, the development of new varieties requires a meticulous and time-consuming process. The duration of a breeding program is primarily determined by the number of years needed to develop homozygous lines from the segregating generations resulting from the crossbreeding of two parents. Woody perennial plants, such as fruit and nut trees, often have lengthy breeding cycles. Plant breeders may need to go through multiple cycles and wait for several years to develop and introduce improved cultivars. However, recent advancements in biotechnologies and genomics have the potential to greatly accelerate cultivar development in all crops. Through the utilization of various genetic engineering techniques, Fast-track breeding systems are able to induce early flowering, leading to generation cycles of one year or less. This method has been used on various crops to effectively generate homozygous lines after crossing carefully selected parents with contrasting traits. The technique is dependent on precise control of various factors including photoperiod, light intensity, temperature, soil moisture, soil nutrition, and high-density planting. This brief review provides an overview of strategies aimed at minimizing the frequency and length of breeding cycles for horticultural crops, while maximizing their yield.
... For example, in Arabidopsis, overexpression of LFY induces early flowering [15], whereas the Arabidopsis lfy mutant shows late flowering [7]. Similar situations can be found in many plants, including rice (Oryza sativa L.) [16], citrus (Citrus reticulata Blanco) [12], poplar (Populus tomentosa) [17], fig (Ficus carica L.) [13], and mango (Mangifera indica L.) [14]. Opposite results have also been reported; for example, overexpression of the tobacco LFY homologue NFL1 in Arabidopsis does not severely affect flowering [18]. ...
Background
Flowering at the right time is a very important factor affecting the stable annual yield of longan. However, a lack of knowledge of the regulatory mechanism and key genes of longan flowering restricts healthy development of the longan industry. Therefore, identifying relevant genes and analysing their regulatory mechanism are essential for scientific research and longan industry development.
Results
DlLFY (Dimocarpus longan LEAFY) contains a 1167 bp open reading frame and encodes 388 amino acids. The amino acid sequence has a typical LFY/FLO family domain. DlLFY was expressed in all tissues tested, except for the leaf, pericarp, and pulp, with the highest expression occurring in flower buds. Expression of DlLFY was significantly upregulated at the early flower induction stage in “SX” (“Shixia”). The results of subcellular localization and transactivation analysis showed that DlLFY is a typical transcription factor acting as a transcriptional activator. Moreover, overexpression of DlLFY in Arabidopsis promoted early flowering and restrained growth, resulting in reduced plant height and rosette leaf number and area in transgenic plants. DNA affinity purification sequencing (DAP-Seq) analysis showed that 13 flower-related genes corresponding to five homologous genes of Arabidopsis may have binding sites and be putative target genes. Among these five flower-related genes, only AtTFL1 (terminal flower 1) was strongly inhibited in transgenic lines.
Conclusion
Taken together, these results indicate that DlLFY plays a pivotal role in controlling longan flowering, possibly by interacting with TFL1.
... The interplay of these factors governing the same process provides an evidence that extensive cross-talk exists between different regulatory pathways (each pathway developmentally controlled by expression of specific genes), making the overall process a complex one (Jack, 2004), for example, the Leafy (LFY) and Apetala 1 (AP1) genes known to be involved in identity and initiation of floral meristem in an interactive manner as ap1 mutants overexpressing LFY fails to promote flowering while as lfy mutants overexpressing AP1 promotes flowering, but with abnormal floral organs (Weigel and Nilsson, 1995). As far as the influence of photoperiod on floral initiation is concerned, a specific photoreceptor (Phytochrome A) is known to play an important role in concurrence with some members of biological circadian clock (e.g., EARLY FLOW-ERING3). ...
This new volume presents some of the latest research trends and areas of improvement to benefit the floriculture industry and to understand its future directions and prospects. The research addresses the global floriculture industry’s shift from a traditional to a commercial focus. The global economy has spurred entrepreneurs to focus on the growing trend of exportoriented floriculture under controlled climatic conditions. The volume also looks at the role of plants in stabilizing the environment and the use of scientific knowledge through research that has changed the perspective of modern floriculture.
This new book is a valuable compilation of the latest research work and areas of improvement in floriculture today.
Key features:
Provides an overview of the global floriculture industry
Looks at the role of bulbous ornamentals
Considers enhancing consumer-preferred traits in floriculture crops through genetic manipulation
Discusses using ornamental plants to stabilize the environment
... Besides their polycarpic growth habits, perennial woody plants experience a long period of vegetative growth (including juvenile and adult vegetative growth) before reproductive onset. For example, it will take 5 to 20 y for seed-grown Populus trees until onset of flowering (26). Hybrid poplar (Populus tremula x alba, clone 717-1B4) trees originating from tissue culture explants will initiate flowering earlier, but not before 3 to 4 y after transplanting. ...
In temperate and boreal regions, perennial plants adapt their annual growth cycle to the change of seasons. In natural forests, juvenile seedlings usually display longer growth seasons compared to adult trees to ensure their establishment and survival under canopy shade. However, how trees adjust their annual growth according to their age is not known. In this study, we show that age-dependent seasonal growth cessation is genetically controlled and found that the miR156-SPL3/5 module, a key regulon of vegetative phase change (VPC), also triggers age-dependent growth cessation in Populus trees. We show that miR156 promotes shoot elongation during vegetative growth, and its targets SPL3/5s function in the same pathway but as repressors. We find that the miR156-SPL3/5s regulon controls growth cessation in both leaves and shoot apices and through multiple pathways, but with a different mechanism compared to how the miR156-SPL regulon controls VPC in annual plants. Taken together, our results reveal an age-dependent genetic network in mediating seasonal growth cessation, a key phenological process in the climate adaptation of perennial trees.
... The previous difference, likely affects the opposite functions of LFY in inflorescence development in these species. In Arabidopsis, constitutive expression of LFY (35S:LFY) results in conversion of both apical and axillary meristems into terminal flowers, demonstrating that LFY is a limiting factor defining when and where flowers are produced (Weigel and Nilsson, 1995). By contrast, constitutive expression of LFY in wheat increases the number of lateral spikelets, likely by delaying the IM>TS transition (Fig. 3). ...
In wheat, the transition of the inflorescence meristem (IM) to a terminal spikelet determines the spikelet number per spike (SNS) and the maximum number of grains. In this study, we demonstrate that the plant-specific transcription factor LEAFY (LFY) physically interacts with WHEAT ORTHOLOG OF APO1 (WAPO1), a protein encoded by a gene underlying a major QTL for SNS in wheat. Loss-of-function mutations in LFY, WAPO1 , or both result in significant and similar reductions in SNS, which indicates that both genes are required to maintain IM indeterminacy and prevent a precocious transition to a terminal spikelet. We also identify a significant genetic interaction between LFY and VERNALIZATION1 ( VRN1 ) and show that these genes play opposite roles in the regulation of SNS. To understand these interactions, we characterized the spatio-temporal distribution of these and other flowering genes during wheat spike development using single-molecule fluorescence in-situ hybridization. Finally, we identify natural LFY-B alleles that affect SNS, determine their interactions with natural alleles of WAPO-A1 , and select an allele combination that maximizes SNS for wheat improvement.
Summary Statement
In this study, we demonstrate that physical and genetic interactions between LFY and WAPO1 are critical to regulate spikelet number per spike, and we identify an optimum allele combination for wheat improvement.
... This behaviour in Arabidopsis thaliana may be partially explained by variations in the expression of the meristem identity gene LEAFY (LFY), which gradually increases throughout vegetative growth in noninducing conditions [133]. As photoperiod was shown to modulate the effect of constitutive LFY overexpression on flowering time [134], it has also been hypothesised that the apex changes in its competence to respond to LFY activity. In fact, analysis of LFY over-expression in late-flowering mutants demonstrated that some flowering time genes affected LFY transcription while others affected the response to LFY [135], and researchers are just now beginning to understand the underlying molecular mechanisms [136,137]. ...
Plants are extremely sensitive to changes in their environment, particularly variations in photoperiod or day length. Photoperiodism refers to a plant's capacity to detect variations in day length and make use of this knowledge to control key developmental processes including flowering, growth, and dormancy. Through a process known as photoperiodism, plants can detect and react to variations in the number of daylight hours, or photoperiod. The physiological response of plants to the length of day or night is known as photoperiodism. The plant uses this physiological response to time-critical developmental events like flowering. In this essay, I will cover the current understanding of how plants respond to photoperiod and the molecular mechanisms underpinning this response. Three groups of plants' photoperiodic responses can be distinguished: short-day plants (SDPs), long-day plants (LDPs), and day-neutral plants (DNPs). Whereas LDPs bloom when the length of the day exceeds the crucial threshold, SDPs do so only when it is shorter than the critical threshold. Conversely, DNPs do not have a crucial day duration and can bloom at any day length. Many genes and biochemical processes control how a plant responds to the photoperiod. The creation and movement of the hormone florigen, which starts blooming in response to photoperiodic signals, is a crucial regulating mechanism. On the other hand, a class of photoreceptors known as phytochromes is involved in the biochemical mechanisms driving photoperiodic responses in plants. The perception of light's duration, quality, and amount is caused by phytochromes. The red-light-absorbing Pr form and the far-red-light-absorbing Pfr form are the two interconvertible states in which they can exist. The ratio of Pr to Pfr is altered by the duration of light exposure and is utilizes by plants to assess day length. Exposure to light in SDPs causes the expression of the CONSTANS (CO) gene, and the CO protein causes the expression of the FLOWERING LOCUS T (FT), a gene that encourages flowering. By exposing LDPs to light, a different gene called GI (GIGANTEA) is induced rather than CO, which is normally expressed. The FT gene's expression is encouraged by GI's interaction with the protein ZEITLUPE (ZTL), which also encourages flowering. In addition to these essential elements, several proteins and signalling pathways are also involved in photoperiodic responses in plants. For instance, to optimise the response to variations in day length, the photoperiodic pathway interacts with the circadian clock, which controls numerous physiological processes in plants. In some species, the hormone gibberellin (GA) also aids in the promotion of flowering. One essential adaptation that enables plants to synchronize their developmental processes with seasonal changes is their capacity to react to variations in day length. Phytochromes play a key role in how plants perceive the day in the complex network of proteins and signalling channels that make up the molecular mechanisms behind photoperiodic responses in plants. There is still much to learn about the diversity and complexity of the photoperiodic response across several plant groupings, even if much is known about it in particular species.
... In accordance with a number of academic publications, scientists are currently using traditional genetic and molecular tools for the discovery, identification, and cloning of floral-specific genes, specifically the cloning of floral homeotic genes (Sung et al., 2000;Weigel and Nilsson, 1995). With the rapid advancement of proteome technology, the study of plant floral induction mechanisms has been greatly accelerated (Kofler et al., 2022;Munoz-Fambuena et al., 2013). ...
Proteome-based vegetative and flower bud formation characterization was utilized to identify and differentiate protein species with significant variable abundance during floral transition in mango cv. Dashehari using 2DE and corroborated the identified protein spots using gene expression analysis. Total soluble proteins were phenol-extracted from mango cv's vegetative and floral flush. Dashehari and separated on 2D gels at pH 4-7. The protein spots with variable intensity were identified through SameSpots software. The protein sequences of differentially accumulated spots were identified based on PI and MW using Citrus sinensis proteome isoelectric focusing database. Furthermore, these protein sequences were used to conduct (tBLASTn) against Mangifera indica to predict the protein. Real time gene expression was done to corroborate identified proteins. Total 301 spots were detected, out of which 16 were identified as differentially expressed (P?0.05) and a 2-fold change. These 16 protein spots were identified on the basis of in silico comparative mapping protein against genome of mango and citrus, a close relative. They were classified into eight categories: transcriptional regulation, phenylpropanoid pathway and cell wall /cytoskeleton metabolism-related proteins, hormone signalling, flowering time, signal-transduction, transport and protein synthesis to flowering. Five genes coding for shortlisted proteins were used for validation of results using gene expression analysis. SAM (S adenosyl methonine synthase) was found up-regulated in floral flush, involved in the biosynthesis of polyamines has association with flowering, and stress responses. Furthermore, ARF (Auxin Response Factor), serine/threonine kinase gene members were also found to play critical role in determining floral development process in mango, consistent with results obtained through 2DE. Protein species that are putatively involved in phenylpropanoid pathway were also identified, showing the process of mango flowering from a new perspective beyond the conventional view. This flowering related proteomics study provides an overview of the biological pathways and regulatory mechanisms associated with flowering developmental physiology.
... In the shoot apical meristem, FT interacts with FLOWERING LOCUS D (FD), a 14À3À3 structural protein and a bZIP transcription factor, to form an activation complex that will then induce expression of flower meristem identity genes (Abe et al., 2005;Corbesier et al., 2007;Jaeger and Wigge, 2007). The FT/FD complex triggers the expression of SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FRUITFUL (FUL), which will increase the expression of identity genes such as APETALA 1 (AP1) and LEAFY (LFY), which will form the flower meristem in the subsequent step (Schultz and Haughn, 1991;Weigel and Nilsson, 1995;Liljegren et al., 1999). ...
In this study, the FLOWERING LOCUS T (FT) gene, which has critical roles in flowering time, plant architecture, fruit, and seed development, was cloned and structurally characterized for the first time in apricot. Bioinformatic characterization analyses demonstrated that PaFT is evolutionarily conserved across different species. Expression analysis by RT-qPCR showed that PaFT may have a role in 12 different developmental stages of apricot.
... lfy-12 plants expressing LFY K249R or LFY K249S under the control of the LFY promoter developed flowers with normal sepals and carpels but with defective third-whorl and, more importantly, second-whorl organs, resulting in flowers similar to those observed in weak ufo mutants (Fig. 4d). When expressed under the constitutive 35S promoter, LFY K249R triggered ectopic flower formation and early flowering like WT LFY (Extended Data Fig. 8j), consistent with these LFY functions being independent of UFO and thus not affected by the K249R substitution 28 . ...
In angiosperms, flower development requires the combined action of the transcription factor LEAFY (LFY) and the ubiquitin ligase adaptor F-box protein, UNUSUAL FLORAL ORGANS (UFO), but the molecular mechanism underlying this synergy has remained unknown. Here we show in transient assays and stable transgenic plants that the connection to ubiquitination pathways suggested by the UFO F-box domain is mostly dispensable. On the basis of biochemical and genome-wide studies, we establish that UFO instead acts by forming an active transcriptional complex with LFY at newly discovered regulatory elements. Structural characterization of the LFY–UFO–DNA complex by cryo-electron microscopy further demonstrates that UFO performs this function by directly interacting with both LFY and DNA. Finally, we propose that this complex might have a deep evolutionary origin, largely predating flowering plants. This work reveals a unique mechanism of an F-box protein directly modulating the DNA binding specificity of a master transcription factor.
... The gene GAMYB is located at a distance of 44.2 kbp from the detected marker, while the gene NIGHTLIGHT-INDUCIBLE AND CLOCK-REGULATED 3 (LNK3) at a distance of 62.3 kbp. GAMYB is described as a regulator of flower induction, via the transcriptional activation of the LEAFY (LFY) gene (Gocal et al., 1999;Zhang et al., 2020), that results in early flowering both in dicots and monocot (Weigel and Nilsson, 1995;He et al., 2000). Instead, members of the family of NIGHTLIGHT-INDUCIBLE AND CLOCK-REGULATED (LNK1 and LNK2) genes are known to control photomorphogenic and photoperiodic responses, as well as circadian rhythms (Rugnone et al., 2013). ...
Establishing Lupinus mutabilis as a protein and oil crop requires improved varieties adapted to EU climates. The genetic regulation of strategic breeding traits, including plant architecture, growing cycle length and yield, is unknown. This study aimed to identify associations between 16 669 single nucleotide polymorphisms (SNPs) and 9 agronomic traits on a panel of 223 L. mutabilis accessions, grown in four environments, by applying a genome wide association study (GWAS). Seven environment-specific QTLs linked to vegetative yield, plant height, pods number and flowering time, were identified as major effect QTLs, being able to capture 6 to 20% of the phenotypic variation observed in these traits. Furthermore, two QTLs across environments were identified for flowering time on chromosome 8. The genes FAF, GAMYB and LNK, regulating major pathways involved in flowering and growth habit, as well as GA30X1, BIM1, Dr1, HDA15, HAT3, interacting with these pathways in response to hormonal and environmental cues, were prosed as candidate genes. These results are pivotal to accelerate the development of L. mutabilis varieties adapted to European cropping conditions by using marker-assisted selection (MAS), as well as to provide a framework for further functional studies on plant development and phenology in this species.
... Silencing of CAL alone does not cause any obvious phenotypic change, while silencing of CAL in the ap1 mutant background enhanced the phenotype of the plant, suggesting that CAL and AP1 may have redundant functions (Bowman et al., 1993). Using genetically modified Arabidopsis overexpressing LFY or AP1, it was shown that these genes are sufficient to promote flower initiation and development (Mandel and Yanofsky, 1995;Weigel and Nilsson, 1995). After constitutive transgenic expression of AP1 from Arabidopsis, early flowering was obtained in transgenic citrus (Peña et al., 2001) and tomato (Solanum lycopersicum) (Ellul et al., 2004). ...
Sorbitol is an important signaling molecule in fruit trees. Here, we observed that sorbitol increased during flower bud differentiation (FBD) in loquat (Eriobotrya japonica Lindl.). Transcriptomic analysis suggested that bud formation was associated with the expression of the MADS‐box transcription factor (TF) family gene, EjCAL. RNA fluorescence in situ hybridization showed that EjCAL was enriched in flower primordia but hardly detected in the shoot apical meristem. Heterologous expression of EjCAL in Nicotiana benthamiana plants resulted in early FBD. Yeast‐one‐hybrid analysis identified the ERF12 TF as a binding partner of the EjCAL promoter. Chromatin immunoprecipitation‐PCR confirmed that EjERF12 binds to the EjCAL promoter, and β‐glucuronidase activity assays indicated that EjERF12 regulates EjCAL expression. Spraying loquat trees with sorbitol promoted flower bud formation and was associated with increased expression of EjERF12 and EjCAL. Furthermore, we identified EjUF3GaT1 as a target gene of EjCAL and its expression was activated by EjCAL. Function characterization via overexpression and RNAi reveals that EjUF3GaT1 is a biosynthetic gene of flavonoid hyperoside. The concentration of the flavonoid hyperoside mirrored that of sorbitol during FBD and exogenous hyperoside treatment also promoted loquat bud formation. We identified a mechanism whereby EjCAL might regulate hyperoside biosynthesis and confirmed the involvement of EjCAL in flower bud formation in planta. Together, these results provide insight into bud formation in loquat and may be used in efforts to increase yield.
... Meanwhile, SOC1 interacts with the MADS transcription factor AGAMOUS-like 24 (AGL24) to upregulate the expression of LEAFY (LFY) (17). LFY and AP1 then promote the formation of floral meristems, the first step in the process of flower development (18,19). ...
Dodder ( Cuscuta spp.) is a genus of parasitic plants that form physiological bridges (haustoria) with their hosts to facilitate the transfer of water and nutrients. The parasites also repurpose nucleic acids and proteins translocating through the haustoria, potentially including the host florigen protein (FT), which is postulated to trigger floral transition in the parasite. Here, we identified the endogenous FT-FD flowering module in Cuscuta campestris . We detected the expression of two parasite-encoded C. campestris (Cc)FT genes in haustoria, whereas a newly found CcFD-like gene was expressed ubiquitously. C. campestris flowered while growing on mutant tobacco plants lacking the floral activators NtFT4 and NtFT5, indicating that host FT proteins are not required to initiate the parasite’s floral transition. We also showed that CcFT1 (identical to CaFT from Cuscuta australis ) and CcFT2 can rescue a non-flowering Ntft4 ⁻ Ntft5 ⁻ double knockout tobacco phenotype. Together, our results show that Cuscuta spp. produce a potent endogenous florigen as well as other proteins likely to be involved in floral transition. FT gene expression profiles in the haustoria suggest that Cuscuta spp. transition to flowering at least partly in response to host signals (e.g., sugars) that can activate the parasite’s FT-FD module. Although C. campestris and C. australis appear not to depend on the host FT protein for floral transition, the nature of the mobile host signals that influence floral development in these parasites remain unclear.
Significance Statement
Parasitic higher plants are known for their sophisticated adaptations that facilitate the transfer of water and nutrients from their hosts. They can also synchronize their transition from vegetative to reproductive development to match the host plant. Despite this high degree of synchronization, dodder plants maintain a potent endogenous floral activator module, which enables the parasite to switch to reproductive development autonomously. Synchronization must therefore involve other stimuli from the host plant, which are currently unknown. Understanding the environmental cues that trigger flowering, and the corresponding network of genetic and physiological regulators and integrators, may lead to new strategies that reduce the reproductive fitness of parasitic plants to protect crops and ensure food security.
Data Servers
This article is available as preprint (ID: BIORXIV/2022/520981) at https://www.biorxiv.org under the CC BY-NC 4.0 license. Reusable data files have been deposited at https://datadryad.org , accessible during peer-review under: https://datadryad.org/stash/share/DK8Olh2VqFwbGNL0GtkGt24dD0GhWhJn82oLBC1XK70
... Studies have shown the occurrence of splicing variants of CAL, for example, for BobCAL of cauliflower, a total of four alternative splicing variants are generated (Cao et al., 2020). As a MADS-box gene, CAL encodes proteins involved in flower meristem formation (Münster et al., 1997) and plays an important role in the identity specification of flower organs and in the transition from inflorescence to flower meristem (Bowman, 1993;Weigel and Nilsson, 1995). ...
CAULIFLOWER (CAL) genes and APETALA1 (AP1) genes are two closely related genes with redundant functions, both of which have unique functions in the process of flower meristem formation in Arabidopsis thaliana. MiCAL homologous genes play a key role in flower transformation and flower morphogenesis in Arabidopsis. Two CAL genes, MiCAL1 and MiCAL2, were cloned from mango (Mangifera indica L.). Its full-length sequence was 717 bp and 714 bp, encoding 239 and 238 amino acids, respectively. Both the MiCAL1 and MiCAL2 proteins contained typical MADS-box and K-box domains and therefore belonged to the CAL-like protein family. MiCAL1 and MiCAL2 were expressed in all tissues at the inflorescence elongation stage and flowering stage, with the highest expression in the leaves at the flowering stage. They have similar expression patterns during flower development, with the highest expression levels in leaves during flower differentiation and the lowest expression levels during fruit development. Overexpression of MiCAL1 and MiCAL2 resulted in the flowering of Arabidopsis significantly earlier. Overexpression of MiCAL1 resulted in terminal flowers with normal flower organs, while overexpression of MiCAL2 induced partial variation in floral organs but had no effect on inflorescences. Yeast two-hybrid (Y2H) experiments showed that MiCAL1 and MiCAL2 can interact with several flower-related proteins as well as stress response proteins, such as SEP1, SVP1, SVP2, SOC1G and Di19-4. These results suggest that these two MiCAL genes may have an important influence on mango flowering.
... Meanwhile, Arabidopsis lfy mutant shows late owering [7]. Similar phenomena can be found in many plants, including rice (Oryza sativa L.) [16], citrus (Citrus reticulata Blanco) [12], poplar (Populus tomentosa) [17], g (Ficus carica L.) [13], and mango (Mangifera indica L.) [14]. On the contrary, there are also opposite results; for example, overexpression of tobacco LFY homologue NFL1 in Arabidopsis does not severely affect owering [18]. ...
Backgroud: Flowering at the right time is a very important factor affecting the stable annual yield of longan. However, a lack of knowledge of the regulatory mechanism and key genes of longan flowering restricts the healthy development of the longan industry. Therefore, identifying the relevant genes and analyzing their regulatory mechanism are essential for scientific research and the development of the longan industry. Here, we isolated a LEAFY homologue gene from longan, DlLFY, and identified its function.
Results: DlLFY contains a 1167 bp open reading frame and encodes 388 amino acids. The amino acid sequence has a typical LFY/FLO family domain. DlLFY was expressed in all the tested tissues, expect for leaf, pericarp, and ulp, with the highest expression occurring in flower buds. The expression of DlLFY was significant upregulated at the early flower induction stage in “SX” (“Shixia”). The results of subcellular localization and transactivation analysis show that DlLFY is a kind of typical transcript factor with transcriptional activator. Moreover, overexpression of DlLFY in Arabidopsis promoted early flowering and restrained growth, resulting in reduced plant height and number and area of rosette leaves of transgenic plants. DNA affinity purification sequencing (DAP-Seq) analysis showed that 13 flower-related genes corresponding to five homologous genes of Arabidopsis may be the binding sites and putative target genes. Among these five flower-related genes, only AtTFL1 was strongly inhibited in transgenic lines.
Conclusion: Taken together, these results indicate that DlLFY plays a pivotal role in controlling longan flowering, possibly by negatively regulating TFL1.
... For example, AP1 and LFY CE simulations, predict that the SAM converts into the FM or a chimeric IFM meristem. Actually, 35S::AP1 plants are early flowering, and the SAM becomes a floral meristem that produces a terminal flower (Mandel and Yanofsky, 1995), besides, 35S::LFY plants are also early flowering and they develop solitary flowers instead of secondary shoots (Weigel and Nilsson, 1995). On the contrary, the FM disappeared in TFL1 and XAL2 CE simulation, and a chimeric IFM meristem is predicted, as has been reported in the literature for these mutant lines (Ratcliffe et al., 1998;Pérez-Ruiz et al., 2015). ...
Post-embryonic plant development is characterized by a period of vegetative growth during which a combination of intrinsic and extrinsic signals triggers the transition to the reproductive phase. To understand how different flowering inducing and repressing signals are associated with phase transitions of the Shoot Apical Meristem (SAM), we incorporated available data into a dynamic gene regulatory network model for Arabidopsis thaliana. This Flowering Transition Gene Regulatory Network (FT-GRN) formally constitutes a dynamic system-level mechanism based on more than three decades of experimental data on flowering. We provide novel experimental data on the regulatory interactions of one of its twenty-three components: a MADS-box transcription factor XAANTAL2 (XAL2). These data complement the information regarding flowering transition under short days and provides an example of the type of questions that can be addressed by the FT-GRN. The resulting FT-GRN is highly connected and integrates developmental, hormonal, and environmental signals that affect developmental transitions at the SAM. The FT-GRN is a dynamic multi-stable Boolean system, with 2²³ possible initial states, yet it converges into only 32 attractors. The latter are coherent with the expression profiles of the FT-GRN components that have been experimentally described for the developmental stages of the SAM. Furthermore, the attractors are also highly robust to initial states and to simulated perturbations of the interaction functions. The model recovered the meristem phenotypes of previously described single mutants. We also analyzed the attractors landscape that emerges from the postulated FT-GRN, uncovering which set of signals or components are critical for reproductive competence and the time-order transitions observed in the SAM. Finally, in the context of such GRN, the role of XAL2 under short-day conditions could be understood. Therefore, this model constitutes a robust biological module and the first multi-stable, dynamical systems biology mechanism that integrates the genetic flowering pathways to explain SAM phase transitions.
... In Physcomitrella patens, LFY regulates cell division in gametophytes and sporophyte (Tanahashi et al., 2005), whereas LFY homologs in the fern Ceratopteris richardii function in shoot development (Plackett et al., 2018). LFY is a floral meristem identity gene that controls multiple aspects of inflorescence development in the flowering plant Arabidopsis thaliana (Weigel and Nilsson, 1995), and it is active during reproductive structure development in gymnosperms (Dornelas and Rodriguez, 2005;Moyroud et al., 2017). An increase in the expression of LFY results in early flowering, and a mutation in LFY causes a transition of flowers into leaves and shoots (Weigel et al., 1992). ...
In flowering plants, the LEAFY (LFY) gene controls floral meristem activity. In early land plants such as mosses and ferns, it, however, has a minimum role in cell division and development of diploid sporophyte. Homology modeling, an accurate and efficient protein structure prediction method, was used to construct a 3D model of the LEAFY protein in nonflowering and flowering plants. The present study examines the following species: Charophyte green algae, Physcomitrella, Ceratopteris, Picea, and Arabidopsis, as they are the popularly used model organisms for developmental studies. LEAFY protein sequences from the model organisms were aligned by multiple sequence alignment. 3D models of the LEAFY protein from all the model organisms was constructed using the PHYRE2 program with 100% confidence, and the constructed models were evaluated using the MolProbity tool. On the basis of the conserved regions, Charophyte green algae shared 38–46% sequence similarity with Physcomitrella sp., 37–46% similarity with Ceratopteris sp., 33–41% similarity with Picea sp., and 32–38% similarity with Arabidopsis sp. The Motif Finder server identified the protein family domain FLO_LFY and LFY_SAM, whose function is floral meristem development. Secondary structure prediction analysis indicated that the LEAFY protein belongs to the alpha (α) protein class, which is stable against mutation and thus limits structural changes in the LEAFY protein. The study findings reveal two distinct clusters of the LFY gene from the common ancestor green algae. One cluster is present in nonflowering plants that include mosses, pteridophytes, and gymnosperms, and the other cluster is present in flowering plants that include orchids, monocots, dicots, and angiosperms.
... In the leaf, FT mRNA expression is positively regulated by CO Wigge et al., 2005), and FT protein translocates through the phloem by interacting with FT-INTERACTING PROTEIN 1 and SODIUM POTASSIUM ROOT DEFECTIVE 1 (Corbesier et al., 2007;Jaeger and Wigge, 2007;Liu et al., 2012;Zhu et al., 2016). In the shoot apex, FT protein interacts with FD and the resulting FT-FD complex directly promotes the expression of SUPPRESSOR OF OVEREXPRESSION OF CON-STANS 1 (SOC1) and FRUITFULL, and ultimately the floral meristem identity genes APETALA 1 (AP1) and LEAFY (LFY) (Schultz and Haughn, 1991;Weigel and Nilsson, 1995) to trigger flowering. During the activation of these genes, FT is likely to compete with TFL1 to bind to FD (Hanano and Goto, 2011), partly explaining the opposite effects of FT and TFL1 on flowering time. ...
During the transition to the reproductive phase, the shoot apical meristem switches from the developmental program that generates vegetative organs to instead produce flowers. In this study, we examined the genetic interactions of FLOWERING LOCUS T (FT)/TWIN SISTER OF FT (TSF) and TERMINAL FLOWER 1 (TFL1) in the determination of inflorescence meristem identity in Arabidopsis thaliana. The ft-10 tsf-1 mutants produced a compact inflorescence surrounded by serrated leaves (hyper-vegetative shoot) at the early bolting stage, as did plants overexpressing TFL1. Plants overexpressing FT or TSF (or both FT and TFL1) generated a terminal flower, as did tfl1-20 mutants. The terminal flower formed in tfl1-20 mutants converted to a hyper-vegetative shoot in ft-10 tsf-1 mutants. Grafting ft-10 tsf-1 or ft-10 tsf-1 tfl1-20 mutant scions to 35S:: FT rootstock plants produced a normal inflorescence and a terminal flower in the scion plants, respectively, although both scions showed similar early flowering. Misexpression of FT in the vasculature and in the shoot apex in wild-type plants generated a normal inflorescence and a terminal flower, respectively. By contrast, in ft-10 tsf-1 mutants the vasculature-specific misexpression of FT converted the hyper-vegetative shoot to a normal inflorescence, and in the ft-10 tsf-1 tfl1-20 mutants converted the shoot to a terminal flower. TFL1 levels did not affect the inflorescence morphology caused by FT/TSF overexpression at the early bolting stage. Taking these results together, we proposed that FT/TSF and TFL1 play antagonistic roles in the determination of inflorescence meristem identity, and that FT/TSF are more important than TFL1 in this process.
... In a lfy mutant of Arabidopsis thaliana, the first flower was converted into leafy shoots and some abnormal flowers were subsequently produced (Weigel et al. 1992). On the other hand, ectopic expression of LFY-homologous genes has been reported to induce several phenotypic alterations such as dwarfness and early flowering in A. thaliana and Nicotiana tabacum (Ahearn et al. 2001;Weigel and Nilsson 1995). ...
LEAFY (LFY), which encodes a plant-specific transcription factor, plays an important role in the transition from vegetative to reproductive development. Ectopic expression of LFY has been reported to induce dwarfism and early flowering in some model plants. In order to examine the possibility of using LFY for molecular breeding of ornamental plants, we produced and characterized transgenic plants ectopically expressing LFY from Arabidopsis thaliana (AtLFY) in the liliaceous ornamental plant Tricyrtis sp. Nine independent transgenic plants have been obtained, and all of them exhibited dwarf phenotypes compared with the vector control. These transgenic plants could be classified into three types according to the degree of dwarfism: one showed an extreamly dwarf phenotype with smaller leaves (Type I); two showed moderately dwarf phenotypes (Type II); and six showed slightly dwarf phenotypes (Type III). All of Type I, Type II and Type III transgenic plants produced flower buds 1-3 weeks earlier than the vector control. Vector control and Type III transgenic plants produced 1-4 apical flower buds, whereas Type I and Type II transgenic plants produced only a single apical flower bud. Type I and Type II transgenic plants often produced non-fully-opened flowers. Quantitative real-time reverse transcription-polymerase chain reaction analysis showed that the AtLFY expression level generally correlated with the degree of dwarfism. These results indicate that morphological alterations observed in the transgenic plants was induced by ectopic expression of AtLFY. Lower levels of ectopic expression of LFY may be valuable for producing dwarf and early flowering ornamental plants.
... FLO/LFY single mutants of dicotyledonous species show increased branching due to flower-to-bud transformation, suggesting that FLO/LFY proteins inhibit branching by promoting flower development [61,62]. In addition, LFY activity is partially dependent on environmental and internal factors, such as light conditions and plant age, and can be induced by exogenous GA treatment [63,64]. Previous studies have shown that SPL13 positively regulates the expression of SFT, a gene related to tomato inflorescences, by directly binding to the SFT promoter region and thus controls inflorescence development [65]. ...
Inflorescences are the main factor affecting fruit yield. The quantity and quality of inflorescences are closely related to fruit quality and yield. The presence of compound inflorescences in cherry tomatoes is well established, and it has been discovered by chance that compound racemes also exist in tomatoes. To explore the formation of compound inflorescences in tomato, transcriptome sequencing was performed on Moneymaker (MM) and Compound Inflorescence (CI) plants. In-florescences were collected in three periods (early, middle and late) in three replicates, for a total of 18 samples. Data analysis showed that the DEGs were most enriched in metabolic pathways and plant hormone signal transduction pathways. The DEGs were also enriched in the cell cycle pathway, photosynthesis pathway, carbon metabolism pathway and circadian rhythm pathway. We found that the FALSIFLORA (FA), COMPOUND INFLORESCENCE (S) and ANANTHA (AN) genes were involved in compound inflorescence development, not only revealing novel genes but also providing a rich theoretical basis for compound inflorescence development.
... Fifteen different poplar genes were selected as targets or tools for genetic containment ( Table 1). At the time of vector construction, with the exception of LEAFY and its poplar ortholog (Weigel and Nilsson, 1995;Rottmann et al., 2000), none of the genes had been characterized in transgenic poplar and sequence data was limited to cDNAs and the initial release of the P. trichocarpa genome sequence. Hence, the genes were selected primarily based on knowledge of, and homology to, genes characterized in A. thaliana. ...
... This indicates that the former species has the ability to outcompete the latter by quickly utilizing the available nutrient resources in the soil. These findings substantiate the generalized statements by Weigel & Nilsson (1995) supported by Amasino (2004) that vegetative growth and sexual reproduction are controlled by several intrinsic as well as extrinsic factors. Sen (1977) wrote that T. purpurea produces flowers with different colours ranging from red to white. ...
Tephrosia purpurea and T. villosa display vegetative growth and sexual reproduction throughout the year. T. purpurea produces resupinate and non-resupinate flowers with an explosive pollination mechanism, while T. villosa produces exclusively non-resupinate flowers with a valvular pollination mechanism. Flower-tripping is essential for the function of pollination mechanism and occurrence of self-or cross-pollination; tripping is effected by wind, rain, temperature, thrips, bees and wasps. Both species are facultatively xenogamous. Empty pods, ill-formed seeds and variation in the number of produced seeds has been attributed to the internal regulation by plants, in order to allow cross-pollinated flowers to produce more seeds and abort selectively the genetically inferior pollen resulting from self-pollination. The low fruit and seed set rates recorded in open-pollinated flowers of both Tephrosia species have been attributed to the presence of untripped flowers, extent of cross-pollination rate, short tenure of pollen viability, number of foraging visits made by pollinating insects, flower closure by the end of the day of anthesis, and availability of energy resources. Both species are autochorous, with short-range seed dispersal. Seeds germinate if the soil has moisture and nutrients but their continued growth and development is largely related to their efficiency in utilizing the available nutrients over other co-occurring seedlings or plants growing simultaneously with them. The plants also sprout from the perennial root stock, usually during rainy season. Therefore, the dual modes of propagation ensure these species' recolonizing of the same habitat and invading new habitats.
... Several pieces of evidence suggest that this transient LFY expression, already known to repress bracts (6), could also contribute to high-order meristem release. First, the outgrowth of otherwise inhibited axillary meristems in the rosette is stimulated by ectopic expression of LFY (or an LFY allele) (31,32). Second, it was established that the lfy ap1 cal triple mutant does not form cauliflowers (6), and we found that in this mutant, the number of high-order meristems was significantly reduced compared with ap1 cal (fig. ...
Vegetal fractals
Cauliflower, along with dahlias and daisies, develop as phyllotactic spirals. Azpeitia et al . combined modeling with experimental investigation to clarify the gene-regulatory network that sets up a multitude of undeveloped flowers to form a cauliflower curd. Irrepressible inflorescence identity genes in the context of dysfunctional meristems and slow internode elongation results in piles of incomplete flowers. If meristem size drifts during organogenesis, then the conical structures of the Romanesco form emerge in fractal formation. —PJH
The challenges facing tree orchard production in the coming years will be largely driven by changes in the climate affecting the sustainability of farming practices in specific geographical regions. Identifying key traits that enable tree crops to modify their growth to varying environmental conditions and taking advantage of new crop improvement opportunities and technologies will ensure the tree crop industry remains viable and profitable into the future. In this review article we 1) outline climate and sustainability challenges relevant to horticultural tree crop industries, 2) describe key tree crop traits targeted for improvement in agroecosystem productivity and resilience to environmental change, and 3) discuss existing and emerging genomic technologies that provide opportunities for industries to future proof the next generation of orchards.
Plant migration and gene flow from genetically-modified or exotic trees to nearby lands or by crossing with wild relatives is a major public and regulatory concern. Many genetic strategies exist to mitigate potential gene flow, however, the long delay in onset of flowering is a severe constraint to research progress. We used heat-induced-FT-overexpression to speed assessment of the expected floral phenotypes after CRISPR knockout of poplar homologs of the key floral genes, LEAFY and AGAMOUS. We selected events with previously characterized CRISPR-Cas9 induced biallelic changes then re-transformed them with the Arabidopsis thaliana FLOWERING LOCUS T (AtFT) gene under control of either a strong constitutive promoter or a heat-inducible promoter. We successfully obtained flowering in both a male and female clones of poplar, observing a wide range of inflorescence and floral forms among flowers, ramets, and insertion events. Overall, flowers obtained from the selected LFY and AG targeted events were consistent with what would be predicted for loss-of-function of these genes. LFY-targeted events showed small catkins with leaf-like organs, AG-targeted events had nested floral organs consistent with reduction in floral determinacy and absence of well-formed carpels or anthers. These findings demonstrate the great developmental plasticity of Populus flowers during genetically accelerated flowering, which may be of horticultural value. They also provide an informative early view of floral phenotypes and apparent sterility from knockouts of both these gene targets.
Continuously during their development, flowering plants produce a basic developmental unit:the phytomer. Canonical phytomers are composed of an internode and an axillary meristemsubtended by a leaf. The abrupt transition from vegetative to reproductive state remodels thecomposition of the phytomers. In most Brassicaceæ, including the model plant Arabidopsisthaliana, the reproductive phytomer looses its leaf, also called bract, producing a bractlesslateral floral meristem. However, production of flowers subtended by bracts have been reportedin specific environmental conditions, but only on the basal flowers of the inflorescence, producedduring floral transition. We show that in some natural accessions of Arabidopsis thaliana, suchbasal bract-flowers are common, yet not in the reference Col-0. Notably, in Tsu-0, bract-flowers are frequent regardless of environmental conditions. Moreover, contrary to what havebeen historically proposed, bract-flowers in Tsu-0 do not result from a conversion of branchesinto flowers. A transcriptomic analysis of shoot apices over floral transition in Tsu-0 andCol-0 reveals interesting heterochronies in the dynamic of gene expressions, although theirpotential link with bract production are still under investigation. To our knowledge, this studyfirst exposes the natural variations of transcriptomes from vegetative to flowering stages in A.thaliana. Notably, we show that gene expressions diverge the most precisely at the time offloral transition, recapitulating what have been previously described at an inter-species level.We also tried to map the genetic variations controlling bracts in Tsu-0 with both bulked F2segregant populations and Recombinants Inbred Lines. The genetic determinism of this trait iscomplex and we identified two major loci located in chromosome 1. We then crossed evidencefrom our genomic and transcriptomic data (including bract mutants) to propose some plausiblecandidate genes. From a particular case of natural variation, this study revisits the mechanismsthat control bract formation in A. thaliana and their links with floral transition. By extension,our results could also enlighten the evolutionary origin of bract loss in Brassicaceæ.
Flower initiation is a phenological developmental process strictly regulated in all flowering plants. Studies in Arabidopsis thaliana, a model plant organism in plant biology and genetics, and major cereal crops have provided fundamental knowledge and understanding of the underlying molecular mechanisms and regulation in annuals. However, this flowering process and underly molecular mechanisms in perennials are much more complicated than those in annuals and remain poorly understood and documented. In recent years, the increasing availability of perennial plant genomes and advances in biotechnology have allowed the identification and characterization of flowering-associated gene orthologs in perennials. In this review, we compared and summarized the recent progress in regulation of flowering time in perennial trees, with an emphasis on the perennial-specific regulatory mechanisms. Pleiotropic effects on tree growth habits such as juvenility, seasonal activity–dormancy growth, and the applications of tree flowering phenology are discussed.
The plant-specific transcription factor LEAFY (LFY), generally maintained as a single copy gene in most angiosperm species, plays critical roles in flower and leaf development. However, wild strawberry Fragaria vesca possesses four LFY homologues in the genome, their respective functions and evolution remain unknown. Through chemical mutagenesis screen, we identified two allelic mutations in one of the four LFY homologues, FveLFYa, in F. vesca, causing homeotic conversion of floral organs and reiterative outgrowth of ectopic florets. Both CRISPR-knockout and transgenic rescue confirmed the identity of FveLFYa. Ectopic expression of FveLFY homologues in Arabidopsis lfy-5 mutant revealed that only FveLFYa and FveLFYb can rescue the flower defects and induce solitary flowers in leaf axils. Disruption of FveLFYc, the second most abundantly expressed LFY homologue, caused no obvious morphology phenotypes in F. vesca. FveLFYb and FveLFYd are barely expressed. Expression of FveAP1, homologue of the well-known LFY target AtAP1, is not changed in the fvelfya flowers, possibly caused by an absence of any FveLFYa binding site in its promoter. Loss of Axillary Meristems encodes a GRAS transcription factor essential for stamen initiation. The ectopic florets are eliminated in fvelfya lam, suggesting that LAM is required for floret production. Moreover, approximately 30% of mature leaves have smaller or fewer leaflets in fvelfya. Among these homologues, only FveLFYa is syntenic to the homologues in other species. Overall, the detailed analyses of the four LFY homologues in woodland strawberry demonstrate that only FveLFYa plays crucial roles in floral patterning with rewired gene network.
Success in propagation of woody or tree species through conventional methods like cuttings is hindered due to the fact that cuttings in such species often fail to respond to rooting treatments. This failure to root is often linked to increased maturity (or decreased juvenility) in stem cuttings. To overcome from this situation, an alternative method of propagation has been used in tissue culture techniques (in vitro methods). In this technique, aseptic conditions are needed for culture of plant tissues (explants) and rapid mass propagation can be done in a limited space. Of the different in vitro methods, micrografting is an important and potential method to induce juvenility in tissues taken from mature plant, hence improving rooting efficiency in hardy or recalcitrant varieties. This chapter attempts to highlight the concept of juvenility and its significance in plant tissues culture, methods to induce juvenility, with special reference to micrografting and its significance in rooting in clonal propagation of elite tress species.
LEAFY (LFY) plays an important role in the flowering process of plants, controlling flowering time and mediating floral meristem differentiation. Owing to its considerable importance, the mango LFY gene (MiLFY; GenBank accession no. HQ585988) was isolated, and its expression pattern and function were characterized in the present study. The cDNA sequence of MiLFY was 1152 bp, and it encoded a 383 amino acid protein. MiLFY was expressed in all tested tissues and was highly expressed in flowers and buds. Temporal expression analysis showed that MiLFY expression was correlated with floral development stage, and two relative expression peaks were detected in the early stages of floral transition and floral organ differentiation. Moreover, 35S::GFP-MiLFY fusion protein was shown to be localized to the nucleus of cells. Overexpression of MiLFY in Arabidopsis promoted early flowering and the conversion of lateral meristems into terminal flowers. In addition, transgenic plants exhibited obvious morphological changes, such as differences in cauline leaf shape, and the number of lateral branches. When driven by the MiLFY promoter, GFP was highly expressed in leaves, floral organs, stems, and roots, during the flowering period. Exogenous gibberellin (GA3) treatment downregulated MiLFY promoter expression, but paclobutrazol (PPP333) upregulated it. Bimolecular fluorescence complementation (BiFC) assays showed that the MiLFY protein can interact with zinc-finger protein 4 (ZFP4) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (MiSOC1D). Taken together, these results indicate that MiLFY plays a pivotal role in controlling mango flowering, and that it is regulated by gibberellin and paclobutrazol.
Pyramidal-, erect- or upright-growing plant forms are characterized by narrow branch angles of shoots and leaves. The putative advantage of upright-leaf and shoot habit could be a more efficient penetration of light into lower canopy layers. Pyramidal genotypes have already been reported for various tree genotypes including peach. The paralogous rice ortholog TILLER ANGLE CONTROL 1 (TAC1) has been proposed to be the responsible gene for upright growth. However, it has not really been demonstrated for any of the pyramidal tree genotypes that a knock-out mutation of the TAC1 gene is causing pyramidal plant growth. By in silico analyses, we have identified a putative rice TAC1 ortholog (Potri.014G102600, “TAC-14”) and its paralog (Potri.002G175300, “TAC-2”) in the genome of P. trichocarpa. Two putative PcTAC1 orthologs in the P. × canescens clone INRA 717-1B4 were successfully knocked-out by applying a transgenic CRISPR/Cas9-approach. The mutants were molecularly analyzed and phenotyped over a period of three years in a glasshouse. Our results indicate that the homozygous knock-out of “TAC-14” is sufficient to induce pyramidal plant growth in P. × canescens. If up to twice as many pyramidal individuals were planted on short rotation coppices (SRCs), this could lead to higher wood yield, without any breeding, simply by increasing the number of trees on a default field size.
Flowering and juvenility are important traits for the cultivation and breeding of apples (Malus spp.). As apples are reported to have been cultivated long before ancient Greek civilization, many findings related to morphological and physiological traits, and well-developed cultivation techniques have been accumulated for many cultivated, ornamental, and rootstock apples. During the first half of the 1990s, elucidation of the molecular mechanism(s) of flower development in model plants has received much attention leading to major advances. This is followed by determinations of genetic sequences and functional analyses of genes controlling flowering and juvenility in these plants using genetic transformation technologies during the latter half of the 1990s. Subsequently, genes involved in floral organ development and genes involved in either flower induction or suppression of the apple, such as MdFT1 and MdTFL1, respectively, have been identified. Over the past decade, either stable or transient gene expression systems have been developed to control the flowering time in apple. These advances have had significant impacts on functional analysis of various genes of interest controlling fruit quality traits and pursuing apple breeding efforts with significantly reduced generation cycles. Future efforts should pursue functional analyses of genes, such as TFL1/FT-like genes; moreover, it is necessary to investigate and delineate relationships between plant hormones/sugars and flowering in apples.
Within the Arabidopsis inflorescence, two distinct developmental phases exist. The early inflorescence phase is characterized by nodes bearing coflorescences and leaves, and the late inflorescence phase by nodes bearing flowers. Four genes, TERMINAL FLOWER 1, LEAFY, APETALA1 and APETALA2 are necessary to initiate the switch from formation of early to formation of late inflorescence nodes at the appropriate time. We have investigated the relative roles of these genes in development by isolating and characterizing new alleles of TERMINAL FLOWER 1, LEAFY and APETALA1, and by constructing double mutants to test gene interactions. We suggest that the TERMINAL FLOWER 1 gene product is part of a mechanism that controls the timing of phase- switching in Arabidopsis. We propose that this mechanism involves factor(s) whose activity changes in response to shoot development and environmental variation. TERMINAL FLOWER 1 influences phase transitions in Arabidopsis, and appears to regulate the timing of expression of LEAFY, APETALA1 and APETALA2. LEAFY, APETALA1 and APETALA2 have partially redundant functions in initiating the floral program. In the absence of any one of the three genes, there is a gradual transition from coflorescence to flower-like lateral shoots. This suggests that (1) LEAFY, APETALA1 and APETALA2 are required in combination to ensure that the floral program is initiated rapidly and completely and (2) in the absence of one of the three genes, the others are activated slowly in response to the mechanism controlling timing of phase switching. Besides their role in establishing the floral program, phenotypes of flower-like lateral shoots in mutant inflorescences suggest that all three, LEAFY, APETALA1 and APETALA2, influence expression of whorl identity genes. Loss of LEAFY results in decreased Class B gene expression, as well as altered expression patterns of Class A and Class C genes. In the absence of either APETALA2 or APETALA1, reproductive organs develop in the perianth whorls, suggesting that both genes should be considered Class A organ identity genes, restricting Class C gene expression to inner whorls.
Containment of transgenes inserted into genetically engineered forest trees will probably be necessary before most commercial uses are possible. This is a consequence of (1) high rates of gene dispersal by pollen and seed, (2) proximity of engineered trees in plantations to natural or feral stands of interfertile species, and (3) potentially undesirable ecological effects if certain transgenes become widely dispersed. In addition to gene containment, engineering of complete or male sterility may stimulate faster wood production, reduce production of allergenic pollen, and facilitate hybrid breeding. We review the regulatory and ecological rationale for engineering sterility, potentially useful floral genes, strategies for creating sterility-causing transgenes, and problems peculiar to engineering sterility in forest trees. Each of the two primary options — ablating floral tissuesvia floral promoter-cytotoxin fusions, and disrupting expression of essential floral genes by various methods of gene suppression — has advantages and disadvantages. Because promoters from structural and enzymatic floral-specific genes often work well in heterologous species, ablation methods based on these genes probably will not require cloning of homologs from angiosperm trees. Methods that inhibit gene expression will require cloning of tree genes and may be more prone to epigenetic variability, but should allow assay of transgene efficacy in seedlings. Practical constraints include the requirement for vegetative propagation if complete sterility is engineered and the need for highly stable forms of sterility in long-lived trees. The latter may require suppression of more than one floral gene or employment of more than one genetic mechanism for sterility.
Growth of flowering stems in wild-type Arabidopsis is indeterminate. Many flowers arise sequentially on the flanks of apical meristems in a phyllotactic spiral. We have isolated eight recessive mutants of a gene, terminal flower, in which inflorescences become determinate. Flower primordia sooner or later ‘invade’ the meristem summit leading to cessation of its further growth. Primary apical meristems usually terminate with several part-flowers which lack pedicels, and several normal pedicellate flowers may arise first. By contrast apical meristems of secondary branches usually produce only a single pedicellate flower. Plant height is also reduced and more rosette inflorescences develop. These growth patterns occur in six strong mutants raised at 25°C under continuous light. In two weak mutants termination occurs much later with many more flowers arising before eventual termination. Termination is similarly delayed in at least one of the strong mutants grown at lower temperatures. The tfl mutation does not affect the indeterminate growth of flower meristems, at least in-so-far as this occurs in agamous mutants. The tfl locus is at the top of linkage group 5, close to RFLP 447.
We propose that the TFL gene product supports the activity of an inhibitor of flower primordium initiation. This inhibitor would normally prevent flowers from arising on the inflorescence apex but in tfl mutants it may readily fall below its threshold of activity. The TFL gene may be one of a class responsible for evolutionary changes between indeterminate and determinate growth.
Mutations in the APETALA1 gene disturb two phases of flower development, flower meristem specification and floral organ specification. These effects become manifest as a partial conversion of flowers into inflorescence shoots and a disruption of sepal and petal development. We describe the changes in an allelic series of nine apetala1 mutants and show that the two functions of APETALA1 are separable. We have also studied the interaction between APETALA1 and other floral genes by examining the phenotypes of multiply mutant plants and by in situ hybridization using probes for several floral control genes. The results suggest that the products of APETALA1 and another gene, LEAFY, are required to ensure that primordia arising on the flanks of the inflorescence apex adopt a floral fate, as opposed to becoming an inflorescence shoot. APETALA1 and LEAFY have distinct as well as overlapping functions and they appear to reinforce each other's action. CAULIFLOWER is a newly discovered gene which positively regulates both APETALA1 and LEAFY expression. All functions of CAULIFLOWER are redundant with those of APETALA1. APETALA2 also has an early function in reinforcing the action of APETALA1 and LEAFY, especially if the activity of either is compromised by mutation. After the identity of a flower primordium is specified, APETALA1 interacts with APETALA2 in controlling the development of the outer two whorls of floral organs.
The first step in flower development is the generation of a floral meristem by the inflorescence meristem. We have analyzed how this process is affected by mutant alleles of the Arabidopsis gene LEAFY. We show that LEAFY interacts with another floral control gene, APETALA1, to promote the transition from inflorescence to floral meristem. We have cloned the LEAFY gene, and, consistent with the mutant phenotype, we find that LEAFY RNA is expressed strongly in young flower primordia. LEAFY expression procedes expression of the homeotic genes AGAMOUS and APETALA3, which specify organ identify within the flower. Furthermore, we demonstrate that LEAFY is the Arabidopsis homolog of the FLORICAULA gene, which controls floral meristem identity in the distantly related species Antirrhinum majus.
We have characterized the floral phenotypes produced by the recessive homeotic apetala 1-1 (ap1-1) mutation in Arabidopsis. Plants homozygous for this mutation display a homeotic conversion of sepsis into brachts and the concomitant formation of floral buds in the axil of each transformed sepal. In addition, these flowers lack petals. We show that the loss of petal phenotype is due to the failure of petal primordia to be initiated. We have also constructed double mutant combinations with ap1 and other mutations affecting floral development. Based on these results, we suggest that the AP1 and the apetala 2 (AP2) genes may encode similar functions that are required to define the pattern of where floral organs arise, as well as for determinate development of the floral meristem. We propose that the AP1 and AP2 gene products act in concert with the product of the agamous (AG) locus to establish a determinate floral meristem, whereas other homeotic gene products are required for cells to differentiate correctly according to their position. These results extend the proposed role of the homeotic genes in floral development and suggest new models for the establishment of floral pattern.
We describe the role of the UNUSUAL FLORAL ORGANS (UFO) gene in Arabidopsis floral development based on a genetic and molecular characterization of the phenotypes of nine ufo alleles. UFO is required for the proper identity of the floral meristem and acts in three different aspects of the process that distinguishes flowers from shoots. UFO is involved in establishing the whorled pattern of floral organs, controlling the determinacy of the floral meristem, and activating the APETALA3 and PISTILLATA genes required for petal and stamen identity. In many respects, UFO acts in a manner similar to LEAFY, but the ufo mutant phenotype also suggests an additional role for UFO in defining boundaries within the floral primordia or controlling cell proliferation during floral organ growth. Finally, genetic interactions that prevent flower formation and lead to the generation of filamentous structures implicate UFO as a member of a new, large, and diverse class of genes in Arabidopsis necessary for flower formation.
In the leafy mutant of Arabidopsis, most of the lateral meristems that are fated to develop as flowers in a wild-type plant develop as inflorescence branches, whereas a few develop as abnormal flowers consisting of whorls of sepals and carpels. We have isolated several new alleles of leafy and constructed a series of double mutants with leafy and other homeotic mutants affecting floral development to determine how these genes interact to specify the developmental fate of lateral meristems. We found that leafy is completely epistatic to pistillata and interacts additively with agamous in early floral whorls, whereas in later whorls leafy is epistatic to agamous. Double mutants with leafy and either apetala1 or apetala2 showed a complete loss of the whorled phyllotaxy, shortened internodes, and suppression of axillary buds typical of flowers. Our results suggest that the products of LEAFY, APETALA1, and APETALA2 together control the differentiation of lateral meristems as flowers rather than as inflorescence branches.
Variation in plant shoot structure may be described as occurring through changes within a basic unit, the metamer. Using this terminology, the apical meristem of Arabidopsis produces three metameric types sequentially: type 1, rosette; type 2, coflorescence-bearing with bract; and type 3, flower-bearing without bract. We describe a mutant of Arabidopsis, Leafy, homozygous for a recessive allele of a nuclear gene LEAFY (LFY), that has an inflorescence composed only of type 2-like metamers. These data suggest that the LFY gene is required for the development of type 3 metamers and that the transition from type 2 to type 3 metamers is a developmental step distinct from that between vegetative and reproductive growth (type 1 to type 2 metamers). Results from double mutant analysis, showing that lfy-1 is epistatic to the floral organ homeotic gene ap2-6, are consistent with the hypothesis that a functional LFY gene is necessary for the expression of downstream genes controlling floral organ identity.
APETALA2 (AP2) plays a central role in the establishment of the floral meristem, the specification of floral organ identity, and the regulation of floral homeotic gene expression in Arabidopsis. We show here that in addition to its functions during flower development, AP2 activity is also required during seed development. We isolated the AP2 gene and found that it encodes a putative nuclear protein that is distinguished by an essential 68-amino acid repeated motif, the AP2 domain. Consistent with its genetic functions, we determined that AP2 is expressed at the RNA level in all four types of floral organs--sepals, petals, stamens, and carpels--and in developing ovules. Thus, AP2 gene transcription does not appear to be spatially restricted by the floral homeotic gene AGAMOUS as predicted by previous studies. We also found that AP2 is expressed at the RNA level in the inflorescence meristem and in nonfloral organs, including leaf and stem. Taken together, our results suggest that AP2 represents a new class of plant regulatory proteins that may play a general role in the control of Arabidopsis development.
Grafting experiments were used to investigate the relative roles of strength of flowering signal(s) and competence of buds to respond to flowering signal(s) in the development of photoperiodic and day-neutral species of Nicotiana. At the time of commitment to floral development, a flowering signal (inhibitory or promotive) could reach a critical level or terminal buds could gain competence to perceive and-or respond to an existing signal. The latter hypothesis appears to be true for day-neutral N. tabacum L. cv. Wisconsin 38, while signal strength appears to be a more critical factor for long-day N. silvestris L. Nicotiana tabacum and N. silvestris differ in terms of signal intensity at anthesis of the terminal flower. Stocks of N. silvestris promote more rapid flowering in seedling scions of both genotypes. Terminal buds of seedlings of both genotypes have the same competence to respond to the signal affecting floral development. The competence of the terminal bud of both species to respond to this signal(s) changes as a function of age.
The mantle can be sampled directly only very rarely. Geochemists have
thus come to rely heavily on mantle-derived magmas to study the
composition and evolution of the mantle. Only those compositional
features that are unaffected by magmatic processes are useful as tracers
of mantle processes. These include radiogenic isotope ratios such as
those of He, Sr, Hf, and Os, stable isotope ratios, and ratios of highly
incompatible elements or elements of similar incompatibility, such as
Ba/Nb or Pb/Ce. The term "incompatible" denotes a preference of the
element for a melt over mantle minerals. Highly incompatible elements
will partition entirely into the melt under most circumstances, so that
the ratio of two such elements in a basalt will be virtually identical
to that ratio in its source. This is also true to a lesser degree of
ratios such as La/Sm and Zr/Nb, as Zr and Sm are not highly incompatible
elements.
Breeders have traditionally improved plant varieties by selecting on the basis of phenotype. Now restriction fragment length polymorphism (RFLP) linkage maps are being constructed for most major crop plants and these maps provide a more direct method for selecting desirable genes via their linkage to easily detectable RFLP markers. The integration of RFLP techniques into plant breeding promises to: (1) Expedite the movement of desirable genes among varieties, (2) Allow the transfer of novel genes from related wild species, (3) Make possible the analysis of complex polygenic characters as ensembles of single Mendelian factors, and (4) Establish genetic relationships between sexually incompatible crop plants. In the future, high density RFLP maps may also make it possible to clone genes whose products are unknown, such as genes for disease resistance or stress tolerance.
A protocol has been developed for efficiently transforming and regenerating the hybrid aspenPopulus tremula x P. tremuloides. Stem segments were co-cultivated with a strain ofAgrobacterium tumefaciens carrying a disarmed binary vector conferring resistance to kanamycin or hygromycin. The respective vectors also carried a
fused bacterialluxF2 gene expressed from the cauliflower mosaic virus 35S promoter. All transformants had a normal phenotype. Genetic tranformation
and stable integration of the heterologous DNA was confirmed by Southern hybridization and luciferase expression. The latter
was measured by destructive enzymatic assay throughout the transformatnt and by non-destructive image analysis in leaves left
attached to intact plants. Both measurement techniques detected marked within- and between-organ variation in luciferase expression.
However, the spatial patterns detected by each technique in the leaves were similar. The results indicate thatin vivo imaging of light emission can be used to measure repeatedly the expression of a promoter-luciferase gene fusion in a particular
leaf over an extended time period. It was also demonstrated that enzymatically assayed luciferase activity in leaves was notably
lowere in transgenic hybrid aspen plants than in tobacco plants transformed with the same vector. This was not due to a difference
in luciferase enzyme activity between the two species, and therefore indicated that the 35S promoter is not as active in hybrid
aspen as in tobacco.
Floral initiation can be analyzed from a developmental perspective by focusing upon how developmental fates are imprinted, remembered, and expressed. This is not an altogether new perspective, since people studying flowering have been concerned for a long time with the commitment of meristems to form flowers and the morphological, cellular, and molecular changes associated with this commitment. What is novel is the emphasis on developmental states as opposed to physiological processes. This developmental focus indicates that there appear to be at least three major developmental states that are acquired and expressed in the process of a meristem initiating floral morphogenesis. The meristem cells must first become competent to respond to a developmental signal that evokes them into a florally determined state. The leaves are the usual source of this signal and a specific leaf may or may not have the capacity to be inductively active. When a leaf does develop the capacity for inductive activity, this capacity is usually correlated with the ontogeny of the leaf. Inductive activity, however, may be continually expressed as in some day-neutral plants or may be latent as in plants where the photoperiod is the external cue for activity. Competent shoot apical meristems respond to inductive leaf signal by being evoked into a florally determined state. Under permissive conditions this florally determined state is expressed as the initiation of floral morphogenesis. Many mechanisms have evolved to regulate entry into and expression of these developmental states. As we learn more about the developmental states associated with flowering and how they are acquired and expressed, we will understand better how the various patterns of flowering are related to one another as well as which developmental processes are common to all angiosperms.
The first step in flower development is the transition of an inflorescence meristem into a floral meristem. Each floral meristem differentiates into a flower consisting of four organ types that occupy precisely defined positions within four concentric whorls. Genetic studies in Arabidopsis thaliana and Antirrhinum majus have identified early-acting genes that determine the identify of the floral meristem, and late-acting genes that determine floral organ identity. In Arabidopsis, at least two genes, APETALA1 and LEAFY, are required for the transition of an influorescence meristem into a floral meristem. We have cloned the APETALA1 gene and here we show that it encodes a putative transcription factor that contains a MADS-domain. APETALA1 RNA is uniformly expressed in young flower primordia, and later becomes localized to sepals and petals. Our results suggest that APETALA1 acts locally to specify the identity of the floral meristem, and to determine sepal and petal development.
There are marked differences in the pattern of host gene expression in incompatible plant:microbial pathogen interactions compared with compatible interactions, associated with the elaboration of inducible defenses. Constitutive expression of genes encoding a chitinase or a ribosome-inactivating protein in transgenic plants confers partial protection against fungal attack, and a large repertoire of such antimicrobial genes has been identified for further manipulation. In addition, strategies are emerging for the manipulation of multigenic defenses such as lignin deposition and synthesis of phytoalexin antibiotics by overexpression of genes encoding rate determining steps, modification of transcription factors or other regulatory genes, and engineering production of novel phytoalexins by interspecies transfer of biosynthetic genes. The imminent cloning of disease resistance genes, further molecular dissection of stress signal perception and transduction mechanisms, and identification of genes that affect symptom development will provide attractive new opportunities for enhancing crop protection. Combinatorial integration of these novel strategies into ongoing breeding programs should make an important contribution to effective, durable field resistance.
Although promoter regions for many plant nuclear genes have been sequenced, identification of the active promoter sequence has been carried out only for the octopine synthase promoter. That analysis was of callus tissue and made use of an enzyme assay. We have analysed the effects of 5' deletions in a plant viral promoter in tobacco callus as well as in regenerated plants, including different plant tissues. We assayed the RNA transcription product which allows a more direct assessment of deletion effects. The cauliflower mosaic virus (CaMV) 35S promoter provides a model plant nuclear promoter system, as its double-strand DNA genome is transcribed by host nuclear RNA polymerase II from a CaMV minichromosome. Sequences extending to -46 were sufficient for accurate transcription initiation whereas the region between -46 and -105 increased greatly the level of transcription. The 35S promoter showed no tissue-specificity of expression.
The homologous genes FLORICAULA (FLO) of Antirrhinum and LEAFY (LFY) of Arabidopsis regulate the formation of determinate floral meristems. Transcripts of these single-copy genes are confined to floral meristems and some floral organs as well as to the leaflike bracts that subtend Antirrhinum flowers. Based on these observations, we hypothesized that the transcription of genes homologous to FLO and LFY in tobacco, a determinate plant in which the primary shoot apex is consumed in the production of a terminal flower, would serve as a molecular marker for floral commitment. Surprisingly, transcripts of the tobacco homologs NFL1 and NFL2 (Nicotiana FLO/LFY) were found not only in floral meristems, but also in indeterminate vegetative meristems. This implies that the transcriptional expression of the FLO/LFY homologous genes in the apical meristem is not sufficient for the initiation of floral meristem development. In addition, the transcript patterns of the NFL genes identified a previously undescribed subset of cells within the shoot apical meristem that may indicate unique functional compartmentalization. This suggests that, unlike FLO and LFY, which specify determinacy only during floral development, the NFL genes act to specify determinacy in the progenitor cells for both flowers and leaves.
Genetic studies demonstrate that two Arabidopsis genes, CAULIFLOWER and APETALA1, encode partially redundant activities involved
in the formation of floral meristems, the first step in the development of flowers. Isolation of the CAULIFLOWER gene from
Arabidopsis reveals that it is closely related in sequence to APETALA1. Like APETALA1, CAULIFLOWER is expressed in young flower
primordia and encodes a MADS-domain, indicating that it may function as a transcription factor. Analysis of the cultivated
garden variety of cauliflower (Brassica oleracea var. botrytis) reveals that its CAULIFLOWER gene homolog is not functional,
suggesting a molecular basis for one of the oldest recognized flower abnormalities.
APETALA3 (AP3) specifies the development of petals and stamens in the Arabidopsis flower. We constructed a transgenic line, 35S-AP3, that ectopically expresses AP3 under the control of a constitutive promoter. The resulting flowers exhibit a replacement of carpels by stamens and resemble flowers homozygous for the previously described Arabidopsis mutation superman. Although AP3 RNA is detected at high levels throughout the flower and stem in 35S-AP3, AP3 protein is detected at high levels only in the second, third, and fourth floral whorls, demonstrating that AP3 is posttranscriptionally regulated. Ectopic expression of AP3 causes a second floral homeotic gene, PISTILLATA (PI), to function in the fourth whorl of 35S-AP3 flowers. AP3 and PI also activate an AP3 promoter-reporter gene fusion, demonstrating that AP3 positively autoregulates.
Flower development consists of several phases. The first step is the transition from vegetative to reproductive development, regulated by floral induction. Later steps include the initiation of individual flowers, the determination of organ identity, and organ-specific differentiation. One of the major discoveries of plant biology is that the genetic network controlling flower development is highly conserved in two distantly related dicots, Arabidopsis thaliana and Antirrhinum majus, and probably in other species as well. Classical genetics has identified a sizable number of genes regulating flower development, and many of these regulatory genes have been cloned. This review summarizes recent advances in the understanding of the genetic control of floral induction and determination of flower-meristem identity, with the focus on Arabidopsis thaliana. In addition, recent work on ovule morphogenesis, a late process in flower development, is discussed.
Several aspects of the photophysiology of wild-type Arabidopsis thaliana seedlings were compared with those of a phytochrome A null mutant, phyA-1, and a mutant, fhy1, that is putatively involved in the transduction of light signals from phytochrome A. Although phyA seedlings display a near wild-type phenotype when grown in white light (W), they nevertheless display several photomorphogenic abnormalities. Thus, whereas the germination of wild-type and fhy1 seeds is almost fully promoted by a pulse of red light (R) or by continuous far-red light (FR), phyA seed germination is responsive only to R. Following growth under day/night cycles, but not under continuous W, the hypocotyls of light-grown phyA and fhy1 seedlings are more elongated than those of wild-type seedlings. For seedlings grown under low red/far-red (R/FR) ratio light conditions, phyA and fhy1 seedlings display a more marked promotion of hypocotyl elongation than wild-type seedlings. Similarly, seedlings that are doubly null for phytochrome A and phytochrome B(phyA phyB) also have more elongated hypocotyls under low R/FR ratio conditions than phyB seedlings. This indicates that phytochrome A action in light-grown seedlings is antagonistic to the action of phytochrome B. Although wild-type, fhy1, and phyA seedlings flower at essentially the same time under both short-day and long-day conditions, an obvious consequence of phytochrome A deficiency is a pronounced late flowering under conditions where a short day of 8 h of fluorescent W is extended by 8 h of low-fluence-rate incandescent light. The evidence thus indicates that phytochrome A plays a role in seed germination, in the control of elongation growth of light-grown seedlings, and in the perception of daylength.
Plant responses to red and far-red light are mediated by a family of photoreceptors called phytochromes. In Arabidopsis thaliana, there are genes encoding at least five phytochromes, and it is of interest to learn if the different phytochromes have overlapping or distinct functions. To address this question for two of the phytochromes in Arabidopsis, we have compared light responses of the wild type with those of a phyA null mutant, a phyB null mutant, and a phyA phyB double mutant. We have found that both phyA and phyB mutants have a deficiency in germination, the phyA mutant in far-red light and the phyB mutant in the dark. Furthermore, the germination defect caused by the phyA mutation in far- red light could be suppressed by a phyB mutation, suggesting that phytochrome B (PHYB) can have an inhibitory as well as a stimulatory effect on germination. In red light, the phyA phyB double mutant, but neither single mutant, had poorly developed cotyledons, as well as reduced red-light induction of CAB gene expression and potentiation of chlorophyll induction. The phyA mutant was deficient in sensing a flowering response inductive photoperiod, suggesting that PHYA participates in sensing daylength. In contrast, the phyB mutant flowered earlier than the wild type (and the phyA mutant) under all photoperiods tested, but responded to an inductive photoperiod. Thus, PHYA and PHYB appear to have complementary functions in controlling germination, seedling development, and flowering. We discuss the implications of these results for possible mechanisms of PHYA and PHYB signal transduction.
In Arabidopsis, floral meristems arise in continuous succession directly on the flanks of the inflorescence meristem. Thus, the pathways that regulate inflorescence and floral meristem identity must operate both simultaneously and in close spatial proximity. The TERMINAL FLOWER 1 (TFL1) gene of Arabidopsis is required for normal inflorescence meristem function, and the LEAFY (LFY), APETALA 1 (AP1), and APETALA 2 (AP2) genes are required for normal floral meristem function. We present evidence that inflorescence meristem identity is promoted by TFL1 and that floral meristem identity is promoted by parallel developmental pathways, one defined by LFY and the other defined by AP1/AP2. Our analysis suggests that the acquisition of meristem identity during inflorescence development is mediated by antagonistic interactions between TFL1 and LFY and between TFL1 and AP1/AP2. Based on this study, we propose a simple model for the genetic regulation of inflorescence development in Arabidopsis. This model is discussed in relation to the proposed interactions between the inflorescence and the floral meristem identity genes and in regard to other genes that are likely to be part of the genetic hierarchy regulating the establishment and maintenance of inflorescence and floral meristems.
We present the initial phenotypic characterization of an Arabidopsis mutation, terminal flower 1-1 (tfl1-1), that identifies a new genetic locus, TFL1. The tfl1-1 mutation causes early flowering and limits the development of the normally indeterminate inflorescence by promoting the formation of a terminal floral meristem. Inflorescence development in mutant plants often terminates with a compound floral structure consisting of the terminal flower and one or two subtending lateral flowers. The distal-most flowers frequently contain chimeric floral organs. Light microscopic examination shows no structural aberrations in the vegetative meristem or in the inflorescence meristem before the formation of floral buttresses. The wild-type appearance of lateral flowers and observations of double mutant combinations of tfl1-1 with the floral morphogenesis mutations apetala 1-1 (ap1-1), ap2-1, and agamous (ag) suggest that the tfl1-1 mutation does not affect normal floral meristems. Secondary flower formation usually associated with the ap1-1 mutation is suppressed in the terminal flower, but not in the lateral flowers, of tfl1-1 ap1-1 double mutants. Our results suggest that tfl1-1 perturbs the establishment and maintenance of the inflorescence meristem. The mutation lies on the top arm of chromosome 5 approximately 2.8 centimorgans from the restriction fragment length polymorphism marker 217.
The identity of floral organs in Arabidopsis thaliana is determined by homeotic genes, which are expressed in specific regions of the developing flower. The initial activation
of homeotic genes is accomplished at least in part by the products of two earlier acting genes with overlapping functions.
These are the floral meristem—identity genes LEAFY and APETALA1. The requirements of LEAFY and APETALA1 activity vary for different homeotic genes.
USDA Agriculture Handbook 450: Seeds of Woody Plants in the United States
- E. J. Schreiner
- J L Bowman
- J Alvarez
- D Weigel
- E M Meyerowitz
- D R Smyth
- JL Bowman