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Schematic diagrams of the Petunia hybrida wild-type flower (V26). (Left) A longitudinal section illustrating the fusion of the stamen filaments to the corolla tube and the faces on which trichomes can be detected. CF (congenital fusion) indicates the region where the stamen filament is fused to the corolla tube. (Se) Sepal; (Li} corolla Limb; (Tu) corolla Tube; (An) anther; (St) style and Stigma; (Ov} ovary. (Right) Floral diagram. (Se) Sepal;, (Pe) petal; (St) stamen; (Ca) carpel.
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The petunia mutant green petal (gp, line PLV) shows a homeotic effect in one floral whorl, that is, the conversion of petal to sepal. We demonstrate that this mutant contains a chromosomal deletion, including the petunia MADS box gene pMADS1. Second whorl petal development in this null mutant can be restored with a CaMV 35S-pMADS1 transgene, demons...
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... in the calyx tube contain cells that make less chlorophyll, as judged from the white color of the parenchyma cells. Growth of the corolla tube and of the filaments occurs in part under the zone of interpetalous initiation, resulting in congenital fusion of the filaments to the corolla tube ( Figs. 1 and 2C). Figure 2D shows a stained cross section near the base of a 10-mm-long floral bud illustrating the fusion of the filament to the tube. ...
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... flowers not only help to define the function of pMADS1 but also to analyze the actual process of petal growth and differentiation in petunia. Figure 10A shows the different end stages of second whorl organ develop- ment, starting with the gp sepal [ Fig. 10A(1 )], V26 partial cosuppression [ Fig. 10A(2) and (3)], gp partial restoration, and ending with wild-type petal. Similar end stages of petal development are shown schematically in Figure 10B. ...
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... (PLV), we created a series of (mature) flowers with different stages of petal development. These flowers not only help to define the function of pMADS1 but also to analyze the actual process of petal growth and differentiation in petunia. Figure 10A shows the different end stages of second whorl organ develop- ment, starting with the gp sepal [ Fig. 10A(1 )], V26 partial cosuppression [ Fig. 10A(2) and (3)], gp partial restoration, and ending with wild-type petal. Similar end stages of petal development are shown schematically in Figure 10B. The petal differentiation in the epidermal cell layer suppresses trichome and stomata formation and pro- motes longitudinal and lateral cell ...
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... with different stages of petal development. These flowers not only help to define the function of pMADS1 but also to analyze the actual process of petal growth and differentiation in petunia. Figure 10A shows the different end stages of second whorl organ develop- ment, starting with the gp sepal [ Fig. 10A(1 )], V26 partial cosuppression [ Fig. 10A(2) and (3)], gp partial restoration, and ending with wild-type petal. Similar end stages of petal development are shown schematically in Figure 10B. The petal differentiation in the epidermal cell layer suppresses trichome and stomata formation and pro- motes longitudinal and lateral cell divisions in the tube and the limb. The fully ...
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... 10A shows the different end stages of second whorl organ develop- ment, starting with the gp sepal [ Fig. 10A(1 )], V26 partial cosuppression [ Fig. 10A(2) and (3)], gp partial restoration, and ending with wild-type petal. Similar end stages of petal development are shown schematically in Figure 10B. The petal differentiation in the epidermal cell layer suppresses trichome and stomata formation and pro- motes longitudinal and lateral cell divisions in the tube and the limb. ...
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... growth patterns that transform a sepaloid organ into a petal are illustrated in Figure 10C. The sepal growth (S; Fig. 10C) includes a congenital fusion at the base of the five sepaloid organs, leading to a tube struc- ture. ...
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... growth patterns that transform a sepaloid organ into a petal are illustrated in Figure 10C. The sepal growth (S; Fig. 10C) includes a congenital fusion at the base of the five sepaloid organs, leading to a tube struc- ture. This tube structure corresponds to the fused part of the corolla limb; the corolla tube has no real equivalent in gp (see below). When the petal differentiation pathway is activated, S growth is transformed into C growth (Fig. 10C) and ...
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... sepal growth (S; Fig. 10C) includes a congenital fusion at the base of the five sepaloid organs, leading to a tube struc- ture. This tube structure corresponds to the fused part of the corolla limb; the corolla tube has no real equivalent in gp (see below). When the petal differentiation pathway is activated, S growth is transformed into C growth (Fig. 10C) and extended by additional lateral cell divisions (Fig. 10C, C1), additional longitudinal cell divisions at the base, which make up a part of the corolla tube (Fig. 10C, C2), and additional cell divisions under the base of the sepal and the stamen (Fig. 10C, C3 and F2), which make up the part of the corolla tube with the fused sta- ...
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... base of the five sepaloid organs, leading to a tube struc- ture. This tube structure corresponds to the fused part of the corolla limb; the corolla tube has no real equivalent in gp (see below). When the petal differentiation pathway is activated, S growth is transformed into C growth (Fig. 10C) and extended by additional lateral cell divisions (Fig. 10C, C1), additional longitudinal cell divisions at the base, which make up a part of the corolla tube (Fig. 10C, C2), and additional cell divisions under the base of the sepal and the stamen (Fig. 10C, C3 and F2), which make up the part of the corolla tube with the fused sta- men filaments. The C3 and F2 growth are affected most easily by ...
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... part of the corolla limb; the corolla tube has no real equivalent in gp (see below). When the petal differentiation pathway is activated, S growth is transformed into C growth (Fig. 10C) and extended by additional lateral cell divisions (Fig. 10C, C1), additional longitudinal cell divisions at the base, which make up a part of the corolla tube (Fig. 10C, C2), and additional cell divisions under the base of the sepal and the stamen (Fig. 10C, C3 and F2), which make up the part of the corolla tube with the fused sta- men filaments. The C3 and F2 growth are affected most easily by pMADS1 cosuppression and restored least eas- ily by pMADS1 expression in gp (PLV) plants. Under con- ditions of ...
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... the petal differentiation pathway is activated, S growth is transformed into C growth (Fig. 10C) and extended by additional lateral cell divisions (Fig. 10C, C1), additional longitudinal cell divisions at the base, which make up a part of the corolla tube (Fig. 10C, C2), and additional cell divisions under the base of the sepal and the stamen (Fig. 10C, C3 and F2), which make up the part of the corolla tube with the fused sta- men filaments. The C3 and F2 growth are affected most easily by pMADS1 cosuppression and restored least eas- ily by pMADS1 expression in gp (PLV) plants. Under con- ditions of partial cosuppression (SD 15a) or partial resto- ration (Mlb) of the pMADS1 function, the tube ...
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... men filaments. The C3 and F2 growth are affected most easily by pMADS1 cosuppression and restored least eas- ily by pMADS1 expression in gp (PLV) plants. Under con- ditions of partial cosuppression (SD 15a) or partial resto- ration (Mlb) of the pMADS1 function, the tube and fil- ament growth only occurs above the petal and stamen initiation zone (Fig. 10C, C2 and F1), resulting in sepa- rate (nonfused) stamen filaments and corolla tube. The differentiation of the sepaloid second whorl organ into petal is mainly responsible for the corolla limb structure (Fig. 10C, C and C1). This is, for instance, illustrated by flowers of Mlb (Fig. 7D, G, H), which show petal tissue (C1 growth) at the fringes of ...
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... resto- ration (Mlb) of the pMADS1 function, the tube and fil- ament growth only occurs above the petal and stamen initiation zone (Fig. 10C, C2 and F1), resulting in sepa- rate (nonfused) stamen filaments and corolla tube. The differentiation of the sepaloid second whorl organ into petal is mainly responsible for the corolla limb structure (Fig. 10C, C and C1). This is, for instance, illustrated by flowers of Mlb (Fig. 7D, G, H), which show petal tissue (C1 growth) at the fringes of the otherwise sepaloid sec- ond whorl organs, and in flowers of Mlc (Fig. 7I), where the sepaloid structure that forms in gp (PLV) flowers can still be seen within the corolla limb that has formed by pMADS1 ...
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... of Mlb (Fig. 7D, G, H), which show petal tissue (C1 growth) at the fringes of the otherwise sepaloid sec- ond whorl organs, and in flowers of Mlc (Fig. 7I), where the sepaloid structure that forms in gp (PLV) flowers can still be seen within the corolla limb that has formed by pMADS1 restoration. The corolla tube is formed by C2 and C3 growth (Fig. 10C), and equivalent growth is either extremely limited or absent in the sepaloid organs of ...
Similar publications
Genetic studies in Arabidopsis and Antirrhinum showed that petal determination requires the concomitant expression of two homeotic functions, A and B, whereas the A function alone determines sepal identity. The B function is represented by at least two genes. The Petunia homeotic gene green petal (gp) is essential for petal determination as demonst...
Several homeotic genes controlling floral development have been isolated in both Antirrhinum and Arabidopsis. Based on the similarities in sequence and in the phenotypes elicited by mutations in some of these genes, it has been proposed that the regulatory hierarchy controlling floral development is comparable in these two species. We have performe...
Citations
... Indeed, B-class mutants in eudicots usually show a phenotype affecting both the petal and stamen whorls and converting them into sepals and carpels respectively; this is for instance the case in tomato when the APETALA3 (AP3) ortholog STAMENLESS is knocked-out [39,40]. However, the situation is different in petunia: mutant in the B-class gene PhDEFICIENS (PhDEF), also known as green petals, has a full conversion of petals into sepals, but stamens remain unaffected [41]. PhDEF is expressed in petal and stamen primordia, suggesting that another gene redundantly controls stamen identity [42]. ...
Flower development is the process leading from a reproductive meristem to a mature flower with fully developed floral organs. This multi-step process is complex and involves thousands of genes in intertwined regulatory pathways; navigating through the FLOR-ID website will give an impression of this complexity and of the astonishing amount of work that has been carried on the topic (Bouché et al., Nucleic Acids Res 44:D1167-D1171, 2016). Our understanding of flower development mostly comes from the model species Arabidopsis thaliana, but numerous other studies outside of Brassicaceae have helped apprehend the conservation of these mechanisms in a large evolutionary context (Moyroud and Glover, Curr Biol 27:R941-R951, 2017; Smyth, New Phytol 220:70-86, 2018; Soltis et al., Ann Bot 100:155-163, 2007). Integrating additional species and families to the research on this topic can only advance our understanding of flower development and its evolution.In this chapter, we review the contribution that the Solanaceae family has made to the comprehension of flower development. While many of the general features of flower development (i.e., the key molecular players involved in flower meristem identity, inflorescence architecture or floral organ development) are similar to Arabidopsis, our main objective in this chapter is to highlight the points of divergence and emphasize specificities of the Solanaceae. We will not discuss the large topics of flowering time regulation, inflorescence architecture and fruit development, and we will restrict ourselves to the mechanisms included in a time window after the floral transition and before the fertilization. Moreover, this review will not be exhaustive of the large amount of work carried on the topic, and the choices that we made to describe in large details some stories from the literature are based on the soundness of the functional work performed, and surely as well on our own preferences and expertise.First, we will give a brief overview of the Solanaceae family and some of its specificities. Then, our focus will be on the molecular mechanisms controlling floral organ identity, for which extended functional work in petunia led to substantial revisions to the famous ABC model. Finally, after reviewing some studies on floral organ initiation and growth, we will discuss floral organ maturation, using the examples of the inflated calyx of the Chinese lantern Physalis and petunia petal pigmentation.
... Gamma ray-induced flower color and shape mutations in chrysanthemum have already been reported (Datta et al., 1985;Broertjes and van Harten, 1988;Datta, 1988;Datta, 1990;Datta et al., 2001). In this study, changes in petal development during flowering may be attributed to alteration in the distribution of cell division, differentiation, and elongation (van der Krol et al., 1993;Sangeeta et al., 2019). Dilta et al. (2003) also reported a considerable reduction in the petal length of chrysanthemum plants after exposure to certain doses of gamma radiation. ...
... These proteins act as obligate heterodimers consisting of one DEF/AP3 and one GLO/PI protein, and this complex activates its own expression for maintenance of high expression levels all along petal and stamen development (Tröbner et al., 1992). In petunia, gene duplication has generated four B-class genes, namely PhDEF and PhTM6 belonging to the DEF/AP3 subfamily, and PhGLO1 and PhGLO2 belonging to the GLO/PI subfamily (Vandenbussche et al., 2004;Rijpkema et al., 2006;van der Krol et al., 1993;Angenent et al., 1992). Mutating the two members of each subfamily (phdef phtm6 or phglo1 phglo2 double mutants) produces a classical B-function mutant phenotype with homeotic transformation of petals into sepals and stamens into carpels (Vandenbussche et al., 2004;Rijpkema et al., 2006). ...
... Previously described null alleles for the PhDEF gene (also named GP or pMADS1) were obtained by either ethyl methanesulfonate (EMS) mutagenesis (de Vlaming et al., 1984;Rijpkema et al., 2006) or by -radiation (van der Krol et al., 1993). In our sequence-indexed dTph1 transposon mutant population in the W138 genetic background (Vandenbussche et al., 2008) While growing homozygous phdef-151 individuals during several seasons, we repeatedly observed the spontaneous appearance of inflorescence side branches that developed flowers with a partial restoration of petal development ( Fig. 1E-H, Fig. S1). ...
Floral homeotic MADS-box transcription factors ensure the correct development of floral organs with all their mature features, i.e. organ shape, size, colour and cellular identity. Furthermore, all plant organs develop from clonally-independent cell layers, deriving from the meristematic epidermal (L1) and internal (L2 and L3) layers. How cells from these distinct layers acquire their floral identities and coordinate their growth to ensure reproducible organ development is unclear. Here we study the development of the Petunia x hybrida (petunia) corolla, which consists of five fused petals forming a tube and pigmented limbs. We present petunia flowers expressing the B-class MADS-box gene PhDEF in the epidermis or in the mesophyll of the petal only, that we called wico and star respectively. Strikingly, the wico flowers form a very small tube while their limbs are almost normal, and the star flowers form a normal tube but very reduced and unpigmented limbs. Therefore, the star and wico phenotypes indicate that in the petunia petal, the epidermis mainly drives limb growth and pigmentation while the mesophyll mainly drives tube growth. As a first step towards the identification of candidate genes involved in specification of petal layer identities and tube/limb development, we sequenced the star and wico whole petal transcriptome at three developmental stages. Among downregulated genes in star petals, we found the major regulator of anthocyanin biosynthesis ANTHOCYANIN 1 ( AN1 ), and we showed that, in vitro , PhDEF directly binds to its terminator sequence, suggesting that it might regulate its expression. Altogether this study shows that layer-specific expression of PhDEF drives petunia tube or limb development in a highly modular fashion, which adds an extra layer of complexity to the petal development process.
... Expression of tetraspanins including tetraspanin 8 were described during the pollen development and in mature pollen in Arabidopsis thaliana (Boavida et al., 2013;Honys & Twell, 2004;Pina et al., 2005). pMADS2 was found expressed in flowers in the second whorl, however in vegetative organs were not found in Petunia (Van Der Krol et al., 1993). In Ambrosia, this gene was found to be homologous to PI that is predominantly expressed in petals and stamens, and less in carpels and sepals. ...
The highly allergenic and invasive weed Ambrosia artemisiifolia L. is a monoecius plant with separated male and female flowers. The genetic regulation of floral morphogenesis is a less understood field in the reproduction biology of this species. Therefore the objective of this work was to investigate the genetic control of sex determination during floral organogenesis. To this end, we performed a genome-wide transcriptional profiling of vegetative and generative tissues during the plant development comparing wild-growing and in vitro cultivated plants. RNA-seq on Illumina NextSeq 500 platform with an integrative bioinformatics analysis indicated differences in 80 floral gene expressions depending on photoperiodic and endogenous initial signals. Sex specificity of genes was validated based on RT-qPCR experiments. We found 11 and 16 uniquely expressed genes in female and male transcriptomes that were responsible particularly to maintain fertility and against abiotic stress. High gene expression of homologous such as FD, FT, TFL1 and CAL, SOC1, AP1 were characteristic to male and female floral meristems during organogenesis. Homologues transcripts of LFY and FLC were not found in the investigated generative and vegetative tissues. The repression of AP1 by TFL1 homolog was demonstrated in male flowers resulting exclusive expression of AP2 and PI that controlled stamen and carpel formation in the generative phase. Alterations of male and female floral meristem differentiation were demonstrated under photoperiodic and hormonal condition changes by applying in vitro treatments.
... We showed that PhTM6 acts as a B-class gene to specify stamen development redundantly with PhDEF (euAP3 gene), but is not involved in petal identity (Rijpkema et al. 2006). As a consequence, mutations in the petunia euAP3 homolog PhDEF (also called GREEN PETALS [GP]) ( Fig. 2.4c) lead to a homeotic conversion of petals into sepals, while stamen development is unaffected (van der Krol et al. 1993). Furthermore, an additional gene duplication event in the GLO/PI lineage resulted in two GLO/PI-like genes in petunia: we showed that PhGLO1 and PhGLO2 are largely redundant, except that PhGLO1 appears to have a unique function essential for the fusion of the stamen filaments to the inner petal tube and to prevent that the petal main veins become slightly sepaloid. ...
Petunia hybrida (or garden petunia) is worldwide one of the most popular bedding plants. At the same time, petunia has a decades-long history as a model species for scientific research to study a variety of processes, including floral organ development. Here we explain the genetic basis of floral organ identity in a comprehensible manner and illustrate the potential of floral organ identity mutants for ornamental plant breeding, using petunia as an example. Although the B- and C-floral organ identity functions are well conserved at the molecular level, indicating broad applicability, different species may exhibit significant differences in the degree of redundancy versus subfunctionalization/specialization among duplicated pairs of the homeotic genes. This is a direct consequence of the complex origin of different plant genomes, which were shaped by whole-genome, large and small-scale duplication events, often leading to (partial) genetic redundancy. Since classical genetic screens only can uncover nonredundant functions, this is probably the main reason why the use of floral organ identity mutants as breeding targets has remained unexplored in many ornamentals. We discuss how different breeding strategies may cope with this phenomenon.
... We showed that PhTM6 acts as a B-class gene to specify stamen development redundantly with PhDEF (euAP3 gene), but is not involved in petal identity (Rijpkema et al. 2006). As a consequence, mutations in the petunia euAP3 homolog PhDEF (also called GREEN PETALS [GP]) ( Fig. 2.4c) lead to a homeotic conversion of petals into sepals, while stamen development is unaffected (van der Krol et al. 1993). Furthermore, an additional gene duplication event in the GLO/PI lineage resulted in two GLO/PI-like genes in petunia: we showed that PhGLO1 and PhGLO2 are largely redundant, except that PhGLO1 appears to have a unique function essential for the fusion of the stamen filaments to the inner petal tube and to prevent that the petal main veins become slightly sepaloid. ...
... Normal expression of one set of the AP3–PI duplicated genes (PLAP3-2 and PLPI2) is sufficient to guarantee stamen identity, as we observed that the stamen is not affected in SCMPs, while only one of the four B-class genes (PLPI1) was normally expressed in corolla of SCMPs; thus, the corolla was transformed into calyx-like organs. Although a chromosomal deletion mutation of PhDEF (gp) in Petunia causes homeotic transformation of petals to sepallike organs only (van der Krol et al. 1993), all B-class MADS-box genes reported thus far showed a similar expression domain in floral organs (Zhang et al. 2014; Fig. 6C, D ). The specific silencing of one of these genes in the corolla only is hardly accomplished as a result of their inborn nature of autoregulation (Schwarz-Sommer et al. 1992, Zhang et al. 2014), and robust expression in both corolla and stamens (Vandenbussche et al. 2004, de Martino et al. 2006, Geuten and Irish 2010, Zhang et al. 2014). ...
Herbaceous peony (Paeonia lactiflora) is a globally important ornamental plant. Spontaneous floral mutations occur frequently during cultivation, and are selected as a way to release new cultivars, but the underlying evolutionary developmental genetics remain largely elusive. Here, we investigated a collection of spontaneous corolla mutational plants (SCMP) whose other floral organs were virtually unaffected. Unlike the corolla in normal plants (NP) that withered soon after fertilization, the transformed corolla (petals) in SCMP was greenish and persistent similar to the calyx (sepals). Epidermal cellular morphology of the SCMP corolla was also similar to that of calyx cells, further suggesting a sepaloid corolla in SCMP. Ten floral MADS-box genes from these Paeonia plants were comparatively characterized with respect to sequences and expressions. Codogenic sequence variation of these MADS-box genes was not linked to corolla changes in SCMP. However, we found that both APETALA3 (AP3)- and PISTILLATA (PI)-lineages of B-class MADS-box genes were duplicated, and subsequent selective expression alterations of these genes were closely associated with the origin of SCMP. AP3-PI obligate heterodimerization, essential for organ identity of corolla and stamens, was robustly detected. However, selective downregulation of these duplicated genes might result in a reduction of this obligate heterodimer concentration in a corolla-specific manner leading to the sepaloidy corolla in SCMP, thus representing a new sepaloidy corolla model taking advantage of gene duplication. Our work suggests that modifying floral MADS-box genes could facilitate the breeding of novel cultivars with distinct floral morphology in ornamental plants, and also provides new insights into the functional evolution of the MADS-box genes in plants.
... Mutations in either the AP3/DEF or PI/ GLO genes results in similar phenotypic variations, wherein petals are transformed into sepals, and stamens into carpels [7][8][9]. The B-class lineages apparently underwent duplications and subsequent functional divergence in some core eudicots, possibly playing a role in the diversification of floral morphology during evolution [10][11][12][13][14][15][16]. For example, in Solanaceae and Leguminosae, the PI lineage duplicated into two GLO-like genes (GLO1 and GLO2), and the AP3 lineage underwent a duplication event at the base of the core eudicots, giving rise to two AP3-like lineages called the euAP3 and paleoAP3 genes [14][15][16][17][18][19][20]. ...
... B-class MADS-box genes are not only involved in the specification of organ identity of petals and stamens, but also in the control of organ maturation. Knocking down AP3/PI at intermediate stages (stages [8][9][10] in Arabidopsis flowers induces petal-to-sepal transformations that gradually occur in consecutive buds. However, although stamens in these flowers retain their identity, they become increasingly underdeveloped and do not dehisce pollen [24]. ...
Background:
Some plants develop a breeding system that produces both chasmogamous (CH) and cleistogamous (CL) flowers. However, the underlying molecular mechanism remains elusive.
Results:
In the present study, we observed that Viola philippica develops CH flowers with short daylight, whereas an extended photoperiod induces the formation of intermediate CL and CL flowers. In response to long daylight, the respective number and size of petals and stamens was lower and smaller than those of normally developed CH flowers, and a minimum of 14-h light induced complete CL flowers that had no petals but developed two stamens of reduced fertility. The floral ABC model indicates that B-class MADS-box genes largely influence the development of the affected two-whorl floral organs; therefore, we focused on characterizing these genes in V. philippica to understand this particular developmental transition. Three such genes were isolated and respectively designated as VpTM6-1, VpTM6-2, and VpPI. These were differentially expressed during floral development (particularly in petals and stamens) and the highest level of expression was observed in CH flowers; significantly low levels were detected in intermediate CL flowers, and the lowest level in CL flowers. The observed variations in the levels of expression after floral induction and organogenesis apparently occurred in response to variations in photoperiod.
Conclusions:
Therefore, inhibition of the development of petals and stamens might be due to the downregulation of B-class MADS-box gene expression by long daylight, thereby inducing the generation of CL flowers. Our work contributes to the understanding of the adaptive evolutionary formation of dimorphic flowers in plants.
... An interesting case is at the heart of the ABC model of floral development, of which the corresponding B-class mutants ap3 (apetala3) in Arabidopsis (Jack et al., 1992) and def (deficiens) in snapdragon (Sommer et al., 1990) display homeotic conversions of petals into sepals and stamens into carpels. Remarkably, null mutants for the petunia ortholog PhDEF (also known as GREEN PETALS, GP) display only a homeotic conversion of petals into sepals, while stamen development remains unaffected (van der Krol et al., 1993; Vandenbussche et al., 2004). The molecular basis of this one whorled phenotype turned out to be caused not by a difference in the function of PhDEF itself, but by the presence of the ancestral B-class gene TM6 in petunia genome (Rijpkema et al., 2006). ...
Plant biology in general, and plant evo–devo in particular would strongly benefit from a broader range of available model systems. In recent years, technological advances have facilitated the analysis and comparison of individual gene functions in multiple species, representing now a fairly wide taxonomic range of the plant kingdom. Because genes are embedded in gene networks, studying evolution of gene function ultimately should be put in the context of studying the evolution of entire gene networks, since changes in the function of a single gene will normally go together with further changes in its network environment. For this reason, plant comparative biology/evo–devo will require the availability of a defined set of ‘super’ models occupying key taxonomic positions, in which performing gene functional analysis and testing genetic interactions ideally is as straightforward as, e.g., in Arabidopsis. Here we review why petunia has the potential to become one of these future supermodels, as a representative of the Asterid clade. We will first detail its intrinsic qualities as a model system. Next, we highlight how the revolution in sequencing technologies will now finally allows exploitation of the petunia system to its full potential, despite that petunia has already a long history as a model in plant molecular biology and genetics. We conclude with a series of arguments in favor of a more diversified multi-model approach in plant biology, and we point out where the petunia model system may further play a role, based on its biological features and molecular toolkit.
... An identical phenotype was observed in Arabidopsis ap3 or pi mutants due to the conversion of the second whorl petal into a sepal structure and the third whorl stamen into a carpel structure (Bowman et al. 1989, Jack et al. 1992, Goto and Meyerowitz 1994. The conserved functions of AP3 and PI during evolution are evidenced by the production of similar second whorl sepallike and third whorl carpel-like structures in the AP3 and PI ortholog mutants from core eudicot species (Sommer et al. 1990, Tröbner et al. 1992, Angenent et al. 1993, van der Krol et al. 1993, Yu et al. 1999, Vandenbussche et al. 2004, de Martino et al. 2006, basal eudicot species (Drea et al. 2007, Kramer et al. 2007, Lange et al. 2013) and monocot species (Ambrose et al. 2000, Nagasawa et al. 2003, Prasad and Vijayraghavan 2003, Yadav et al. 2007, Yao et al. 2008. ...
This study focused on the investigation of the effects of the PI motif and C-terminus of the Oncidium Gower Ramsey MADS box gene 8 (OMADS8), a PISTILLATA (PI) ortholog, on floral organ formation. 35S::OMADS8 completely rescued, 35S::OMADS8-PI (with the PI motif deleted) partially rescued the petal/stamen formation, whereas these deficiencies were not rescued by
35S::OMADS8-C (C-terminal 29 amino acids deleted) in pi-1 mutants. OMADS8 could interact with Arabidopsis AP3 and enter the nucleus. The nuclear entry efficiency was reduced for OMADS8-PI/AP3 and OMADS8-C/AP3. OMADS8 could also
interact with OMADS5/OMADS9 (the Oncidium AP3 ortholog) and enter the nucleus with an efficiency only slightly affected by the deletion of the C-terminal sequence
or PI motif. However, the stability of the OMADS8/OMADS5 and OMADS8/OMADS9 complexes was significantly reduced by deletion
of the C-terminal sequence or PI motif. Further analysis indicated that the expression of genes downstream of AP3/PI (BNQ1/BNQ2/GNC/At4g30270) was compensated by 35S::OMADS8 and 35S::OMADS8-PI to a level similar to wild-type plants but was not affected by 35S::OMADS8-C in the pi-1 mutants. A similar FRET efficiency was observed for Arabidopsis AG and the Oncidium AG ortholog OMADS4 for OMADS8, OMADS8-PI and OMADS8-C. These results indicated that the OMADS8 PI motif and C-terminus were
valuable for the interaction of OMADS8 with the AP3 orthologs to form higher-order heterotetrameric complexes that regulated
petal/stamen formation in both Oncidium orchids and transgenic Arabidopsis. However, the C-terminal sequence and PI motif were dispensable for the interaction of OMADS8 with the AG orthologs.
