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Modeling Sympetalous Corolla Formation (A) Initial cylindrical canvas representing primordial corolla ring at 6.5 DAI, with domains of expression used to establish growth patterns and polarity. BASE and DISTAL define regions at the proximal and distal ends of the cylinder, respectively. The proximal half of the cylinder expresses TUBE and the distal half LOBE. JUN is expressed at the petal junctions. (B) Uniform isotropic specified growth. Expression domains of TUBE, LOBE, and inter-whorl CUP (red) are shown at 10 DAI. (C) Repression of isotropic specified growth rate by CUP at petal junctions leads to formation of deep sinuses between petal primordia. (D) As in (C) except CUP expression inhibited by TUBE, leading to formation of shallow sinuses between petal primordia and a united tube. Cylinder slopes inward because of reduced circumferential growth caused by CUP. (legend continued on next page)
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Boundary domain genes, expressed within or around organ primordia, play a key role in the formation, shaping, and subdivision of planar plant organs, such as leaves. However, the role of boundary genes in formation of more elaborate 3D structures, which also derive from organ primordia, remains unclear. Here we analyze the role of the boundary doma...
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... this framework, tissue is treated as a connected continuous material, termed the canvas. We used a shallow cylinder to represent the corolla meristematic ring around the floral meristem at 6.5 DAI and subdivided it into four domains along the proximodistal axis: BASE, TUBE, LOBE, and DISTAL ( Figure 4A). We also subdivided each petal primordium along its mediolateral axis with JUN, which is ex- pressed at the lateral edges or junctions of each primordium. ...
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... first considered the effects of isotropic specified growth in the plane of the canvas. If areal specified growth rate was uni- form (Figure 4B, 6.5 DAI), the cylindrical canvas simply became enlarged ( Figure 4B, 10 DAI). Inter-whorl CUP expression was indicated at the corolla base (shown in red, Figure 4B, 10 DAI). ...
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... areal specified growth rate was uni- form (Figure 4B, 6.5 DAI), the cylindrical canvas simply became enlarged ( Figure 4B, 10 DAI). Inter-whorl CUP expression was indicated at the corolla base (shown in red, Figure 4B, 10 DAI). To account for the development of separate petals, we intro- duced repression of growth at the petal junctions, mediated by the action of CUP ( Figure 4C, 6.5 DAI). ...
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... CUP expression was indicated at the corolla base (shown in red, Figure 4B, 10 DAI). To account for the development of separate petals, we intro- duced repression of growth at the petal junctions, mediated by the action of CUP ( Figure 4C, 6.5 DAI). Running this model led to formation of divisions at the petal junctions ( Figure 4C, 10 DAI). ...
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... account for the development of separate petals, we intro- duced repression of growth at the petal junctions, mediated by the action of CUP ( Figure 4C, 6.5 DAI). Running this model led to formation of divisions at the petal junctions ( Figure 4C, 10 DAI). The depth of the divisions was reduced if junctional CUP was repressed in the tube region, corresponding to a gap in the CUP junctional domain ( Figure 4D, 6.5 DAI). ...
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... this model led to formation of divisions at the petal junctions ( Figure 4C, 10 DAI). The depth of the divisions was reduced if junctional CUP was repressed in the tube region, corresponding to a gap in the CUP junctional domain ( Figure 4D, 6.5 DAI). This led to the formation of an inwardly sloping corolla tube with sinuses between the lobes ( Figure 4D, 10 DAI). ...
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... depth of the divisions was reduced if junctional CUP was repressed in the tube region, corresponding to a gap in the CUP junctional domain ( Figure 4D, 6.5 DAI). This led to the formation of an inwardly sloping corolla tube with sinuses between the lobes ( Figure 4D, 10 DAI). The inward sloping (a passive effect of growth repression) could be reduced by inhib- iting growth of the canvas by BASE ( Figure 4E). ...
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... led to the formation of an inwardly sloping corolla tube with sinuses between the lobes ( Figure 4D, 10 DAI). The inward sloping (a passive effect of growth repression) could be reduced by inhib- iting growth of the canvas by BASE ( Figure 4E). Thus, if CUP acts by repressing growth, the generation of a sympetalous flower may reflect inhibition of CUP in a petal junction zone, allowing the non-expressing region to grow and form the tube. ...
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... analysis indicates that early petal growth is anisotropic, being higher parallel to the proximodistal axis than perpendicular to it [16]. To determine how this feature influences shape, we intro- duced a polarity field, with specified growth rate higher parallel to the polarity ( Figure 4F, 6.5 DAI). Running this model gave a taller and narrower cylinder than for the isotropic model ( Figure 4F Figure 4I). ...
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... determine how this feature influences shape, we intro- duced a polarity field, with specified growth rate higher parallel to the polarity ( Figure 4F, 6.5 DAI). Running this model gave a taller and narrower cylinder than for the isotropic model ( Figure 4F Figure 4I). This shape resembled the starting shape used for modeling corolla morpho- genesis (compare Figure 4I with Figure 5I, see also [16]). ...
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... determine how this feature influences shape, we intro- duced a polarity field, with specified growth rate higher parallel to the polarity ( Figure 4F, 6.5 DAI). Running this model gave a taller and narrower cylinder than for the isotropic model ( Figure 4F Figure 4I). This shape resembled the starting shape used for modeling corolla morpho- genesis (compare Figure 4I with Figure 5I, see also [16]). ...
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... this model gave a taller and narrower cylinder than for the isotropic model ( Figure 4F Figure 4I). This shape resembled the starting shape used for modeling corolla morpho- genesis (compare Figure 4I with Figure 5I, see also [16]). Although specified growth was only repressed in inter-whorl domains in these models, the deformation of tissue extended to nearby re- gions, illustrated by the deformation of an initially square grid near the sinus (magnified region in Figure 4I). ...
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... shape resembled the starting shape used for modeling corolla morpho- genesis (compare Figure 4I with Figure 5I, see also [16]). Although specified growth was only repressed in inter-whorl domains in these models, the deformation of tissue extended to nearby re- gions, illustrated by the deformation of an initially square grid near the sinus (magnified region in Figure 4I). The grid becomes curved and shows modified growth outside the CUP domain. ...
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... possibility is that sinus formation depends on not only growth repression at boundaries, but also growth promotion within the body of the pri- mordium. To model this hypothesis, specified growth parallel to the polarity was promoted in and around the midline of each petal primordium, using a mediolateral factor MED ( Figure 4J). Inward sloping of the corolla was also reduced by inhibiting growth by BASE as in previous models. ...
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... sloping of the corolla was also reduced by inhibiting growth by BASE as in previous models. Running this model gave five primordia separated by shallow sinuses ( Figure 4K). Expression of CUP throughout the petal junction, led to further sharpening and deepening of the sinuses ( Figure 4L). ...
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... this model gave five primordia separated by shallow sinuses ( Figure 4K). Expression of CUP throughout the petal junction, led to further sharpening and deepening of the sinuses ( Figure 4L). Repression of CUP in the tube region, gave a sympetalous corolla with five lobes (Fig- ure 4M). ...
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... of CUP throughout the petal junction, led to further sharpening and deepening of the sinuses ( Figure 4L). Repression of CUP in the tube region, gave a sympetalous corolla with five lobes (Fig- ure 4M). If CUP was maintained in only three junctions, by making its expression depend on factor RIGHT ( Figure 4N), an asymmetric corolla was generated with a lip region at sinuses where CUP was lacking (blue arrow). ...
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... of CUP in the tube region, gave a sympetalous corolla with five lobes (Fig- ure 4M). If CUP was maintained in only three junctions, by making its expression depend on factor RIGHT ( Figure 4N), an asymmetric corolla was generated with a lip region at sinuses where CUP was lacking (blue arrow). Thus, shaping and growth around sinuses may reflect a combination of growth repression at different bound- aries and promotion within primordia. ...
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... initial canvas corresponds to 10 DAI and comprises a cylinder with five lobes mediolateral [15,16]. CUP expression at early stages would contribute to shaping the early sympetalous corolla (illustrated in models of Figure 4), which is taken as a starting shape for the previously published model. This would be achieved by CUP expression at petal junctions being activated by mediolat- eral factors, which would act in combination with CUP to inhibit growth. ...
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... and signaling factors can be specified throughout the canvas. The distribution of factors is shown in Figures 4A and 4J. A growth regulatory network (KRN) controls the specified growth parallel (K par ) and perpendicular (K per ) to the local polarity, established by taking the gradient of a diffusible factor POLARIZER (POL). ...
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... growth regulatory network (KRN) controls the specified growth parallel (K par ) and perpendicular (K per ) to the local polarity, established by taking the gradient of a diffusible factor POLARIZER (POL). For anisotropic growth models, the polarity field is established by producing POL at the bottom of the canvas (through factor BASE) and fixing it to a low concentration at the top (through factor DISTAL). Figure 4N: CUP expression at a subset of junctions As for Figure 4M except that i jcup expression depends on factor RIGHT. ...
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... growth regulatory network (KRN) controls the specified growth parallel (K par ) and perpendicular (K per ) to the local polarity, established by taking the gradient of a diffusible factor POLARIZER (POL). For anisotropic growth models, the polarity field is established by producing POL at the bottom of the canvas (through factor BASE) and fixing it to a low concentration at the top (through factor DISTAL). Figure 4N: CUP expression at a subset of junctions As for Figure 4M except that i jcup expression depends on factor RIGHT. ...
Citations
... Although morphogenesis is a fascinating subject of plant research for over 100 years (Thompson, 1917), the interest of plant researchers in the formation of shapes has increased significantly in recent years. Regardless of whether the shapes of organs, ranging from ovules (Vijayan et al., 2021) to leaves (Bhatia et al., 2021;Kierzkowski et al., 2019;Zhao et al., 2020) and flowers (Rebocho et al., 2017), or isolated tissues such as leaf pavement cells and the shoot apical meristem (Hamant et al., 2008;Sampathkumar et al., 2019) or even unicellular models such as trichomes and root hairs are the matter of study, dynamic recording and quantification of growth processes are applied in almost all areas, which has given new impetus to the field of morphodynamics. In this context, the abundance of data and the ease of recording (by today) are rapidly saturating existing methods for describing and quantifying shapes. ...
All plant cells are encased by walls, which provide structural support and control their morphology. How plant cells regulate the deposition of the wall to generate complex shapes is a topic of ongoing research. Scientists have identified several model systems, the epidermal pavement cells of cotyledons and leaves being an ideal platform to study the formation of complex cell shapes. These cells indeed grow alternating protrusions and indentations resulting in jigsaw puzzle cell shapes. How and why these cells adopt such shapes has shown to be a challenging problem to solve, notably because it involves the integration of molecular and mechanical regulation together with cytoskeletal dynamics and cell wall modifications. In this review, we highlight some recent progress focusing on how these processes may be integrated at the cellular level along with recent quantitative morphometric approaches.
... Research combining genetics and computational simulation indicates that the cupshaped traps of the carnivorous plant Utricularia gibba are a result of restricted adaxial leaf side development [153,154]. Similarly, the ornate dragon snout-shaped flower of Antirrhinum is produced via petal separation led by altered expression of a boundary gene [155]. ...
The manner by which plant organs gain their shape is a longstanding question in developmental biology. Leaves, as typical lateral organs, are initiated from the shoot apical meristem that harbors stem cells. Leaf morphogenesis is accompanied by cell proliferation and specification to form the specific 3D shapes, with flattened lamina being the most common. Here, we briefly review the mechanisms controlling leaf initiation and morphogenesis, from periodic initiation in the shoot apex to the formation of conserved thin-blade and divergent leaf shapes. We introduce both regulatory gene patterning and biomechanical regulation involved in leaf morphogenesis. How phenotype is determined by genotype remains largely unanswered. Together, these new insights into leaf morphogenesis resolve molecular chains of events to better aid our understanding.
... The Petunia nam mutants lack a shoot apical meristem and show defects in organ boundaries [4]. This same phenotype characterizes the Arabidopsis cuc1 and cuc2 mutants and the cupuliformis (cup) mutant of the snapdragon, A. majus [2,8,15]. ...
... Most studies into NAC transcription factors analyzed their function in root and leaf development and organ boundary formation [6][7][8][22][23][24][25]. However, in A. majus, the role of some NACs in the formation of the lip, the peculiar ventral petal of the snapdragon flower, was also explored. [15]. In this species, the cup mutant displays defects in the vegetative tissues, such as the cuc and nam mutants; it also shows an altered flower development. ...
... In particular, its corolla has an open mouth that lacks the folding characteristic of the palate and the lip regions. These mutant flowers lose bilateral symmetry, have similar petals, and their stamens are fused with the corolla tube [15,26]. CUP is a NAC transcription factor, and its involvement in flower formation was also described for Arabidopsis and Petunia [8,15,24]. ...
Plant transcription factors are involved in different developmental pathways. NAC transcription factors (No Apical Meristem, Arabidopsis thaliana Activating Factor, Cup-shaped Cotyledon) act in various processes, e.g., plant organ formation, response to stress, and defense mechanisms. In Antirrhinum majus, the NAC transcription factor CUPULIFORMIS (CUP) plays a role in determining organ boundaries and lip formation, and the CUP homologs of Arabidopsis and Petunia are involved in flower organ formation. Orchidaceae is one of the most species-rich families of angiosperms, known for its extraordinary diversification of flower morphology. We conducted a transcriptome and genome-wide analysis of orchid NACs, focusing on the No Apical Meristem (NAM) subfamily and CUP genes. To check whether the CUP homologs could be involved in the perianth formation of orchids, we performed an expression analysis on the flower organs of the orchid Phalaenopsis aphrodite at different developmental stages. The expression patterns of the CUP genes of P. aphrodite suggest their possible role in flower development and symmetry establishment. In addition, as observed in other species, the orchid CUP1 and CUP2 genes seem to be regulated by the microRNA, miR164. Our results represent a preliminary study of NAC transcription factors in orchids to understand the role of these genes during orchid flower formation.
... For example, when they differentiate in a tissue that is about to cease its expansion (such as the tip of the leaf or the anther), a stomata's fast growth may not be fully compensated for by the prolonged expansion of adjacent epidermal cells. In this case, differential growth between connected cells can generate mechanical conflicts that are able to alter rates and orientations of cellular growth (Echevin et al., 2019;Rebocho et al., 2017). The neighboring cells must physically accommodate this opposing behavior by either changing their geometry or specified growth rates to ensure reproducible development. ...
Coordination of growth, patterning and differentiation is required for shaping organs in multicellular organisms. In plants, cell growth is controlled by positional information, yet the behavior of individual cells is often highly heterogeneous. The origin of this variability is still unclear. Using time-lapse imaging, we determined the source and relevance of cellular growth variability in developing organs of Arabidopsis thaliana. We show that growth is more heterogeneous in the leaf blade than in the midrib and petiole, correlating with higher local differences in growth rates between neighboring cells in the blade. This local growth variability coincides with developing stomata. Stomatal lineages follow a specific, time-dependent growth program that is different from that of their surroundings. Quantification of cellular dynamics in the leaves of a mutant lacking stomata, as well as analysis of floral organs, supports the idea that growth variability is mainly driven by stomata differentiation. Thus, the cell-autonomous behavior of specialized cells is the main source of local growth variability in otherwise homogeneously growing tissue. Those growth differences are buffered by the immediate neighbors of stomata and trichomes to achieve robust organ shapes.
... It appears that ABCE-class and CYC2-like genes in Asteraceae are not the hub genes in the regulatory network of disc and ray f loret differentiation. WGCNA showed that the hub genes regulating disc and ray floret differentiation in the capitulum were NAM and LOB30, and NAM/CUC and LOB30 subfamily genes not only regulate the initiation and orientation of organ primordia in early f lower development but also respond to inf lorescence meristem-related genes and floral identity genes [29][30][31]. Based on the hub roles of NAM and LOB30 in stages 5 and 6, we concluded that the two genes might regulate the differentiation of disc and ray f loret primordia in early capitulum development and that they could interact with downstream genes to regulate the f loral organ identity and development of each f loret on the capitulum. Duplication of NAM and its chromosome position in the C. lavandulifolium genome indicated that NAM might be a special key gene in regulating the diverse capitula types of chrysanthemum. ...
... Duplication of NAM and its chromosome position in the C. lavandulifolium genome indicated that NAM might be a special key gene in regulating the diverse capitula types of chrysanthemum. Protein interactions showed that these hub genes could interact with LFY, which has been proven to regulate ray floret development in Gerbera [31]. Previous studies supported the idea that the capitulum was derived from a cyme in which peripheral branches were inhibited [32]. ...
Cultivated chrysanthemum (Chrysanthemum × morifolium Ramat.) is a beloved ornamental crop due to the diverse capitula types among varieties, but the molecular mechanism of capitulum development remains unclear. Here, we report a 2.60 Gb chromosome-scale reference genome of C. lavandulifolium, a wild Chrysanthemum species found in China, Korea and Japan. The evolutionary analysis of the genome revealed that only recent tandem duplications occurred in the C. lavandulifolium genome after the shared whole genome triplication (WGT) in Asteraceae. Based on the transcriptomic profiling of six important developmental stages of the radiate capitulum in C. lavandulifolium, we found genes in the MADS-box, TCP, NAC and LOB gene families that were involved in disc and ray floret primordia differentiation. Notably, NAM and LOB30 homologs were specifically expressed in the radiate capitulum, suggesting their pivotal roles in the genetic network of disc and ray floret primordia differentiation in chrysanthemum. The present study not only provides a high-quality reference genome of chrysanthemum but also provides insight into the molecular mechanism underlying the diverse capitulum types in chrysanthemum.
... For Fig. S6, our results suggest that A-, B-, and C-class genes are involved in the petaloid formation, which is in agreement with previous studies. Deficiencies in inter-whorl boundaries can result in hybrid structures such as petal-stamens (Rebocho et al., 2017). The stamen petaloidy and carpel petaloidy in lotus may also be caused by defects in inter-whorl boundaries. ...
Lotus ( Nelumbo nucifera ) is a highly recognized flower with high ornamental value. Flower color and flower morphology are two main factors for flower lotus breeding. Petaloidy is a universal phenomenon in lotus flowers. However, the genetic regulation of floral organ petaloidy in lotus remains elusive. In this study, the transcriptomic analysis was performed among three organs, including petal, carpel petaloidy, and carpel in lotus. A total of 1,568 DEGs related to carpel petaloidy were identified. Our study identified one floral homeotic gene encoded by the MADS-box transcription factor, AGAMOUS ( AG ) as the candidate gene for petaloid in lotus. Meanwhile, a predicted labile boundary in floral organs of N. nucifera was hypothesized. In summary, our results explored the candidate genes related to carpel petaloidy, setting a theoretical basis for the molecular regulation of petaloid phenotype.
... According to the previous studies , 2015a, 2015bMartini et al., 2015;Ortiz-Miranda et al., 2016a,b), different degrees of variability can be observed within different plant species. The chemical compounds present in plant tissue are mainly controlled by genetic factors (Nakatsuka et al., 2008;Nishihara and Nakatsuka, 2011;Rebocho et al., 2017). Therefore, the electrochemical fingerprint recorded for plants certainly reflects the genetic diversities between species. ...
A quick and low-cost method for traditional medical herbs identification is essential for the plant resources and pharmaceutical industries. The electrochemical voltammetric profile of plant tissues can be considered as a unique fingerprint available for herbal traditional medical herbs identification. In this work, a chip-based portable method is proposed for measuring the electrochemical fingerprint of a series of medicinal herbs with the assistance of graphene. Fingerprints were converted into patterns, colors and pixels for easy identification. The results indicated that the proposed electrochemical fingerprint sensor can recognize medicinal herbs in fresh, dried and prepared forms. In addition, the taxonomic relationships of these species were studied based on the recorded fingerprints, since the degree of differences in electroactive compounds can reflect genetic differences. The results indicate that the electrochemical fingerprints recorded from fresh samples can effectively reflect the phylogenetic position of species.
... During the development, there are multiple possibilities to modulate these processes in terms of both space and time to generate diverse shapes Whitewoods et al., 2020). Furthermore, distinct developmental patterns can produce comparable geometries (Green et al., 1970;Coen et al., 2004;Rebocho et al., 2017;Solly et al., 2017). Therefore, it is impossible to understand organ development solely by observing their final shape. ...
Development of multicellular organisms is a complex process involving precise coordination of growth among individual cells. Understanding organogenesis requires measurements of cellular behaviors over space and time. In plants, such a quantitative approach has been successfully used to dissect organ development in both leaves and external floral organs such as sepals. However, the observation of floral reproductive organs is hampered as they develop inside tightly closed floral buds, and are therefore difficult to access for imaging. We developed a confocal time-lapse imaging method, applied here to Arabidopsis (Arabidopsis thaliana), that allows full quantitative characterization of the development of stamens, the male reproductive organs. Our lineage tracing reveals the early specification of the filament and the anther. Formation of the anther lobes is associated with a temporal increase of growth at the lobe surface that correlates with intensive growth of the developing locule. Filament development is very dynamic and passes through three distinct phases: (1) initial intense, anisotropic growth and high cell proliferation; (2) restriction of growth and proliferation to the filament proximal region; (3) resumption of intense and anisotropic growth, displaced to the distal portion of the filament, without cell proliferation. This quantitative atlas of cellular growth dynamics provides a solid framework for future studies into stamen development.
... Notably, the floral organ-specific qRT-PCRs for HcPTL showed a pattern of expression more consistent with data from A. thaliana, namely, a higher expression in sepals and petals at late developmental stages (See Fig. S3). This divergence in function of a boundary gene with respect to its documented role in A. thaliana floral development, where HcPTL seems to promote growth in floral organs rather than limiting it, was documented in another boundary gene related with the CUC1-3 genes, CUPULIFORMIS (CUP) in the Antirrhinum flower (Rebocho et al. 2017). In this context, it might be possible that the slight growth rate difference observed between petal and stamen/inner androecium members in H. coronarium (Fig. 6e-h) might be explained, at least in part, by the differential expression of HcPTL in the dorsal/ventral part of the common primordia, so as to ensure that the petals envelop the stamen/inner androecium. ...
The flower of Hedychium coronarium possesses highly specialized floral organs: a synsepalous calyx, petaloid staminodes and a labellum. The formation of these organs is controlled by two gene categories: floral organ identity genes and organ boundary genes, which may function individually or jointly during flower development. Although the floral organogenesis of H. coronarium has been studied at the morphological level, the underlying molecular mechanisms involved in particular organ morphologies that emerge in flower development still remain poorly understood. Here, we used comparative transcriptomics combined with Real-time quantitative PCR to investigate gene expression patterns of ABC-class genes in H. coronarium flowers, as well as the homolog of PETAL LOSS (HcPTL). Our studies found that stamen/petal identity or stamen fertility in H. coronarium was not necessarily correlated with the differential expression of HcAP3 and HcAG. We also found a novel spatio-temporal expression pattern for HcPTL mRNA, suggesting it may have evolved a lineage-specific role in the morphogenesis of the Hedychium flower. Our study provides a new transcriptome reference and a functional hypothesis regarding the role of a boundary gene in organ fusion that should be further addressed through phylogenetic analyzes of this gene, as well as functional studies.
... As in the development of vegetative phyllotaxis, floral organs are initiated around a floral meristem, although there are many exceptions depending on species and/or developmental stages. Some specialized organ initiations are observed, such as the ring meristem, for example in Ranunculales (Becker 2016), a common primordium that further develops into multiple organ primordia, such as in Fabaceae (Tucker 2003), and early and late fusion of primordia, such as in Antirrhinum majus L. (Rebocho et al. 2017). ...
Floral phyllotaxis is a relatively robust phenotype; trimerous and pentamerous arrangements are widely observed in monocots and core eudicots. Conversely, it also shows variability in some angiosperm clades such as ‘ANA’ grade (Amborellales, Nymphaeales, and Austrobaileyales), magnoliids, and Ranunculales. Regardless of the phylogenetic relationship, however, phyllotactic pattern formation appears to be a common process. What are the causes of the variability in floral phyllotaxis and how has the variation of floral phyllotaxis contributed to floral diversity? In this review, I summarize recent progress in studies on two related fields to develop answers to these questions. First, it is known that molecular and cellular stochasticity are inevitably found in biological systems, including plant development. Organisms deal with molecular stochasticity in several ways, such as dampening noise through gene networks or maintaining function through cellular redundancy. Recent studies on molecular and cellular stochasticity suggest that stochasticity is not always detrimental to plants and that it is also essential in development. Second, studies on vegetative and inflorescence phyllotaxis have shown that plants often exhibit variability and flexibility in phenotypes. Three types of phyllotaxis variations are observed, namely, fluctuation around the mean, transition between regular patterns, and a transient irregular organ arrangement called permutation. Computer models have demonstrated that stochasticity in the phyllotactic pattern formation plays a role in pattern transitions and irregularities. Variations are also found in the number and positioning of floral organs, although it is not known whether such variations provide any functional advantages. Two ways of diversification may be involved in angiosperm floral evolution: precise regulation of organ position and identity that leads to further specialization of organs and organ redundancy that leads to flexibility in floral phyllotaxis.
