Ventral Petals Research Articles

Morphological characterization and screening of Impatiens wild species for heat tolerance

Impatiens sp. is an annual plant that flowers all year round. High temperature stress is a major challenge limiting crop productivity. The research was conducted at experiment garden in Palasari Cipanas, BRIN, Indonesia, at an altitude of 1000 ASL, from January - April 2023. The aim of the research was to explore the morphological variation of Impatiens wild species and to obtain some heat tolerance accession for next breeding program. Twenty nine accession of Impatiens were observed for the qualitative and quantitative data including the evaluation of heat tolerance. Twelve qualitative characters were recorded. The qualitative characters were analyzed as degree of similarity. DICE Similarity coefficient of qualitative data was 0.06. Broad variability in the genotypic, phenotypic variances and genetic advance was found for leaf length, leaf width and heat tolerance score. Of the electrolyte leakage analyses, it was found that flower length, ventral petal length width, lateral petal length and spur length positively support the high tolerance of Impatiens accession to heat stress. The darker color of the stem, anther, and bract is followed by a reduction in the dimension of flower width, lateral petal width, dorsal petal width and spur length but the increased leaf thicknesses. There was no direct correlation between the heat tolerance score and the leaf thickness. The largest data diversity explained by 3 factors with a total variance of 68.88 %.

Genetic control of the lateral petal shape and identity of asymmetric flowers in mungbean (Vigna radiata L.).

Broad diversity of flowers in Fabaceae provides a good system to investigate development and evolution of floral symmetry in higher plants. Many studies have demonstrated a conserved mechanism controlling development of zygomorphic flower during last decades. However, the molecular basis of how asymmetric flower established is largely unknown. In this study, we characterized mutants named keeled wings (kw) in mungbean (Vigna radiata L.), which is a legume species with asymmetric flowers. Compared to those in the wild type plants, the lateral petals were ventralized in the kw mutants. Map-based cloning showed that KW was VrCYC3 gene in mungbean, the ortholog of Lotus japonicus CYC3 (LjCYC3) and Pisum sativum CYC3 (PsCYC3). In addition, another two CYC-like genes named VrCYC1 and VrCYC2 were identified from mungbean genome. The three CYC-like genes displayed distinct expression patterns in dorsal, lateral and ventral petals. It was found that VrCYC3 was located in nucleus. Further analysis showed that VrCYC3 had transcription activity and could interact with VrCYC1 and VrCYC2 in yeast cell. Moreover, the deletion of two amino acid residues in the R domain of VrCYC3 protein could decrease its interaction with VrCYC1 and VrCYC2 proteins. Our results suggest that LjCYC3/VrCYC3 orthologs play conserved roles determining the lateral petal shape and identity of zygomorphic flower as well as asymmetric flower in Papilionoideae.

Transcriptomic Analysis Suggests Auxin Regulation in Dorsal-Ventral Petal Asymmetry of Wild Progenitor Sinningia speciosa.

The establishment of dorsal–ventral (DV) petal asymmetry is accompanied by differential growth of DV petal size, shape, and color differences, which enhance ornamental values. Genes involved in flower symmetry in Sinningia speciosa have been identified as CYCLOIDEA (SsCYC), but which gene regulatory network (GRN) is associated with SsCYC to establish DV petal asymmetry is still unknown. To uncover the GRN of DV petal asymmetry, we identified 630 DV differentially expressed genes (DV-DEGs) from the RNA-Seq of dorsal and ventral petals in the wild progenitor, S. speciosa ‘ES’. Validated by qRT-PCR, genes in the auxin signaling transduction pathway, SsCYC, and a major regulator of anthocyanin biosynthesis were upregulated in dorsal petals. These genes correlated with a higher endogenous auxin level in dorsal petals, with longer tube length growth through cell expansion and a purple dorsal color. Over-expression of SsCYC in Nicotiana reduced petal size by regulating cell growth, suggesting that SsCYC also controls cell expansion. This suggests that auxin and SsCYC both regulate DV petal asymmetry. Transiently over-expressed SsCYC, however, could not activate most major auxin signaling genes, suggesting that SsCYC may not trigger auxin regulation. Whether auxin can activate SsCYC or whether they act independently to regulate DV petal asymmetry remains to be explored in the future.

Duplication and expression patterns of CYCLOIDEA-like genes in Campanulaceae

BackgroundCYCLOIDEA (CYC)-like transcription factors pattern floral symmetry in most angiosperms. In core eudicots, two duplications led to three clades of CYC-like genes: CYC1, CYC2, and CYC3, with orthologs of the CYC2 clade restricting expression dorsally in bilaterally symmetrical flowers. Limited data from CYC3 suggest that they also play a role in flower symmetry in some asterids. We examine the evolution of these genes in Campanulaceae, a group that contains broad transitions between radial and bilateral floral symmetry and 180° resupination (turning upside-down by twisting pedicle).ResultsWe identify here all three paralogous CYC-like clades across Campanulaceae. Similar to other core eudicots, we show that CamCYC2 duplicated near the time of the divergence of the bilaterally symmetrical and resupinate Lobelioideae. However, in non-resupinate, bilaterally symmetrical Cyphioideae, CamCYC2 appears to have been lost and CamCYC3 duplicated, suggesting a novel genetic basis for bilateral symmetry in Cyphioideae. We additionally, utilized qRT-PCR to examine the correlation between CYC-like gene expression and shifts in flower morphology in four species of Lobelioideae. As expected, CamCYC2 gene expression was dorsoventrally restricted in bilateral symmetrical flowers. However, because Lobelioideae have resupinate flowers, both CamCYC2A and CamCYC2B are highly expressed in the finally positioned ventral petal lobes, corresponding to the adaxial side of the flower relative to meristem orientation.ConclusionsOur sequences across Campanulaceae of all three of these paralogous groups suggests that radially symmetrical Campanuloideae duplicated CYC1, Lobelioideae duplicated CYC2 and lost CYC3 early in their divergence, and that Cyphioideae lost CYC2 and duplicated CYC3. This suggests a dynamic pattern of duplication and loss of major floral patterning genes in this group and highlights the first case of a loss of CYC2 in a bilaterally symmetrical group. We illustrate here that CYC expression is conserved along the dorsoventral axis of the flower even as it turns upside-down, suggesting that at least late CYC expression is not regulated by extrinsic factors such as gravity. We additionally show that while the pattern of dorsoventral expression of each paralog remains the same, CamCYC2A is more dominant in species with shorter relative finally positioned dorsal lobes, and CamCYC2B is more dominant in species with long dorsal lobes.

Quantification of petal patterns and colours of genus Sinningia (GESNERIACEAE)

Plants belonging to genus Sinningia are popular ornamental plants with diverse petal patterns and fascinating petal colours. The patterns and colours of petals are crucial horticultural properties that determine a plant's commercial value. Generally, the patterns and colours of petals are evaluated by experienced horticulturalists. However, manual evaluation can be subjective and the decision criterion could fluctuate due to fatigue. This work proposed a method to automatically quantify the petal patterns and colours by investigating 11 species of Sinningia . The images of the ventral petal of flower specimens were captured using flatbed scanners. The regions of interest (ROI) were defined and segmented from ventral images. Subsequently, a fully convolutional network was applied to the ROI for automatically segmenting variegated parts (i.e., spots, strips, and plaques) from the background. The patterns and colours of petals were then analysed. The proposed method can be used for the automation of petal pattern rating, which generally is performed using naked-eye observations. • A method was proposed to quantify petal colours and patterns. • A fully convolutional network (FCN) was trained to segment patterns of petals. • The patterns were categorised into 3 categories: spots, strips, and plaques. • The method is tested on the ventral petals of 10 species of genus Sinningia. • This approach is objective and precise compared with the method in DUS test.

CmBES1 is a regulator of boundary formation in chrysanthemum ray florets

Chrysanthemum (Chrysanthemum morifolium) is an ideal model species for studying petal morphogenesis because of the diversity in the flower form across varieties; however, the molecular mechanisms underlying petal development are poorly understood. Here, we show that the brassinosteroid transcription factor BRI1-EMS-SUPPRESSOR 1 (CmBES1) in chrysanthemum (C. morifolium cv. Jinba) is important for organ boundary formation because it represses organ boundary identity genes. Chrysanthemum plants overexpressing CmBES1 displayed increased fusion of the outermost ray florets due to the loss of differentiation of the two dorsal petals, which developed simultaneously with the ventral petals. RNA-seq analysis of the overexpression lines revealed potential genes and pathways involved in petal development, such as CUP-SHAPED COTYLEDON (CUC2), CYCLOIDEA 4 (CYC4), genes encoding MADS-box transcription factors and homeodomain-leucine zippers (HD-Zips) and auxin pathway-related genes. This study characterizes the role of CmBES1 in ray floret development by its modulation of flower development and boundary identity genes in chrysanthemum.

Floral ontogeny and molecular evaluation of anthocyanin biosynthesis pathway in pinwheel phenotype of Saintpaulia inontha Wendl. periclinal chimera

The color of African violet flowers (Saintpaulia ionantha Wendl.) is derived from anthocyanin pigments. A mutation in the L1 layer of the SAM suppresses the anthocyanin biosynthesis pathway and eventually generates a pinwheel phenotype of periclinal chimera (cells of different genotypes). The aim of the present research was to understand the coloration pathway of petals and how color changes with phenotype. Flower development was investigated by light and scanning electron microscopy (SEM). Expression of nine genes involved in anthocyanin biosynthesis pathway in monochromatic and pinwheel phenotypes were evaluated by Real-Time PCR. Anthocyanin present in pinwheel petals was analyzed by HPLC. Microscopic studies revealed that the ventral petals were formed before the dorsal petals and that the petal primordia separated in the early stages of floral development. Saintpaulia flower is protandry and the tapetum layer is of the secretory type. The ovules are anatropous and are within the superior ovary with lateral placentation. Gene expression analysis showed that CHS and CHI genes were expressed at all stages of floral development, but hydroxylase genes increased during intermediate stages. Biosynthetic genes were highly expressed in the purple sections of the pinwheel petals, whereas the expression of F3H gene was significantly lower in the white section. The WDR transcription factor appears to have no association with the anthocyanin biosynthesis pathway genes in the white section. HPLC analysis showed that when F3H gene expression was reduced in the white part of the petals, the product of this gene (dihydrokaempferol component) did not accumulate. Color change is one of the most effective methods to create new cultivars. Details of floral pigment biosynthesis pathway and the production of new cultivars can respond to consumer demand and market preservation.

Genetic insights into the modification of the pre-fertilization mechanisms during plant domestication.

Plant domestication is the process of adapting plants to human use by selecting specific traits. The selection process often involves the modification of some components of the plant reproductive mechanisms. Allelic variants of genes associated with flowering time, vernalization, and the circadian clock are responsible for the adaptation of crops, such as rice, maize, barley, wheat, and tomato, to non-native latitudes. Modifications in the plant architecture and branching have been selected for higher yields and easier harvests. These phenotypes are often produced by alterations in the regulation of the transition of shoot apical meristems to inflorescences, and then to floral meristems. Floral homeotic mutants are responsible for popular double-flower phenotypes in Japanese cherries, roses, camellias, and lilies. The rise of peloric flowers in ornamentals such as snapdragon and florists' gloxinia is associated with non-functional alleles that control the relative expansion of lateral and ventral petals. Mechanisms to force outcrossing such as self-incompatibility have been removed in some tree crops cultivars such as almonds and peaches. In this review, we revisit some of these important concepts from the plant domestication perspective, focusing on four topics related to the pre-fertilization mechanisms: flowering time, inflorescence architecture, flower development, and pre-fertilization self-incompatibility mechanisms.

BIGGER ORGANS and ELEPHANT EAR-LIKE LEAF1 control organ size and floral organ internal asymmetry in pea.

Control of organ size and shape by cell proliferation and cell expansion is a fundamental process during plant development, but the molecular mechanisms that set the final size and shape of determinate organs in plants remain unclear, especially in legumes. In this study, we characterized several mutants including bigger organs (bio) and elephant-ear-like leaf 1 (ele1) in pea that displayed similar phenotypes, with enlarged leaves and symmetrical lateral and ventral petals. Genetic analysis showed that BIO interacted with the specific regulators SYMMETRICAL PETAL1 (SYP1) and SYP5 to control floral organ internal asymmetry in pea. Using a comparative approach, we cloned BIO and ELE1, revealing that they encode a KIX domain protein and an ortholog of Arabidopsis PEAPOD (PPD), respectively. Furthermore, genetic analysis, physical interaction assays, and gene expression analysis showed that BIO and ELE1 physically interact with each other and with the transcription factor LATHYROIDES (LATH) to repress expression of downstream genes such as GROWTH-REGULATING-FACTOR 5. Our data show that the BIO-ELE1 module in legumes plays a key role in regulating organ development to create distinct final forms with characteristic size and shape.

Quantifying colour and spot characteristics for the ventral petals in Sinningia speciosa

This study examined the colour and spot patterns for the ventral petals of a cross line in Sinningia speciosa. The second-generation individuals of the cross line exhibited phenotypic segregation in floral colour and spot patterns. Three colour traits (colour region ratio, region of interest colour, and colour gradient) and five spot traits (spot quantity, spot density, spot area ratio, spot colour, and background colour) were defined and quantified using image processing techniques. The variation in the traits and the correlations between the traits were also investigated. The results indicated a considerable degree of variation among the traits. The proposed approach can quantify petal traits more objectively and precisely compared with conventional naked eye examination. Thus, it can be used for applications, such as new flower variety determination, that require precise trait quantification.

High-Throughput RNA-Seq Data Analysis of the Single Nucleotide Polymorphisms (SNPs) and Zygomorphic Flower Development in Pea (Pisum sativum L.).

Pea (Pisum sativum L.) is a model plant that has been used in classical genetics and organ development studies. However, its large and complex genome has hindered research investigations in pea. Here, we generated transcriptomes from different tissues or organs of three pea accessions using next-generation sequencing to assess single nucleotide polymorphisms (SNPs), and further investigated petal differentially expressed genes to elucidate the mechanisms regulating floral zygomorphy. Eighteen samples were sequenced, which yielded a total of 617 million clean reads, and de novo assembly resulted in 87,137 unigenes. A total of 9044 high-quality SNPs were obtained among the three accessions, and a consensus map was constructed. We further discovered several dorsoventral asymmetrically expressed genes that were confirmed by qRT-PCR among different petals, including previously reported three CYC-like proliferating cell factor (TCP) genes. One MADS-box gene was highly expressed in dorsal petals, and several MYB factors were predominantly expressed among dorsal, lateral, and/or ventral petals, together with a ventrally expressed TCP gene. In sum, our comprehensive database complements the existing resources for comparative genetic mapping and facilitates future investigations in legume zygomorphic flower development.

The Turkish EndemicPseudodelphinium turcicum(Ranunculaceae): An Unusual Population ofDelphiniumwith Peloric Flowers That Has Persisted in the Wild for 20 Years

Premise of research. The Turkish endemic Pseudodelphinium turcicum (Ranunculaceae) was described by Vural et al. (2012) based on a single population found in the salt lake basin of Tuz Gölü, Konya Province. Although the authors noticed morphological similarities between the plants and Delphinium or Garidella, they highlighted unusual features, which led them to describe a new genus consisting of a single species, P. turcicum. The aim of this study is to investigate the morphological particularities and evolution of Pseudodelphinium.Methodology. We carried out morphological, anatomical, and palynological studies on individuals of P. turcicum. We also conducted a molecular phylogenetic analysis to identify the closest relatives of this species.Pivotal results. This combination of approaches shows that the species belongs in the group of Mediterranean species in Delphinium subg. Delphinium. Based on our sampling, P. turcicum is more precisely sister to the Turkish endemic Delphinium venulosum. The perianth of P. turcicum flowers consists of tepals that are, anatomically speaking, similar to the sepals of Delphinium. A second type of perianth organs was evidenced. They are located between the tepals and the stamens, and their development is arrested at an early stage, therefore being comparable to the ventral petals of Delphinium flowers. The pollen of P. turcicum is heteromorphic.Conclusions. We conclude that the population of P. turcicum is an unusual population of Delphinium presenting peloric flowers (through ventralization) that has been maintained in the wild for at least two decades. We provide hypotheses concerning the identity of the floral organs, as well as an explanation for the origin of the particular floral morphology.

Association between Petal Form Variation and CYC2-like Genotype in a Hybrid Line of Sinningia speciosa.

This study used three-dimensional (3D) micro-computed tomography (μCT) imaging to examine petal form variation in a hybrid cross of Sinningia speciosa between a cultivar with actinomorphic flowers and a variety with zygomorphic flowers. The major objectives were to determine the genotype–phenotype associations between the petal form variation and CYCLOIDEA2-like alleles in S. speciosa (SsCYC) and to morphologically investigate the differences in petal types between actinomorphic and zygomorphic flowers. In this study, μCT was used to accurately acquire 3D floral images. Landmark-based geometric morphometrics (GM) was applied to evaluate the major form variations of the petals. Nine morphological traits of the petals were defined according to the form variations quantified through the GM analysis. The results indicated that the outward curvature of dorsal petals, the midrib asymmetry of lateral petals, and the dilation of ventral region of the tube were closely associated with the SsCYC genotype. Multiple analyses of form similarity between the petals suggested that the dorsal and ventral petals of actinomorphic plants resembled the ventral petals of zygomorphic plants. This observation indicated that the transition from zygomorphic to actinomorphic flowers in S. speciosa might be caused by the ventralization of the dorsal petals. We demonstrated that the 3D-GM approach can be used to determine genotype–phenotype associations and to provide morphological evidence for the transition of petal types between actinomorphic and zygomorphic flowers in S. speciosa.

Temporal, but not spatial, changes in expression patterns of petal identity genes are associated with loss of papillate conical cells and the shift to bird pollination in Macaronesian Lotus (Leguminosae).

In the generally bee-pollinated genus Lotus a group of four species have evolved bird-pollinated flowers. The floral changes in these species include altered petal orientation, shape and texture. In Lotus these characters are associated with dorsiventral petal identity, suggesting that shifts in the expression of dorsal identity genes may be involved in the evolution of bird pollination. Of particular interest is Lotus japonicus CYCLOIDEA 2 (LjCYC2), known to determine the presence of papillate conical cells on the dorsal petal in L.japonicus. Bird-pollinated species are unusual in not having papillate conical cells on the dorsal petal. Using RT-PCR at various stages of flower development, we determined the timing of expression in all petal types for the three putative petal identity genes (CYC-like genes) in different species with contrasting floral morphology and pollination syndromes. In bird-pollinated species the dorsal identity gene, LjCYC2, is not expressed at the floral stage when papillate conical cells are normally differentiating in bee-pollinated species. In contrast, in bee-pollinated species, LjCYC2 is expressed during conical cell development. Changes in the timing of expression of the above two genes are associated with modifications in petal growth and lateralisation of the dorsal and ventral petals in the bird-pollinated species. This study indicates that changes in the timing, rather than spatial distribution, of expression likely contribute to the modifications of petal micromorphology and petal size during the transition from bee to bird pollination in Macaronesian Lotus species.

Control of Floret Symmetry by RAY3, SvDIV1B, and SvRAD in the Capitulum of Senecio vulgaris

All members of Asteraceae, the largest flowering family, have a unique compressed inflorescence known as a capitulum, which resembles a solitary flower. The capitulum often consists of bilateral (zygomorphic) ray florets and radial (actinomorphic) disc florets. In Antirrhinum majus, floral zygomorphy is established by the interplay between dorsal petal identity genes, CYCLOIDEA (CYC) and RADIALIS (RAD), and a ventral gene DIVARICATA (DIV). To investigate the role of CYC, RAD, and DIV in the development of ray and disc florets within a capitulum, we isolated homologs of these genes from an Asteraceae species, Senecio vulgaris (common groundsel). After initial uniform expression of RAY3 (CYC), SvRAD, and SvDIV1B in ray florets only, RAY3 and SvRAD were exclusively expressed in the ventral petals of the ray florets. Our functional analysis further showed that RAY3 promotes and SvDIV1B represses petal growth, confirming their roles in floral zygomorphy. Our results highlight that while floral symmetry genes such as RAY3 and SvDIV1B appear to have a conserved role in petal growth in both Senecio and Antirrhinum, the regulatory relationships and expression domains are divergent, allowing ventral petal elongation in Senecio versus dorsal petal elongation in Antirrhinum In S vulgaris, diversification of CYC genes has led to novel interactions; SvDIV1B inhibits RAY3 and SvRAD, and may activate RAY2 This highlights how recruitment of floral symmetry regulators into dynamic networks was crucial for creating a complex and elaborate structure such as the capitulum.

Elaboration of bilateral symmetry across Knautia macedonica capitula related to changes in ventral petal expression of CYCLOIDEA-like genes.

BackgroundShifts in floral form across angiosperms, particularly from radially symmetrical to bilaterally symmetrical flowers, are often associated with shifts in speciation rates and changes in pollination syndrome. Growing evidence across both rosids and asterids indicates that CYCLOIDEA (CYC)-like transcription factors from the TCP gene family play a role in establishing the dorsoventral pattern of flower symmetry, which affects the development of both the corolla and androecium. Previous studies of CYC-like genes, especially of the CYC2 clade, indicate that these genes are dorsally restricted in bilaterally symmetrical flowers. Also, gene duplication of CYC-like genes often correlates with shifts in floral form in both individual flowers and head-like inflorescences (capitula).ResultsHere, we compared the expression patterns of six CYC-like genes from dorsal, lateral, and ventral petals of internal and external florets across capitula of Knautia macedonica (Dipsacaceae). We demonstrate that multiple copies of CYC-like genes are differentially expressed among petal types and between internal and external florets. Across paralogs, there was a general trend toward a reduction in dorsal expression and an increase in ventral expression in internal florets compared to external florets. However, it was in the ventral petals where a statistically significant increase in expression correlates with a less zygomorphic flower. We also show for the first time lateral-specific expression of a CYC-like gene. Additionally, dorsoventral asymmetric expression of a CYC3 paralog indicates that this understudied gene clade is likely also involved in floral symmetry.ConclusionsThese data indicate that the elaboration of bilateral symmetry may be regulated by the dorsoventral gradient of expression, with statistically significant changes in ventral expression correlating with changes in dorsoventral morphological specialization.Electronic supplementary materialThe online version of this article (doi:10.1186/s13227-016-0045-7) contains supplementary material, which is available to authorized users.

Differential CYCLOIDEA Expression across Developing Compound Floral Heads

Gene duplication has been implicated in the evolution of novel features across flowering plants. Of great interest has been the shift from radial to bilateral symmetry in flowers. Previous studies have demonstrated that the transcription factor CYCLOIDEA (CYC) plays an intricate role in establishing dorsal, lateral, and ventral petals, as well as in the evolution of compound floral heads (i.e., inner and outer flowers differ in symmetry). In this study, we investigated whether multiple copies of CYC differ in their expression patterns between inner and outer flowers of the compound floral heads in Knautia macedonica (Dipsacaceae). qPCR was used to determine relative expression patterns for six copies of CYC in dorsal, lateral, and ventral petals of developing inner and outer flowers. Our data show that different copies of CYC are differentially expressed in different petal types of both inner and outer flowers, with CYC2A likely playing a role in dorsal identity, and CYC2B copies involved in lateral identity. Similar patterns of gene expression were found in inner and outer flowers suggesting a dosage effect in floral head development.

Function of the CYC-Like Genes During Floral Development in Soybean

ABSTRACTFloral zygomorphy is proved to have evolved many times independently from actinomorphy, exhibiting two kinds of asymmetry, dorsoventral (DV) and organ internal (IN) asymmetry, in flowering plants. Multiple underlying regulators are involved in establishing the complex flowering mechanism during plant development. To understand how genes control the floral dorsoventral asymmetry in soybean, we isolated and analyzed the role of two different copies of CYC-like genes in Glycine max. It was demonstrated that CYClike genes, GmTCP1 and GmTCP2, encoded the TCP transcription factors that were specifically expressed in the dorsal region of floral meristem. However, the two copies were proved to be functionally divergent during petal development, and by altering the expression of CYC-like genes in transgenic soybean, similar to CYC and DICH, it was found that CYC-like genes had dorsalizing activity. The expression pattern of transgenic plants indicated that the GmTCP2 gene could specifically regulate downstream target genes such as RAD-like and DIV-like genes in the dorsal, lateral and the ventral petals. The relative expression of CUC1 and CUC2 varied in the three different kinds of petals: it was high in the dorsal petals, but low in the ventral petals. At the same time, the expression level of GmTCP1 and GmTCP2 was equally very low. In addition, the study of transgenic Arabidopsis showed that GmTCP2 could play a significant role in cell division during the whole development of plants.

Diversification of CYCLOIDEA expression in the evolution of bilateral flower symmetry in Caprifoliaceae and Lonicera (Dipsacales)

The expression of floral symmetry genes is examined in the CYCLOIDEA lineage following duplication, and these are linked to changes in flower morphology. The study focuses on Dipsacales, comparing DipsCYC2 gene expression in Viburnum (radially symmetrical Adoxaceae) to members of early-diverging lineages of the bilaterally symmetrical Caprifoliaceae (Diervilla and Lonicera). Floral tissue from six species, which included dorsal, lateral and ventral regions of the corolla, was dissected. RNA was extracted from these tissues and each copy of DipsCYC2 was amplified with reverse transcriptase PCR. Members of DipsCYC2 were expressed across the corolla in the radially symmetrical Viburnum plicatum. A shift to bilaterally symmetrical flowers at the base of the Caprifoliaceae was accompanied by a duplication of the DipsCYC2 gene, resulting in DipsCYC2A and DipsCYC2B, and by loss of expression of both of these copies in the ventral petal. In Lonicera (Caprifolieae), there is a shift from flowers with two dorsally and three ventrally oriented corolla lobes to a clear differentiation of dorsal, lateral and ventral lobes. This shift entailed a decoupling of expression of DipsCYC2A and DipsCYC2B; DipsCYC2B continues to be expressed in the dorsal and lateral lobes, while DipsCYC2A expression is restricted to just the two dorsal lobes. A reversion to more radially symmetrical flowers within Lonicera was accompanied by a re-expansion of expression of both DipsCYC2A and DipsCYC2B. The transition to bilateral symmetry in Caprifoliaceae involved: (a) duplication of an ancestral DipsCYC2 gene; (b) the loss of expression of both of these copies in the ventral petal; and (c) changes in the zone of expression, with one copy continuing to be expressed across the dorsal and lateral petals, and the other copy becoming restricted in expression to the dorsal corolla lobes.

Genetic Control of Organ Shape and Tissue Polarity

Author SummaryGenes are known to control the shape of biological structures, like flowers, hearts, and limbs, yet how they do this is poorly understood. A working hypothesis is that genes control shape by modulating local rates at which growing tissue deforms. Evaluating this idea has been difficult, however, because of the dynamic interactions that occur within growing and deforming tissue. To address this problem, we used a combination of experimental and mathematical modelling approaches to study how genes control shape in the Snapdragon flower. This system has the advantages of having well defined genes that influence shape and being accessible to growth analysis. We first tried to explain the experimental data with a model in which genes influence local rates of tissue growth. While this model could capture many aspects of flower development, it failed to account for some key features. These could be most readily explained if genes also affect an internal field of orientations along which growth is directed, established by organisers of tissue polarity. Our analysis therefore revealed a previously unsuspected role of shape genes in the control of tissue polarity, highlighting the importance of this process for the development and evolution of tissue forms.