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.

BackgroundWhile floral symmetry has traditionally been assessed qualitatively, recent advances in geometric morphometrics have opened up new avenues to specifically quantify flower shape and size using robust multivariate statistical methods. In this study, we examine, for the first time, the ability of geometric morphometrics to detect morphological differences in floral dorsoventral asymmetry following virus-induced gene silencing (VIGS). Using Fedia graciliflora Fisch. & Meyer (Valerianaceae) as a model, corolla shape of untreated flowers was compared using canonical variate analysis to knockdown phenotypes of CYCLOIDEA2A (FgCYC2A), ANTHOCYANIDIN SYNTHASE (FgANS), and empty vector controls. ResultsUntreated flowers and all VIGS treatments were morphologically distinct from each other, suggesting that VIGS may cause subtle shifts in floral shape. Knockdowns of FgCYC2A were the most dramatic, affecting the position of dorsal petals in relation to lateral petals, thereby resulting in more actinomorphic-like flowers. Additionally, FgANS knockdowns developed larger flowers with wider corolla tube openings.ConclusionsThese results provide a method to quantify the role that specific genes play in the developmental pathway affecting the dorsoventral axis of symmetry in zygomorphic flowers. Additionally, they suggest that ANS may have an unintended effect on floral size and shape.Electronic supplementary materialThe online version of this article doi: (10.1186/s12870-017-1152-x) contains supplementary material, which is available to authorized users.

No abstract

The Dipsacales is an order of plants that exhibits a striking shift from radial symmetry in basal lineages like viburnum to strong bilateral symmetry in species like honeysuckle. We are interested in determining how multiple copies of the transcription factor CYCLOIDEA (CYC) may be linked to floral symmetry shifts across Dipsacales. We use quantitative reverse transcriptase PCR (qPCR) to compare relative expression levels of the major copies of CYC (CYC1, CYC2, CYC3) across Dipsacales in seven different species exhibiting radial symmetry, bilateral symmetry, or asymmetry. Our data suggest that radially symmetric species do not exhibit wide variation in expression among petals, whereas bilateral and asymmetric flowers have pronounced differences, especially in CYC2 copiesResearch supported by NSF IOS grant 1121301.

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.