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

Abstract Background Shifts 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). Results Here, 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. Conclusions These 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

Specific duplication and dorsoventrally asymmetric expression patterns of Cycloidea-like genes in zygomorphic species of Ranunculaceae.

Floral bilateral symmetry (zygomorphy) has evolved several times independently in angiosperms from radially symmetrical (actinomorphic) ancestral states. Homologs of the Antirrhinum majus Cycloidea gene (Cyc) have been shown to control floral symmetry in diverse groups in core eudicots. In the basal eudicot family Ranunculaceae, there is a single evolutionary transition from actinomorphy to zygomorphy in the stem lineage of the tribe Delphinieae. We characterized Cyc homologs in 18 genera of Ranunculaceae, including the four genera of Delphinieae, in a sampling that represents the floral morphological diversity of this tribe, and reconstructed the evolutionary history of this gene family in Ranunculaceae. Within each of the two RanaCyL (Ranunculaceae Cycloidea-like) lineages previously identified, an additional duplication possibly predating the emergence of the Delphinieae was found, resulting in up to four gene copies in zygomorphic species. Expression analyses indicate that the RanaCyL paralogs are expressed early in floral buds and that the duration of their expression varies between species and paralog class. At most one RanaCyL paralog was expressed during the late stages of floral development in the actinomorphic species studied whereas all paralogs from the zygomorphic species were expressed, composing a species-specific identity code for perianth organs. The contrasted asymmetric patterns of expression observed in the two zygomorphic species is discussed in relation to their distinct perianth architecture

Radial or bilateral? The molecular basis of floral symmetry.

In the plant kingdom, the flower is one of the most relevant evolutionary novelties. Floral symmetry has evolved multiple times from the ancestral condition of radial to bilateral symmetry. During evolution, several transcription factors have been recruited by the different developmental pathways in relation to the increase of plant complexity. The MYB proteins are among the most ancient plant transcription factor families and are implicated in different metabolic and developmental processes. In the model plant Antirrhinum majus, three MYB transcription factors (DIVARICATA, DRIF, and RADIALIS) have a pivotal function in the establishment of floral dorsoventral asymmetry. Here, we present an updated report of the role of the DIV, DRIF, and RAD transcription factors in both eudicots and monocots, pointing out their functional changes during plant evolution. In addition, we discuss the molecular models of the establishment of flower symmetry in different flowering plants

An expanded evolutionary role for flower symmetry genes

CYCLOIDEA (CYC)-like TCP genes are critical for flower developmental patterning. Exciting recent breakthroughs, including a study by Song et al. published in BMC Evolutionary Biology, demonstrate that CYC-like genes have also had an important role in the evolution of flower form. See research article http://www.biomedcentral.com/1471-2148/9/244 webcite

Understanding the Genetic Basis of Floral Diversity

The major radiations that punctuate angiosperm evolution are often associated with innovations in floral architecture. The field of plant developmental evolution seeks to understand the generation of this diversity using comparative genetic approaches that build on work done in model species such as Arabidopsis. This strategy has been particularly successful when applied to the genetic program controlling floral organ identity, but is also making advances in the area of floral symmetry. As useful as the "candidate gene" approach has been, alternatives are required to investigate morphological phenomena that are not represented in model species. Other options include methods based on quantitative trait loci and DNA sequencing, which have the additional benefit of facilitating the development of new model species. The combination of all of these approaches across a wide range of species has the potential to elucidate the genetic underpinnings of both recent and ancient radiations of flowering plants.a wide range of species has the potential to elucidate the genetic underpinnings of both reeent and ancient radiations of flowering plants.Organismic and Evolutionary Biolog

An investigation of large-leaved Gunnera L. (Gunneraceae) grown outside in Britain and Ireland

A molecular investigation of large-leaved Gunnera growing outside in Britain and Ireland was conducted. Two low-copy nuclear CYCLOIDEA-like genes (CYC-like 1 and CYC-like 2) and two chloroplast DNA regions (matK and psbD-trnT) were sequenced for 271 samples of Gunnera. While it was confirmed that genuine G. tinctoria is growing both in cultivation and in the wild, the results support recently published morphological and historical findings that the species G. manicata appears no longer to be present in Britain and Ireland. Instead, the plant under this name is G. × cryptica, a hybrid between G. manicata and G. tinctoria. The implication of this discovery for legislation on invasive non-native species where G. manicata and G. tinctoria are listed is explored

Interpreting lemma and palea homologies: a point of view from rice floral mutants

In contrast to eudicot flowers which typically exhibit sepals and petals at their periphery, the flowers of grasses are distinguished by the presence of characteristic outer organs. In place of sepals, grasses have evolved the lemma and the palea, two bract-like structures that partially or fully enclose the inner reproductive organs. With little morphological similarities to sepals, whether the lemma and palea are part of the perianth or non-floral organs has been a longstanding debate. In recent years, comparative studies of floral mutants as well as the availability of whole genome sequences in many plant species have provided strong arguments in favor of the hypothesis of lemma and palea being modified sepals. In rice, a feature of the palea is the bending of its lateral region into a hook-shaped marginal structure. This allows the palea to lock into the facing lemma region, forming a close-fitting lemma-palea enclosure. In this article, we focus on the rice lemma and palea and review some of the key transcription factors involved in their development and functional specialization. Alternative interpretations of these organs are also addressed