Trends in flower symmetry evolution revealed through phylogenetic and developmental genetic advances

Abstract

A striking aspect of flowering plant (angiosperm) diversity is variation in flower symmetry. From an ancestral form of radial symmetry (polysymmetry, actinomorphy), multiple evolutionary transitions have contributed to instances of non-radial forms, including bilateral symmetry (monosymmetry, zygomorphy) and asymmetry. Advances in flowering plant molecular phylogenetic research and studies of character evolution as well as detailed flower developmental genetic studies in a few model species (e.g. Antirrhinum majus , snapdragon) have provided a foundation for deep insights into flower symmetry evolution. From phylogenetic studies, we have a better understanding of where during flowering plant diversification transitions from radial to bilateral flower symmetry (and back to radial symmetry) have occurred. From developmental studies, we know that a genetic programme largely dependent on the functional action of the CYCLOIDEA gene is necessary for differentiation along the snapdragon dorsoventral flower axis. Bringing these two lines of inquiry together has provided surprising insights into both the parallel recruitment of a CYC -dependent developmental programme during independent transitions to bilateral flower symmetry, and the modifications to this programme in transitions back to radial flower symmetry, during flowering plant evolution.

Contemporary and future studies in plant speciation, morphological/floral evolution and polyploidy: honouring the scientific contributions of Leslie D. Gottlieb to plant evolutionary biology

“…The papers by Hileman [115] and Wessinger et al [116] consider floral evolution at different taxonomic scales, the former taking a broad perspective of floral symmetry in angiosperms, and the latter focusing on two species in the genus Penstemon. Gottlieb's interests and published work have significant elements in common with the topics of both papers.…”

Evolution of floral diversity: genomics, genes andgamma

“…In radially symmetrical groups, the five petals are identical in form and equidistant from each other, but there have been frequent transitions to bilateral symmetry in which the petals act as three separate modules (dorsal, lateral and ventral). Floral symmetry genes appear to function in these three modules of the flower independently to produce complex petal arrangements-a phenomenon with multiple, independent derivations [96,97]. The primary genetic regulators of floral symmetry are the CYCLOIDEA (CYC) TCP domain transcription factors and the MYB domain transcription factors DIVARICATA (DIV) and RADIALIS (RAD) [28,96].…”

“…Floral symmetry genes appear to function in these three modules of the flower independently to produce complex petal arrangements-a phenomenon with multiple, independent derivations [96,97]. The primary genetic regulators of floral symmetry are the CYCLOIDEA (CYC) TCP domain transcription factors and the MYB domain transcription factors DIVARICATA (DIV) and RADIALIS (RAD) [28,96]. Phylogenetic analyses suggest that the CYC, DIV and RAD genes expanded into two or three paralogous lineages prior to the origin of Pentapetalae [98][99][100] and the three CYC clades may have been established through duplications between the divergence of Proteales and the diversification of Gunneridae [101].…”

Conversion of Abaxial to Adaxial Petal in a Torenia (<i>Torenia fournieri</i> Lind. ex Fourn.) Mutant Appeared in Selfed Progeny of the Mutable Line “Flecked”

“…Novel flower morphology developed by breeding is attractive to consumers. Flower symmetry is an important morphological factor influencing the appearance and impression of flowers (Endress, 1999;Hileman, 2014), and is classified by the number of symmetry axes passing through the corolla center. Actinomorphic flowers have multiple (at least two) symmetry axes, zygomorphic flowers have a single axis, and asymmetrical flowers have no symmetry axis (Hileman, 2014).…”

“…Flower symmetry is an important morphological factor influencing the appearance and impression of flowers (Endress, 1999;Hileman, 2014), and is classified by the number of symmetry axes passing through the corolla center. Actinomorphic flowers have multiple (at least two) symmetry axes, zygomorphic flowers have a single axis, and asymmetrical flowers have no symmetry axis (Hileman, 2014). Zygomorphic flowers evolved from actinomorphic flowers to attract specialized pollinators in a step that may have occurred independently in many species of angiosperms (Donoghue et al, 1998;Endress, 1999).…”