Evolution of floral symmetry: a state of the art.

The genetic determinants of the organisation and variation of the flower, a striking feature of the angiosperms, are only beginning to be deciphered. Floral symmetry has recurrently evolved among angiosperms, zygomorphy (monosymmetry) being a key innovation due to its role in the plant-pollination interaction. As such, it represents a case study for evo-devo. Phylogenetic comparative studies conducted in two eudicot clades, the Ranunculales and the Asteridae sensu APGII, have shown that the evolution of this trait is dependent upon the architectural context of the flower. Genetic and developmental bases of zygomorphy have been investigated in several unrelated model species. In all these species, zygomorphy appears to be controlled, at least partially, by genes belonging to the TCP gene family of transcription factors and named CYC-like genes. Exploring the molecular bases of zygomorphy in non-model species spanning the diversity of angiosperms, but also the developmental processes involved, are now essential to understand the evolution of floral symmetry.