Perianth phyllotaxis and symmetry in Lamiales

Abstract

ABSTRACT Genetic studies of floral development have essentially focused on events within the floral meristem. By contrast, phyllotaxis models have shown that sepal arrangement is determined by the structure of the inflorescence. In this study, we assess the interplay between the genetic program underlying floral symmetry and phyllotaxic determination, which together shape the flower. We used a phyllotaxic model for the initiation of sepals and petals in six species of Lamiales and studied the impact of the zygomorphic genetic program on their pattern at anthesis. The initiation pattern of floral organs is determined by hormone signaling and contact pressure acting during organogenesis, while the genetic program underlying zygomorphy forces the bilateral symmetry of the initiation of organ primordia. The integration of phyllotaxic and genetic studies allows to deepen our understanding of the mechanisms producing actinomorphic or zygomorphic flowers. In any case, these mechanisms respect Curie’s symmetry principle which states that “when certain causes (here, expression of CYC-like genes) produce certain effects, the elements of symmetry of the causes must be found in the effects produced (here, perianth symmetry)”.