Molecular and genetic mechanisms of floral control.

In the last 15 years, knowledge of the molecular and genetic mechanisms that underlie floral induction, floral patterning, and floral organ identity has exploded. Elucidation of basic mechanisms has derived primarily from work in three dicot species: Antirrhinum majus, Arabidopsis thaliana, and Petunia hybrida. Although Antirrhinum and petunia have contributed fundamental breakthroughs to our understanding of flower development, it is from Arabidopsis that the most detailed and comprehensive picture of the molecular mechanisms underlying flower development has been obtained. In this review, I will outline the present state of knowledge, focusing on molecular and genetic mechanisms revealed in work on Arabidopsis, specifically in three areas: the integration of floral induction signals by a small group of floral integrators, the activation of the floral organ identity genes by the floral meristem identity genes, and interactions among the floral organ identity genes, particularly the A and C class genes. By choosing to focus on progress in Arabidopsis, I do not mean to suggest that work in other species is unimportant or uninformative. To the contrary, without studies in Antirrhinum and petunia, our knowledge and the broad impact of what has been learned would clearly be less. One of the satisfying things about the field of flower development is the applicability of the floral patterning mechanisms to a wide range of plant species; such a conclusion only comes from careful analysis in multiple distantly related species. The general pattern in the field has been that molecular and genetic mechanisms, based on work in model species, serve as the basis forwork in other species,many of which are of economic importance. Ultimately, the goal is to use information discovered in the model plants to engineer economically important plants for human and ecological benefit.