Control of patterning, growth, and differentiation by floral organ identity genes

In spite of the different morphologies of sepal, petals, stamen and carpels, all these floral organs are believed to be modified versions of a ground-state organ similar to the leaf. Modifications of the ground-state developmental program are orchestrated by different combinations of MADS-domain transcription factors encoded by floral organ identity genes. In recent years, much has been revealed about the gene regulatory networks controlled by the floral organ identity genes and about the genetic pathways that control leaf development. Here, I review how floral organ identity is connected with the control of morphogenesis and differentiation of shoot organs, focusing on the model species Arabidopsis thaliana. Direct links have emerged between floral organ identity genes and genes involved in abaxial-adaxial patterning, organ boundary formation, tissue growth and cell differentiation. In parallel, predictive models have been developed to explain how the activity of regulatory genes can be coordinated by intercellular signaling and constrained by tissue mechanics. Combined, these advances provide a unique opportunity to reveal how exactly leaf-like organs have been "metamorphosed" into floral organs during evolution and to reveal crucial regulatory points in the generation of plant form.