Arabidopsis : Flower Development and Patterning

Abstract

Abstract The development of flowers and floral organs is directed by intricate genetic programmes, many aspects of which appear to be shared among all angiosperms. Early acting genes establish floral meristem identity in lateral organ primordia initiated at the periphery of the shoot apical meristem. Later, floral organ primordia arise at precise positions within these floral meristems and take on one of the four distinct identities (sepals, petals, stamens and carpels). A simple model (ABCE model), supported by both molecular and genetic experiments in Arabidopsis , explains how a small number of regulatory genes act in different combinations to specify these different organ types. These regulatory genes encode transcription factors that control the expression of many target genes responsible for organogenesis. Key concepts Lateral organs produced by the shoot apical meristem during reproductive development acquire their identity as flowers through the action of floral meristem identity genes such as LEAFY and APETALA1 . The identities of each of the four organ types of a flower (sepal, petal, stamen and carpel) is conferred by a unique combination of floral organ identity gene activities, referred to as class A, B, C and E in the ABCE model. The activities of the class A, B, C and E genes are restricted to particular regions within a developing flower primarily, but not exclusively, through transcriptional regulation. The proteins encoded by the class A, B, C and E genes encode transcription factors that form multimeric transcriptional regulatory complexes that control the expression of distinct sets of genes. Many aspects of the genetic programmes conferring floral meristem identity and floral organ identity are conserved among all angiosperms.