The Arabidopsis flower is composed of four concentric whorls of organs: the sepals, petals, stamens and carpels. The development of this pattern depends on two general processes: that of establishing a florally determined meristem, and that of establishing particular organ identities. Mutational analyses have been instrumental in defining classes of genes that participate in each of these processes. The floral meristem identity genes are required to specify a florally determined meristem, and also appear to be required in part to activate the floral homeotic genes. The floral homeotic genes function in discrete regions of the florally determined meristem to specify the different organ types. The molecular analysis of these genes is beginning to shed light on the details of their regulation and function. The challenge that remains is to understand how the action of these genes in the dividing meristematic cell population can be coordinated and maintained to result in the differentiation of the complex array of cell and tissue types that make up the Arabidopsis flower.
