Functional and evolutionary significance of the Bsister genes in flowering plants

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Class B floral organ identity genes (‘B genes’) are homeotic MADS-box genes which specify petal and stamen identity during floral development. Bsister (Bs) genes are representing the putative sister clade of the B genes and were isolated from several angiosperms and gymnosperms indicating that this MADS-box gene clade originated more than 300 million years ago. Bs genes are predominantly expressed in female reproductive organs of both angiosperms and gymnosperms, suggesting an important role in ovule development. However, mutant alleles of one of the Arabidopsis Bs genes (abs/tt16) reveal only mild phenotypic effects in seed coat pigmentation and endothelium development. Taking together the high degree of conservation on both gene sequence and expression level we assume a more profound function of Bs genes in flower development than recognized so far. To test this hypothesis, we will analyze possible redundancies with AGL63, the only other Bs gene in the Arabidopsis genome and with the B genes. We will learn more about the evolutionary significance of Bs genes by functional analysis of Bs genes from the basal eudicot California poppy and from the monocot rice. Spanning a large degree of angiosperm diversity by analyzing three representative species we will aim at understanding the functional dynamics of Bs genes during angiosperm evolution.