Functional and evolutionary significance of the Bsister genes in flowering plants

B类花器官鉴定基因（‘ B基因’）是在花发育过程中决定花瓣和雄蕊鉴定的同源MADS-box基因。Bsister （Bs）基因代表了被认为是B基因的姐妹分支，从几种被子植物和裸子植物中分离出来，表明这个MADS-box基因分支起源于3亿多年前。b基因在被子植物和裸子植物的雌性生殖器官中均有显著表达，提示其在胚珠发育中起重要作用。然而，拟南芥b基因之一的突变等位基因（abs/tt16）在种皮色素沉着和内皮细胞发育中仅表现出轻微的表型影响。考虑到这些基因在序列和表达水平上的高度保守性，我们认为b基因在花发育中的作用比目前所认识到的更为深刻。为了验证这一假设，我们将分析拟南芥基因组中唯一的另一个B基因AGL63和B基因之间可能的冗余。我们将通过对加利福尼亚罂粟和单子叶水稻中Bs基因的功能分析来进一步了解Bs基因的进化意义。通过分析三个具有代表性的被子植物物种，我们将在很大程度上跨越被子植物多样性，旨在了解被子植物进化过程中b基因的功能动态。

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.