玉米性别决定基因TASSELSEED2及其同源基因的分子进化特征

Molecular evolutionary characteristics of maize TASSELSEED2 and homologous genes in plant species

TS2是最早在玉米中发现的性别决定基因,但是在其他的单性花或者两性花的被子植物中其同源基因是否也与花的性别形成有关以及其进化特征仍不清楚.以玉米性别决定基因TASSELSEED2(TS2)为检索序列,通过BLAST搜索得到21个测序植物物种的27个TS2同源基因,并利用生物信息学和比较基因组学方法详细分析了这些TS2基因的序列特征、进化关系及选择压力.结果表明,植物TS2基因具有3种基因结构类型、2种典型的功能结构域和7种保守基序组织模式,且单性花和两性花植物间并没有表现出特异性.系统进化树显示,以江南卷柏TS2蛋白为系统树基部,除了PtrTS2b、SlaTS2、CsaTS2和CpaTS2这4种单性花的TS2蛋白外,剩余22个植物TS2蛋白被划分为4个亚群.值得注意的是,除杨树外,其余4种单性花植物的TS2基因距离较远,均单独为一分支.进一步对4个亚群的选择位点分析发现,这些亚群共包含出24个正选择位点(P>0.05),说明各亚群TS2基因均受控于纯净选择或松弛的纯净选择.由上述结果可知,TS2基因在进化过程中发生了多次重复和基因扩增事件,而多次独立的重复或者基因扩增事件导致TS2基因失去了对性别的决定或者调控作用.

Though TS2 is a sex determining gene initially found in maize, whether TS2 homologous genes in other monoecious and hermaphroditic plants are also related to the sex formation of flowers is not known. The evolutional characteristics of these genes are still not clear. In this study, 27 TS2 homologous genes from 21 sequenced plant genomes were identified by BLAST search using maize TS2 as query sequence, and a series of analysis were further performed, including their sequence characterization, phylogenetic relationships selective pressure, using bioinformatics and comparative genomics methods. Sequence analysis showed that TS2 genes from plants had three gene structure types, two typical functional domains and seven conserved motifs, with no specificity between monoecious and hermaphroditic plants. With SmoTS2 （Selaginellae Moellendofii） protein as root of the phylogenetic tree, phylogenetic analysis indicated that except for PtrTS2b, SlaTS2, CsaTS2 and CpaTS2 which are all from monoecious plants, the remaining 22 plant TS2 proteins could be classified into four subgroups. It was worth noting that except for PtrTS2 from Populus trichocarpa, the other four TS2 genes from monoecious plants were far from each other, each belonging to a separate clade. Further selection analysis of the four subgroups detected a total of 24 positive selection sites （P 〉 0.05）, indicating that all groups of TS2 genes were controlled by purifying selection or relaxed purifying selection. The above results indicated that plant TS2 genes underwent multiple gene duplication and amplification events, which deprived the TS2 genes of the function of sex determination or regulation. These results may provide useful clues for further investigating the plant TS2 gene function.