Evolution of 5S rRNA Genes in Ophiopogon xylorrhizus Wang et Dai and O. sylvicola Wang et Tang (Convallariaceae)  

木根麦冬与林生麦冬5SrRNA基因的进化(英文)

作　　者：牛伟[1] 张大明[1] 

机构地区：[1]中国科学院植物研究所系统与进化植物学开放研究实验室,北京100093

出　　处：《Acta Botanica Sinica》2002年第3期329-336,共8页Acta Botanica Sinica（植物学报：英文版）

基　　金：国家自然科学基金 ( 39870 0 5 5 )~~

摘　　要：To reveal how a large gene family evolved in the highly organized genome, the present study sequenced 294 copies of 5S rRNA genes from six individuals of three populations of Ophiopogon xylorrhizus Wang et Dai, and 45 copies from its closest species, O. sylvicola Wang et Tang. Based on the sequences the gene-phylogeny was inferred through PAUP. The sequences were highly diversified. Of the 339 randomly cloned copies, only 13 pairs (3.8%) were identical, with length varied between 307 - 548 bp (average 438.6 bp). The sequence differentiation index (SDI) in O. xylorrhints was 0.078, in O. sylvicola was 0.032, and between these two species was 0.149. In the most parsimonious tree reconstructed, all of the 294 copies of O. xylorrhizus were grouped into one clade, and those of O. sylvicola were grouped into another clade with 100% bootstrap support. The result demonstrated that the copies of 5S rRNA genes originated from just one progenitor copy, 'founder copy', in both of the species respectively, followed by a series of proliferation, and little, if any, homogenization ever occurred in the copies. As the common ancestor of the two species must have home multiple copies of the genes, all the other copies were lost during or after the speciation. Additionally, the phylogeny clearly showed that the founder copy was proliferated continuously through time, not just once. O. xylorrhizus is an extremely endangered species in which high genetic diversity, selfing and depression on seedlings were observed previously. In our study the sequences from different populations or different individuals were mixed in the branches of the O. xylorrhizus clade, although they evolved independently. It is assumed that gene flow of the species happened much more frequently in the past, making the proliferated copies dispersed to different populations, and the species maintained an amount of genetic diversity. Therefore, the selfing and seedling depression would be the result of a recent event. We suggest that some changes in outer mechanis为了揭示多拷贝基因的进化方式 ,对濒危植物木根麦冬 (OphiopogonxylorrhizusWangetDai) 3个居群、6个个体的 2 94个 5SrRNA基因拷贝及其姐妹种林生麦冬 (O .sylvicolaWangetTang)的 45个拷贝进行了DNA测序和序列分析 ,并以这个迄今发表的最大的单个物种的 5SrRNA基因数据 ,以PAUP程序重建了分子系统发育树。结果表明 :1)所得序列呈高度多样性 ,长度变化在 30 7～ 5 48碱基之间 ,仅 13对 (3.8%)相同 ,序列分化指数较高 :木根麦冬是 0 .0 78,林生麦冬是 0 .0 32 ,两物种间是 0 .149;2 ) 10 0 %的统计值支持两物种的 5SrRNA基因分别来自于祖先种的一个拷贝 ,即“建立者拷贝” ,这个拷贝在物种形成之后进行了一系列连续的扩增 ,形成一个直系的基因家族 ,而祖先种的其他拷贝在物种形成后被丢失 ;3)不同拷贝是独立进化的 ,序列间的一致化过程很弱 ,这在串联重复的rRNA基因中是罕见的 ;4)木根麦冬居群间曾存在频繁的基因交流 ,使 5SrRNA基因的许多拷贝扩散于不同居群 ,维持着种内较高的遗传多样性。可以认为是某些近期发生的变化 ,阻止了居群间的基因交流 ,导致该物种广泛的自交 ,发生自交衰退 ,并最后导致濒危。

关 键 词：Ophiopogon xylorrhizus Ophiopogon sylvicola 5S rRNA EVOLUTION PHYLOGENY 

分 类 号：Q941.2[生物学—植物学]