杂交构树Ty3-gypsy类逆转座子逆转录酶序列的多样性分析

Diversity Analysis of Ty3-gypsy-like Retrotransposon Reverse Transposases in Broussonetia papyrifera L. Vent.

为深入分析杂交构树的遗传多样性,开发可靠的分子标记,采用同源克隆技术分离了Ty3-gypsy类逆转座子逆转录酶序列,并对其同源性及系统进化关系进行了分析。所分离的40条序列(命名为BpRT1-40)长度为410～420 bp,均富含AT碱基,序列间的同源性范围为14.2%～99.3%,显示较高异质性。氨基酸序列分析发现,其中有19条序列发生了终止密码子突变、9条发生了移框突变,表明终止密码子突变和移框突变可能是导致杂交构树逆转座子异质性的主要原因。系统进化分析显示:该40条氨基酸序列由2个基因家族组成,其中FamilyⅠ包含38条序列,由5个亚家族组成,各亚家族成员间亲源关系较近;FamilyⅡ包含2条序列,它们与其它序列亲缘关系较远。与其他植物Ty3-gypsy类逆转座子逆转录酶进行系统进化分析发现,所克隆的序列与绿豆、荸荠、兴安落叶松、皱皮椒草、油棕、黄瓜、向日葵等植物的Ty3-gypsy类逆转座子逆转录酶序列具有较近的亲缘关系。以上结果说明:FamilyⅠ是杂交构树中广泛存在的逆转座子家族,它们可能在杂交构树的遗传进化中发挥着重要的作用。FamilyⅡ中的2条序列同源性较低,同时与其它物种的Ty3-gypsy类逆转座子转录酶的遗传距离也较远,由此可以说明FamilyⅡ的起源比较古老,特异性强。本研究为进一步合理地利用杂交构树资源提供理论基础。

To further analyze the genetic diversity of Broussonetia papyrifera, and develop credible molecular marker, reverse transposases of Ty3-gypsy-like retrotransposons were isolated by homology-based cloning technology, and their homology and phylogenetic relation were analyzed. The length of the nucleotide sequences of the 40 isolated fragments （named as BpRT1-40） varied from 410 to 420 bp with rich AT content, and their homology ranged from 14.2%-99.3%, showing a high heterogeneity. Amino acid sequence analysis showed that termination codon mutation occurred in nineteen sequences and frameshift mutation occurred in nine sequences, suggesting that termination codon mutation and frameshift mutation might be the major reasons resulted in heterogeneity of retrotransposons in B. papyrifera. Phylogenetic analysis showed that the 40 nucleotide sequences consisted of two gene families, and the family Ⅰ contained 38 sequences, which consisted of 5 subfamilies, and the sequences of the subfamilies had close relationships with each other; family Ⅱ contained 2 sequences which showed far relationship with each other. Phylogenetic analysis of the isolated sequences and Ty3-gypsy-like reverse transcriptases from the other plant species found that the cloned sequence had a close relationship with those from Vigna radiata, Eleocharis palustris, Larix grnelinii, Peperomia caperata, Elaeis guineensis, Cucumis hystrix, and Orobanche cernua. These results suggested that the family Ⅰ retrotransposons existed widely in B. papyrifera and they might play an important role in genetic evolution orB. popyrifera. The 2 sequences of family Ⅱ had low homology between each other and far genetic distances with reverse transposases from other plants as well, revealing that family Ⅱ had ancient origin and high specificity. This study could provide a theoretical basis for further rational utilization of Broussonetia papyrifera resources.