猛禽类15种鸟类线粒体tRNA基因序列及二级结构的比较研究

Compariative Study of Mitochondrial tRNA Gene Sequence and Secondary Structure Among Fifteen Predatory Birds

利用PCR方法扩增 13个猛禽类物种线粒体基因组中 3个主要的tRNA基因簇 :IQM (tRNAIle tRNAGln tRNAMet)、WANCY (tRNATrp tRNAAla tRNAAsn tRNACys tRNATyr)和HSL (tRNAHis tRNASer(AGY) tRNALeu(CUN) ) ,测序后结合GenBank已登陆的游隼和普通相应序列探讨猛禽类共 15种鸟类的分子系统进化。 3个目的片段长度分别为2 12～ 2 14bp、35 3～ 36 2bp、2 0 5～ 2 0 8bp ,通过比较这些tRNA基因序列和二级结构差异 ,发现可变核苷酸位点占47% ,这些变异中 6 7%出现在环区 ,且存在插入和 (或 )缺失。茎区相对保守 ,其中一些变异如双链的互补性碱基突变、G U配对等对于维系tRNA二级结构的稳定性非常重要。以夜鹰为外群分别构建了 15个猛禽类物种共 11个线粒体tRNA基因全序列和茎区序列的NJ树和MP树 ,其中基于全序列的系统发育树分支具有较高的自引导值 ,因此该数据集所反映的猛禽类系统发育关系可能更接近真实水平。系统发育分析显示 ,隼形目鹰科更接近于鸱科而不是隼科 ,而草科的分类地位也与传统的形态学和DNA DNA杂交数据的结论存在分歧。比较物种间tRNA基因二级结构发现 ,部分tRNA基因中的核苷酸插入和缺失特征在科水平具有共同衍征 ,提示这些特征对于猛禽类科间系统发育关系具有较高的参考价值。

Three major clusters of mitochondrial tRNA genes (tRNA^(Ile)-tRNA^(Gln)-tRNA^(Met), tRNA^(Trp)- tRNA^(Ala)-tRNA^(Asn)-(tRNA^(Cys))-tRNA^(Tyr) and tRNA^(His)-tRNA^(Ser(AGY))-tRNA^(Leu(CUN))) from 13 species of Predatory birds were amplified and sequenced. The length of these tRNA clusters was similar among species (212～214 bp, 353～362 bp, 205～208 bp, respectively), and 47% of the sequences were variable, 67% of which were involved in the loop regions. The stem regions were relatively conserved, and the variable base pairs were under the restriction of compensatory changes or G-U wobble pairing which could be regarded as mechanisms for maintaining a stable secondary structure. Maximum-parsimony (MP) and Neighbor joining (NJ) phylogenetic trees were constructed using all the tRNA gene sequences or stem-forming nucleotides with Caprimulgus indicus as outgroup. We found that the bootstrap values for branches of trees using the tRNA sequences were commonly higher than the others, therefore the phylogenetic relationship of Predatory birds reflected by these data may be closer to the truth. Phylogenetic analyses indicated that Accipitridae was closer to Strigidae instead of Falconidae, and the classification of Tytonidae was different from the conclusion from the previously morphological and DNA-DNA hybridization studies. By comparing the secondary structure among taxa we found that the characters of nucleotide insertions and deletions in some tRNA genes have synapomorphies, suggesting that these characters may be useful for resolving the phylogenetic relationship of different families in Predatory birds with higher phylogenetic performance.