冬虫夏草菌3个细胞核蛋白编码基因的分子进化

【目的】分析3个细胞核蛋白编码基因(csp1、MAT1-1-1和MAT1-2-1)在不同冬虫夏草菌株间的分子进化。【方法】从125个冬虫夏草样品中分别扩增csp1、MAT1-1-1和MAT1-2-1基因序列，比较外显子和内含子间以及2个交配型基因间的序列变异程度，比较基于不同基因或基因区域所构建的系统发育树拓扑结构的差异，分析3个基因承受的选择压力和DNA重组情况。【结果】3个蛋白编码基因外显子区的长度在不同菌株间高度保守，具有4.5%?5.7%的变异位点；内含子区的长度在不同菌株间相同或不同，具有1.8%?22%的变异位点。对于2个交配型基因，MAT1-1-1的碱基变异率低于MAT1-2-1。基于外显子与内含子构建的系统发育树的拓扑结构，以及基于2个交配型基因外显子构建的系统发育树的拓扑结构都存在明显差异。3个蛋白编码基因都经历着净化选择作用。基因内部的不同DNA位点间有重组，但3个基因片段之间没有明显的重组发生。【结论】由于冬虫夏草菌不同基因以及基因的不同区域表现出进化上的差异，所以在开展冬虫夏草菌进化相关的研究时，应该联合使用多个不同的基因片段。

Molecular evolution of three protein-coding genes in the Chinese caterpillar fungus Ophiocordyceps sinensis

Objective] To analyze the molecular evolution of three protein-coding genes (csp1, MAT1-1-1 and MAT1-2-1) among various Ophiocordyceps sinensis isolates. Methods] We amplified partial csp1 fragment and complete MAT1-1-1 and MAT1-2-1 gene sequences from 125 broadly sampled O. sinensis isolates, and compared the topological difference of phylogenetic trees constructed by exons and introns, and of those constructed by MAT1-1-1 and MAT1-2-1. We also measured selection pressures and detected evidence of recombination for the three genes. Results] The length of exons of the three protein-coding genes was conserved among different O. sinensis isolates with 4.5%?5.7% of variable sites. The length of introns was either identical or different among different isolates with more than 1.8%?22% of variable sites. For the two mating-type genes, MAT1-1-1 was less variable than MAT1-2-1. Phylogenetic topology differences were significant between exons and introns, and between MAT1-1-1 and MAT1-2-1 exon sequences. Each of the three genes was undergoing purified selection. Recombination events were detected between different DNA sites within each gene, but not obvious between different gene fragments. Conclusion] Because different gene fragments and different regions of a gene in O. sinensis might be evolutionarily different, we should use multiple gene fragments in future evolution-related studies in O. sinensis.