球孢白僵菌种内比较线粒体基因组学分析

Intraspecific comparison of mitochondrial genomes in the entomopathogenic fungus Beauveria bassiana

摘要:

[目的] 明确球孢白僵菌种内线粒体基因组的分化程度。[方法] 从GenBank下载已知的球孢白僵菌6个菌株线粒体基因组序列，详细分析基因组的组成结构，比较外显子区、内含子区和基因间区的碱基变异情况，分析菌株间的系统发育关系。[结果] 球孢白僵菌不同菌株的线粒体基因组大小为28.8-32.3 kb，都有14个常见的核心蛋白编码基因、2个rRNA基因和25个tRNA基因，具有很强的共线性关系。但是，不同菌株含有的线粒体内含子数目存在差异（2-5个/菌株），在cox1、cox2和nad1基因中表现出内含子插入/缺失多态性，这是导致线粒体基因组大小变化的主要因素。对外显子、内含子和基因间区的碱基变异情况进行分析，发现内含子和基因间区相对变异较大，而外显子区相对变异较小。系统发育分析发现，这些球孢白僵菌菌株以很高的支持度聚在一起，具有相同内含子分布规律的菌株也具有较近的聚类关系。[结论] 本研究首次报道球孢白僵菌因内含子数目不同、插入缺失突变和单核苷酸变异等在线粒体基因组上表现出较大程度的遗传分化，为认识真菌种内线粒体基因组分化提供了新的证据。

Abstract:

[Objective] To understand the intraspecific genetic differentiation of mitochondrial genomes (mitogenomes) in Beauveria bassiana.[Methods] Mitogenomes of six isolates of B. bassiana were downloaded from GenBank. Composition and structure of these mitogenomes, nucleotide variations at exonic, intronic and intergenic regions were compared. Phylogenetic relationship of these isolates was analyzed based on common core protein-coding genes.[Results] The mitogenome size of different isolates of B. bassiana ranged from 28.8 to 32.3 kb. There were 14 common core protein-coding genes, 2 rRNA genes and 25 tRNA genes in all of these mitogenomes, showing a strong collinear relationship. However, the number of introns in different isolates varied (2 to 5 introns per isolate). Intron insertion/deletion polymorphism was found in cox1, cox2 and nad1, as the main factor contributing to variations of mitogenome size. Based on nucleotide variations at exonic, intronic and intergenic regions, the relative variability at intronic and intergenic regions was larger than that at exonic regions. Phylogenetic analysis revealed that these isolates of B. bassiana grouped together with a high support value, and isolates with identical intron distribution tended to cluster closely.[Conclusion] B. bassiana shows genetic differentiation in its mitogenome due to intron number variations, indel and single nucleotide polymorphism. Our data provide new evidence for understanding the differentiation of mitogenomes in fungal species.