Corradi Nicolas, Akiyoshi Donna E, Morrison Hilary G, Feng Xiaochuan, Weiss Louis M, Tzipori Saul, Keeling Patrick J
Department of Botany, Canadian Institute for Advanced Research, University of British Columbia, Vancouver, British Columbia, Canada.
PLoS One. 2007 Dec 5;2(12):e1277. doi: 10.1371/journal.pone.0001277.
Microsporidia are intracellular parasites that are highly-derived relatives of fungi. They have compacted genomes and, despite a high rate of sequence evolution, distantly related species can share high levels of gene order conservation. To date, only two species have been analysed in detail, and data from one of these largely consists of short genomic fragments. It is therefore difficult to determine how conservation has been maintained through microsporidian evolution, and impossible to identify whether certain regions are more prone to genomic stasis.
Here, we analyse three large fragments of the Enterocytozoon bieneusi genome (in total 429 kbp), a species of medical significance. A total of 296 ORFs were identified, annotated and their context compared with Encephalitozoon cuniculi and Antonospora locustae. Overall, a high degree of conservation was found between all three species, and interestingly the level of conservation was similar in all three pairwise comparisons, despite the fact that A. locustae is more distantly related to E. cuniculi and E. bieneusi than either are to each other.
CONCLUSIONS/SIGNIFICANCE: Any two genes that are found together in any pair of genomes are more likely to be conserved in the third genome as well, suggesting that a core of genes tends to be conserved across the entire group. The mechanisms of rearrangments identified among microsporidian genomes were consistent with a very slow evolution of their architecture, as opposed to the very rapid sequence evolution reported for these parasites.
微孢子虫是细胞内寄生虫，是真菌的高度进化的近亲。它们的基因组紧凑，尽管序列进化速率很高，但远缘物种仍可共享高水平的基因顺序保守性。迄今为止，仅对两个物种进行了详细分析，其中一个物种的数据主要由短基因组片段组成。因此，很难确定微孢子虫进化过程中保守性是如何维持的，也无法确定某些区域是否更易于发生基因组稳定。
在这里，我们分析了具有医学意义的比氏肠微孢子虫基因组的三个大片段（总共429千碱基对）。总共鉴定并注释了296个开放阅读框，并将它们的背景与兔脑炎微孢子虫和蝗虫无孢子虫进行了比较。总体而言，在所有三个物种之间发现了高度的保守性，有趣的是，尽管蝗虫无孢子虫与兔脑炎微孢子虫和比氏肠微孢子虫的亲缘关系比它们彼此之间的关系更远，但在所有三个成对比较中保守性水平相似。
结论/意义：在任何一对基因组中共同发现的任何两个基因也更有可能在第三个基因组中保守，这表明一组核心基因倾向于在整个群体中保守。在微孢子虫基因组中鉴定出的重排机制与其结构的非常缓慢的进化一致，这与报道的这些寄生虫非常快速的序列进化相反。
