Uppsala BioCenter, Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
BMC Evol Biol. 2010 Jul 31;10:234. doi: 10.1186/1471-2148-10-234.
The self-fertile filamentous ascomycete Neurospora tetrasperma contains a large (approximately 7 Mbp) and young (< 6 MYA) region of suppressed recombination within its mating-type (mat) chromosomes. The objective of the present study is to reveal the evolutionary history, including key genomic events, associated with the various regions of the mat chromosomes among ten strains representing all the nine known species (lineages) contained within the N. tetrasperma species complex.
Comparative analysis of sequence divergence among alleles of 24 mat-linked genes (mat A and mat a) indicates that a large region of suppressed recombination exists within the mat chromosome for each of nine lineages of N. tetrasperma sensu latu. The recombinationally suppressed region varies in size and gene composition among lineages, and is flanked on both ends by normally recombining regions. Genealogical analyses among lineages reveals that eight gene conversion events have occurred between homologous mat A and mat a-linked alleles of genes located within the region of restricted recombination during the evolutionary history of N. tetrasperma.
We conclude that the region of suppressed recombination in the mat chromosomes has likely been subjected to independent contraction and/or expansion during the evolutionary history of the N. tetrasperma species complex. Furthermore, we infer that gene conversion events are likely a common phenomenon within this recombinationally suppressed genomic region. We argue that gene conversions might provide an efficient mechanism of adaptive editing of functional genes, including the removal of deleterious mutations, within the young recombinationally suppressed region of the mat chromosomes.
可育丝状子囊菌 Neurospora tetrasperma 含有一个较大（约 7 Mbp）且年轻（<6 MYA）的重组抑制区，位于其交配型（mat）染色体中。本研究的目的是揭示与包含在 N. tetrasperma 种复合体中的九个已知种（谱系）的所有十个菌株的 mat 染色体的各个区域相关的进化历史，包括关键基因组事件。
对代表 N. tetrasperma 种复合体所有九个谱系的十个菌株的 24 个 mat 连锁基因（mat A 和 mat a）等位基因的序列差异进行比较分析表明，每个谱系的 mat 染色体中都存在一个较大的重组抑制区。重组抑制区在大小和基因组成上在谱系之间存在差异，并且在正常重组区域的两端都受到限制。谱系之间的系统发育分析表明，在 N. tetrasperma 的进化历史中，有八个基因转换事件发生在位于限制重组区域内的同源 mat A 和 mat a 连锁等位基因之间。
我们得出结论，mat 染色体中重组抑制区的大小可能在 N. tetrasperma 种复合体的进化历史中经历了独立的收缩和/或扩张。此外，我们推断基因转换事件可能是这个重组抑制基因组区域内的一个常见现象。我们认为，基因转换可能为功能基因（包括去除有害突变）在 mat 染色体的年轻重组抑制区中提供了一种有效的适应性编辑机制。
