Department of Biology, Amherst College, Amherst, Massachusetts 01002, USA.
Evolution. 2012 Nov;66(11):3519-33. doi: 10.1111/j.1558-5646.2012.01703.x. Epub 2012 Jun 26.
Parallels have been drawn between the evolution of nonrecombining regions in fungal mating-type chromosomes and animal and plant sex chromosomes, particularly regarding the stages of recombination cessation forming evolutionary strata of allelic divergence. Currently, evidence and explanations for recombination cessation in fungi are sparse, and the presence of evolutionary strata has been examined in a minimal number of fungal taxa. Here, the basidiomycete genus Microbotryum was used to determine the history of recombination cessation for loci on the mating-type chromosomes. Ancestry of linkage with mating type for 13 loci was assessed across 20 species by a phylogenetic method. No locus was found to exhibit trans-specific polymorphism for alternate alleles as old as the mating pheromone receptor, indicating that ages of linkage to mating type varied among the loci. The ordering of loci in the ancestry of linkage to mating type does not agree with their previously proposed assignments to evolutionary strata. This study suggests that processes capable of influencing divergence between alternate alleles may act at loci in the nonrecombining regions (e.g., gene conversion) and encourages further work to dissect the evolutionary processes acting upon genomic regions that determine mating compatibility.
在真菌交配型染色体和动植物性染色体的非重组区域的进化过程之间已经进行了比较，特别是在停止重组形成等位基因分歧进化层的阶段。目前，真菌中重组停止的证据和解释还很缺乏，并且只在少数几种真菌类群中检查了进化层的存在。在这里，担子菌属的 Microbotryum 被用来确定交配型染色体上的重组停止的历史。通过系统发育方法，在 20 个种中评估了 13 个位点与交配型的连锁祖先。没有发现任何一个位点表现出与交配信息素受体一样古老的交替等位基因的跨种多态性，这表明各位点与交配型的连锁年龄不同。与交配型连锁的祖先中各位点的排列顺序与它们之前被分配到进化层的顺序不一致。这项研究表明，可能影响交替等位基因之间差异的过程（例如基因转换）可能作用于非重组区域中的位点，并鼓励进一步的工作来剖析决定交配相容性的基因组区域上的进化过程。
