Evolution and diversity of a fungal self/nonself recognition locus.
Evolution and diversity of a fungal self/nonself recognition locus.
复制标题
DOI：
10.1371/journal.pone.0014055
复制
发表时间：
2010-11-19
期刊：
影响因子：
3.7
通讯作者：
Glass NL
中科院分区：
文献类型：
--
作者：
Hall C;Welch J;Kowbel DJ;Glass NL
自我/非自我辨别是病原体识别和移植物排斥反应的基本特征，是许多生物体中普遍存在的现象。丝状真菌，如粗糙脉孢霉，由于其单倍体性质、较小的基因组和优良的遗传/基因组资源，为自我/非自我识别基因座的群体遗传/进化分析提供了模型。在粗面金线莲中，营养生长过程中的非自分辨是由11个异核体不亲和性(HET)基因座决定的。在这些het基因座上具有不同等位基因特异性的菌株之间的细胞融合会触发快速的程序性细胞死亡反应。在这项研究中，我们评估了由两个紧密连锁的基因座het-c(NCU03493)和pin-c(NCU03494)组成的非自我识别复合体的进化、群体遗传学和选择机制。Pin-c与het-c相邻的基因组位置是脉孢菌属和索氏菌属物种所特有的，在索氏菌科内与其他物种分化后由基因复制而来。粗纹夜蛾的het-c pin-c等位基因处于严重连锁不平衡状态，由het-c1/pin-c1、het-c2/pin-c2和het-c3/pin-c3三种单倍型组成，这三种单倍型在种群样本中的频率相同，且表现出跨物种的多态。重组单倍型的缺失与het-c/pin-c基因间序列的差异有关。对het-c和pin-c的正选择和平衡选择的测试支持这一结论，即这两个基因座都处于非中性平衡选择之下；两个基因的其他区域似乎都处于正选择之下。我们的数据表明，het-c2/pin-c2单倍型大约在300-1200万年前由het-c1/pin-c1和het-c3/pin-c3之间的重组事件产生。这些结果支持通过多态基因与含有HET结构域的基因的关联来形成赋予非自我歧视的基因座的模型。不同的等位基因类型可以通过重组和正选择而产生，并随后通过平衡基因间序列的选择和差异来维持，从而导致单倍型之间的重组障碍。
Self/nonself discrimination is an essential feature for pathogen recognition and graft rejection and is a ubiquitous phenomenon in many organisms. Filamentous fungi, such as Neurospora crassa, provide a model for analyses of population genetics/evolution of self/nonself recognition loci due to their haploid nature, small genomes and excellent genetic/genomic resources. In N. crassa, nonself discrimination during vegetative growth is determined by 11 heterokaryon incompatibility (het) loci. Cell fusion between strains that differ in allelic specificity at any of these het loci triggers a rapid programmed cell death response. In this study, we evaluated the evolution, population genetics and selective mechanisms operating at a nonself recognition complex consisting of two closely linked loci, het-c (NCU03493) and pin-c (NCU03494). The genomic position of pin-c next to het-c is unique to Neurospora/Sordaria species, and originated by gene duplication after divergence from other species within the Sordariaceae. The het-c pin-c alleles in N. crassa are in severe linkage disequilibrium and consist of three haplotypes, het-c1/pin-c1, het-c2/pin-c2 and het-c3/pin-c3, which are equally frequent in population samples and exhibit trans-species polymorphisms. The absence of recombinant haplotypes is correlated with divergence of the het-c/pin-c intergenic sequence. Tests for positive and balancing selection at het-c and pin-c support the conclusion that both of these loci are under non-neutral balancing selection; other regions of both genes appear to be under positive selection. Our data show that the het-c2/pin-c2 haplotype emerged by a recombination event between the het-c1/pin-c1 and het-c3/pin-c3 approximately 3–12 million years ago. These results support models by which loci that confer nonself discrimination form by the association of polymorphic genes with genes containing HET domains. Distinct allele classes can emerge by recombination and positive selection and are subsequently maintained by balancing selection and divergence of intergenic sequence resulting in recombination blocks between haplotypes.