Milgroom Michael G, Jiménez-Gasco María del Mar, Olivares García Concepción, Drott Milton T, Jiménez-Díaz Rafael M
Department of Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, New York, United States of America.
Department of Plant Pathology and Environmental Microbiology, The Pennsylvania State University, University Park, Pennsylvania, United States of America.
PLoS One. 2014 Sep 2;9(9):e106740. doi: 10.1371/journal.pone.0106740. eCollection 2014.
Most asexual species of fungi have either lost sexuality recently, or they experience recombination by cryptic sexual reproduction. Verticillium dahliae is a plant-pathogenic, ascomycete fungus with no known sexual stage, even though related genera have well-described sexual reproduction. V. dahliae reproduces mitotically and its population structure is highly clonal. However, previously described discrepancies in phylogenetic relationships among clonal lineages may be explained more parsimoniously by recombination than mutation; therefore, we looked for evidence of recombination within and between clonal lineages. Genotyping by sequencing was performed on 141 V. dahliae isolates from diverse geographic and host origins, resulting in 26,748 single-nucleotide polymorphisms (SNPs). We found a strongly clonal population structure with the same lineages as described previously by vegetative compatibility groups (VCGs) and molecular markers. We detected 443 recombination events, evenly distributed throughout the genome. Most recombination events detected were between clonal lineages, with relatively few recombinant haplotypes detected within lineages. The only three isolates with mating type MAT1-1 had recombinant SNP haplotypes; all other isolates had mating type MAT1-2. We found homologs of eight meiosis-specific genes in the V. dahliae genome, all with conserved or partially conserved protein domains. The extent of recombination and molecular signs of sex in (mating-type and meiosis-specific genes) suggest that V. dahliae clonal lineages arose by recombination, even though the current population structure is markedly clonal. Moreover, the detection of new lineages may be evidence that sexual reproduction has occurred recently and may potentially occur under some circumstances. We speculate that the current clonal population structure, despite the sexual origin of lineages, has arisen, in part, as a consequence of agriculture and selection for adaptation to agricultural cropping systems.
大多数无性繁殖的真菌物种要么最近失去了有性生殖能力，要么通过隐秘的有性生殖进行重组。大丽轮枝菌是一种植物病原性子囊菌，尽管相关属具有详细描述的有性生殖过程，但它却没有已知的有性阶段。大丽轮枝菌进行有丝分裂繁殖，其种群结构高度克隆。然而，先前描述的克隆谱系之间系统发育关系的差异，用重组来解释可能比用突变更为简约；因此，我们寻找克隆谱系内部和之间重组的证据。对来自不同地理和宿主来源的141株大丽轮枝菌分离株进行测序基因分型，产生了26748个单核苷酸多态性（SNP）。我们发现了一个与先前通过营养体亲和群（VCG）和分子标记描述的相同谱系的强克隆种群结构。我们检测到443次重组事件，均匀分布在整个基因组中。检测到的大多数重组事件发生在克隆谱系之间，谱系内检测到的重组单倍型相对较少。仅有的三个具有交配型MAT1-1的分离株具有重组SNP单倍型；所有其他分离株具有交配型MAT1-2。我们在大丽轮枝菌基因组中发现了八个减数分裂特异性基因的同源物，它们都具有保守或部分保守的蛋白质结构域。重组程度和性的分子迹象（交配型和减数分裂特异性基因）表明，尽管当前种群结构明显是克隆性的，但大丽轮枝菌的克隆谱系是通过重组产生的。此外，新谱系的检测可能是有性生殖最近发生且可能在某些情况下潜在发生的证据。我们推测，尽管谱系有性起源，但当前的克隆种群结构部分是由于农业以及对适应农业种植系统的选择而产生的。
