Department of Plant Pathology, University of California Davis, Davis, California, United States of America.
PLoS One. 2013;8(2):e56895. doi: 10.1371/journal.pone.0056895. Epub 2013 Feb 15.
Sclerotinia sclerotiorum is a fungal plant pathogen and the causal agent of lettuce drop, an economically important disease of California lettuce. The structure of the S. sclerotiorum mating type locus MAT has previously been reported and consists of two idiomorphs that are fused end-to-end as in other homothallics. We investigated the diversity of S. sclerotiorum MAT using a total of 283 isolates from multiple hosts and locations, and identified a novel MAT allele that differed by a 3.6-kb inversion and was designated Inv+, as opposed to the previously known S. sclerotiorum MAT that lacked the inversion and was Inv-. The inversion affected three of the four MAT genes: MAT1-2-1 and MAT1-2-4 were inverted and MAT1-1-1 was truncated at the 3'-end. Expression of MAT genes differed between Inv+ and Inv- isolates. In Inv+ isolates, only one of the three MAT1-2-1 transcript variants of Inv- isolates was detected, and the alpha1 domain of Inv+ MAT1-1-1 transcripts was truncated. Both Inv- and Inv+ isolates were self-fertile, and the inversion segregated in a 1∶1 ratio regardless of whether the parent was Inv- or Inv+. This suggested the involvement of a highly regulated process in maintaining equal proportions of Inv- and Inv+, likely associated with the sexual state. The MAT inversion region, defined as the 3.6-kb MAT inversion in Inv+ isolates and the homologous region of Inv- isolates, was flanked by a 250-bp inverted repeat on either side. The 250-bp inverted repeat was a partial MAT1-1-1 that through mediation of loop formation and crossing over, may be involved in the inversion process. Inv+ isolates were widespread, and in California and Nebraska constituted half of the isolates examined. We speculate that a similar inversion region may be involved in mating type switching in the filamentous ascomycetes Chromocrea spinulosa, Sclerotinia trifoliorum and in certain Ceratocystis species.
核盘菌是一种真菌植物病原体，也是加利福尼亚生菜的重要经济作物菌核病的病原体。先前已经报道了核盘菌交配型位点 MAT 的结构，它由两个形态相同的部分组成，与其他同宗配合的真菌一样，它们首尾融合在一起。我们使用来自多个宿主和地点的总共 283 个分离株来研究核盘菌 MAT 的多样性，并鉴定了一种新的 MAT 等位基因，该基因通过 3.6kb 的倒位而不同，被指定为 Inv+，而之前已知的缺乏倒位的核盘菌 MAT 被指定为 Inv-。该倒位影响了四个 MAT 基因中的三个：MAT1-2-1 和 MAT1-2-4 发生了倒位，MAT1-1-1 在 3'-末端被截断。Inv+和 Inv-分离株的 MAT 基因表达不同。在 Inv+分离株中，只检测到 Inv-分离株三个 MAT1-2-1 转录变体中的一个，并且 Inv+MAT1-1-1 转录本的 alpha1 结构域被截断。Inv-和 Inv+分离株都是自育的，无论亲本是 Inv-还是 Inv+，该倒位都以 1∶1 的比例分离。这表明在维持 Inv-和 Inv+的比例方面涉及到一个高度调控的过程，这可能与性状态有关。MAT 倒位区被定义为 Inv+分离株中的 3.6kb MAT 倒位和 Inv-分离株中的同源区，在两侧侧翼是 250bp 的反向重复序列。250bp 的反向重复序列是部分 MAT1-1-1，通过环形成和交叉作用的介导，可能参与倒位过程。Inv+分离株分布广泛，在加利福尼亚和内布拉斯加州，它们构成了所检查的分离株的一半。我们推测，类似的倒位区可能涉及丝状子囊菌 Chromocrea spinulosa、核盘菌 trifoliorum 和某些 Ceratocystis 物种的交配型转换。
