Sexual reproduction is ubiquitous in nature, and nowhere is this more so than in the fungi. Heterothallic behaviour is observed when there is a strict requirement of contact between two individuals of opposite mating type for sexual reproduction to occur. In contrast, a homothallic species can complete the entire sexual cycle in isolation, although several genetic mechanisms underpin this self-fertility. These can be inferred by characterising the structure and gene-content of the mating-type locus, which contains genes that are involved in the regulation of sexual reproduction. In this study, the genetic basis of homothallism in Thielaviopsis cerberus was investigated, the only known self-fertile species within this genus. Using genome sequencing and conventional molecular techniques, two versions of the mating-type locus were identified in this species. This is typical of species that have a unidirectional mating-type switching reproductive strategy. The first version was a self-fertile locus that contained four known mating-type genes, while the second was a self-sterile version with a single mating-type gene. The conversion from a self-fertile to a self-sterile locus is likely mediated by a homologous recombination event at two direct repeats present in the self-fertile locus, resulting in the deletion of three mating-type genes and one of the repeats. Both locus versions were present in isolates that were self-fertile, while self-sterility was caused by the presence of only a switched locus. This study provides a clear example of the architectural fluidity in the mating-type loci that is common among even closely related fungal species.

有性繁殖在自然界中无处不在，在真菌中尤为如此。当严格要求两个相反交配类型的个体接触以进行有性繁殖时，就会观察到异种行为。相比之下，同族物种可以独立完成整个性周期，尽管有几种遗传机制支持这种自我生育。这些可以通过表征交配型基因座的结构和基因含量来推断，其中包含参与调节有性生殖的基因。在这项研究中，Thielaviopsis cerberus同源性的遗传基础进行了调查，这是该属中唯一已知的自育物种。使用基因组测序和常规分子技术，在该物种中鉴定了两种版本的交配型基因座。这是具有单向交配型转换繁殖策略的物种的典型特征。第一个版本是包含四个已知交配型基因的自育基因座，而第二个版本是具有单个交配型基因的自不育版本。从自体可育基因座到自体不育基因座的转化可能是由自体基因座中存在的两个直接重复处的同源重组事件介导的，导致三个交配型基因和一个重复序列的缺失。两个基因座版本都存在于可自我繁殖的分离株中，而自我不育是由仅存在转换位点引起的。这项研究提供了一个清晰的例子，说明即使在密切相关的真菌物种中也很常见的交配型基因座中的结构流动性。