Structural variation and phylogenetic analysis of the mating-type locus in the genus <i>Morchella</i>

True morels (Morchella spp.) are a group of edible fungi that are in high demand worldwide. However, this group of fungi remains poorly understood in terms of its genetic structure, life cycle, and mating system. In the present study, we cloned the MAT locus in Morchella sp. Mes-20 using long-range polymerase chain reaction (PCR) amplification. Our results showed that the MAT1-2 idiomorph in the single-ascospore isolate YAASMCB-3 was 7.5 kb in length, harboring a single MAT1-2-1 gene, whereas the MAT1-1 idiomorph in the isolate YAASMCB-15 was 7.8 kb, carrying both MAT1-1-1 and MAT1-1-10 genes. Mating-type diagnostic assays of single-ascospore populations confirmed that Mes-20 is heterothallic. In addition, 42 collections belonging to 17 morel species (7 black morel species [Elata clade], 9 yellow morel species [Esculenta clade], and 1 species from the Rufobrunnea clade) were used to clone and characterize the MAT1-1-1 and MAT1-2-1 genes for development of the mating gene genealogies. In concordance with the multilocus phylogenetic trees, collections for the respective species were readily distinguished by well-supported lineages in mating gene genealogies. The topologies were consistent within the Elata clade, whereas the branching order and sister-group relationships slightly varied within the Esculenta clade. Our results show that species in the genus Morchella could be delimited by mating gene genealogies.羊肚菌属（Morchella spp.）真菌是一类全球市场需求旺盛的食用真菌。然而，目前学界对该类真菌的遗传结构、生活史及交配系统仍知之甚少。本研究利用长距离聚合酶链式反应（long-range polymerase chain reaction，PCR）扩增技术，克隆了羊肚菌菌株Mes-20的交配型基因座（MAT locus）。结果显示，单孢子分离菌株YAASMCB-3的MAT1-2型异形基因座（idiomorph）长度为7.5 kb，仅携带MAT1-2-1基因；而分离菌株YAASMCB-15的MAT1-1型异形基因座长度为7.8 kb，同时携带有MAT1-1-1与MAT1-1-10两个基因。针对单孢子群体的交配型鉴定实验证实，菌株Mes-20为异宗配合类型。此外，本研究纳入17个羊肚菌物种的42份标本（其中7个隶属于黑羊肚菌分支（Elata clade）、9个隶属于黄羊肚菌分支（Esculenta clade），另有1份属于Rufobrunnea分支），通过克隆并鉴定MAT1-1-1与MAT1-2-1基因，构建了交配基因谱系树。与多位点系统发育树的结果一致，交配基因谱系树可通过高支持度的演化支清晰区分各对应物种。黑羊肚菌分支内部的拓扑结构完全一致，而黄羊肚菌分支内部的分支顺序与姊妹群关系则存在小幅差异。本研究结果证实，可通过交配基因谱系树对羊肚菌属物种进行物种界定。