Accession numbers for RNA-Seq datasets.

The Dothideomycete pathogen Coniothyrium glycines causes red leaf blotch of soybean, a major disease in Africa. It is one of two fungal plant pathogens on the USDA PPQ Select Agents and Toxins list of pathogens important to the biosecurity of the United States, reflective of its potential to be highly destructive if introduced. Despite its importance, there are no published reports regarding the molecular basis of host infection. Examination of the C. glycines genome revealed a secondary metabolite gene cluster that is similar in gene content and organization to clusters that synthesize light-activated perylenequinone toxins, such as cercosporin. Perylenequinones are non-host specific toxins that, upon exposure to light, generate reactive oxygen species, which have near-universal toxicity to plant hosts. Coniothyrium glycines isolates from eastern and southern Africa were cultured axenically under light and dark conditions. Light-grown cultures produced red-pink pigmentation typical of perylenequinones. Differential gene expression analysis showed that six of the eight genes in the biosynthetic gene cluster, including the polyketide synthase gene, were significantly upregulated in light. Liquid chromatography-mass spectrometry confirmed production of the perylenequinone elsinochrome A, a known virulence factor in other fungal pathogens. On leaves incubated in the dark, significantly fewer lesions formed and symptoms were delayed, compared to leaves incubated in the light. In addition, we identified orthologous gene clusters in more distantly related Dothideomycete plant pathogens where their presence was previously unknown, indicating a broader importance of these toxins to agriculture and fungal ecology. This work provides the first evidence that elsinochrome A may contribute to the virulence of C. glycines.

座囊菌纲（Dothideomycetes）病原菌大豆生盾壳霉（Coniothyrium glycines）可引发大豆红叶斑病，这是非洲地区的主要大豆病害之一。该病原菌是入选美国农业部动植物检疫局（USDA PPQ）精选病原体与毒素名录的两种重要植物病原真菌之一，该名录收录的病原体对美国生物安全具有重大意义，足见该病原菌一旦传入可造成极强的破坏性。尽管其具有如此重要的研究与应用价值，但目前尚无关于其宿主侵染分子机制的公开研究报道。对大豆生盾壳霉基因组的分析发现，其存在一个次级代谢产物基因簇，该基因簇的基因组成与结构与合成光活化苝醌类毒素（perylenequinone）的基因簇高度相似，例如尾孢菌素（cercosporin）合成基因簇。苝醌类毒素属于非寄主专化性毒素，在光照条件下可产生活性氧，对植物宿主具有近乎广谱的毒性。研究人员对采自东非与南非的大豆生盾壳霉分离株进行了明暗条件下的无菌培养。光照培养的菌株呈现出苝醌类毒素典型的红粉色色素沉着。差异基因表达分析结果显示，该生物合成基因簇的8个基因中有6个（包括聚酮合酶基因）在光照条件下显著上调表达。液相色谱-质谱联用（LC-MS）技术证实，该菌株可产生苝醌类化合物痂囊腔菌素A（elsinochrome A），该物质在其他植物病原真菌中已被证实为致病因子。与光照培养的叶片相比，暗培养的叶片上病斑形成数量显著更少，且病症出现时间延迟。此外，研究人员在亲缘关系更远的座囊菌纲植物病原真菌中发现了此前未被报道的同源基因簇，这表明这类毒素对农业生产与真菌生态学均具有更广泛的重要意义。本研究首次证实，痂囊腔菌素A可能参与大豆生盾壳霉的致病过程。