1 Department of Plant and Soil Sciences, Forestry and Agricultural Biotechnology Institute (FABI), Genomics Research Institute, University of Pretoria, Private Bag x20, Hatfield 0028, South Africa.
2 Department of Plant Pathology, University of Arkansas, Fayetteville, AR 72701, U.S.A.; and.
Mol Plant Microbe Interact. 2017 Sep;30(9):710-724. doi: 10.1094/MPMI-03-17-0054-R. Epub 2017 Jul 7.
Gray leaf spot (GLS), caused by the sibling species Cercospora zeina or Cercospora zeae-maydis, is cited as one of the most important diseases threatening global maize production. C. zeina fails to produce cercosporin in vitro and, in most cases, causes large coalescing lesions during maize infection, a symptom generally absent from cercosporin-deficient mutants in other Cercospora spp. Here, we describe the C. zeina cercosporin toxin biosynthetic (CTB) gene cluster. The oxidoreductase gene CTB7 contained several insertions and deletions as compared with the C. zeae-maydis ortholog. We set out to determine whether complementing the defective CTB7 gene with the full-length gene from C. zeae-maydis could confer in vitro cercosporin production. C. zeina transformants containing C. zeae-maydis CTB7 were generated by Agrobacterium tumefaciens-mediated transformation and were evaluated for in vitro cercosporin production. When grown on nitrogen-limited medium in the light-conditions conducive to cercosporin production in other Cercospora spp.-one transformant accumulated a red pigment that was confirmed to be cercosporin by the KOH assay, thin-layer chromatography, and ultra performance liquid chromatography-quadrupole-time-of-flight mass spectrometry. Our results indicated that C. zeina has a defective CTB7, but all other necessary machinery required for synthesizing cercosporin-like molecules and, thus, C. zeina may produce a structural variant of cercosporin during maize infection.
灰斑病（GLS）由姊妹种玉米尾孢菌或玉米叶斑病菌引起，被认为是威胁全球玉米生产的最重要疾病之一。玉米尾孢菌在体外无法产生尾孢菌素，而且在大多数情况下，会导致玉米感染时出现大的融合性病变，而其他尾孢菌属中的尾孢菌素缺陷突变体通常没有这种症状。在这里，我们描述了玉米尾孢菌的尾孢菌素毒素生物合成（CTB）基因簇。与玉米叶斑病菌的同源物相比，氧化还原酶基因 CTB7 有几个插入和缺失。我们着手确定用玉米叶斑病菌的全长基因来补充有缺陷的 CTB7 基因是否能在体外产生尾孢菌素。通过农杆菌介导的转化生成了含有玉米叶斑病菌 CTB7 的玉米尾孢菌转化体，并对其进行了体外尾孢菌素生产评估。当在氮限制培养基中、在有利于其他尾孢菌属产生尾孢菌素的光照条件下生长时，一个转化体积累了一种红色色素，该色素通过 KOH 测定、薄层层析和超高效液相色谱-四极杆飞行时间质谱法确认为尾孢菌素。我们的结果表明，玉米尾孢菌有一个缺陷的 CTB7，但合成类似尾孢菌素的分子所需的所有其他必要机制都存在，因此，玉米尾孢菌在感染玉米时可能会产生尾孢菌素的结构变体。
