Kyoto University, Kyoto, Japan.
Mol Plant Microbe Interact. 2012 Dec;25(12):1552-61. doi: 10.1094/MPMI-05-12-0131-R.
Both Colletotrichum and Magnaporthe spp. develop appressoria pigmented with melanin, which is essential for fungal pathogenicity. 1,8-Dihydroxynaphthalene (1,8-DHN) is believed to be polymerized to yield melanin around the appresorial cell wall through the oxidative activity of laccases. However, no 1,8-DHN laccase has yet been identified in either Colletotrichum or Magnaporthe spp. Here, we report a laccase gene, LAC2, that is involved in the appressorial melanization of Colletotrichum orbiculare, which causes cucumber anthracnose. LAC2 encodes a protein with a signal peptide and has high homology to fungal laccases. The conidial color of lac2 mutants is distinct from that of the C. orbiculare wild type, and the mutants are nonpathogenic. Notably, the mutant appressoria are defective in melanization, and a host invasion assay showed that the appressoria are nonfunctional. LAC2 was induced during appressorial melanization. These results suggest that LAC2 oxidizes 1,8-DHN in the appressoria. The LAC2 homologues of other fungi located in the same phylogenetic clade as LAC2 fully complemented the lac2 mutants. Interestingly, a LAC2 homologue, located in a different clade, complemented the conidial pigmentation but not appressorial melanization of the mutants, suggesting that the LAC2 function in appressorial melanization might only be conserved in laccases of the LAC2 clade.
球腔菌属和稻瘟病菌属都能产生黑色素体着色的附着胞，黑色素体对于真菌的致病性至关重要。1,8-二羟基萘（1,8-DHN）被认为通过漆酶的氧化活性聚合，在附着胞细胞壁周围生成黑色素。然而，在球腔菌属或稻瘟病菌属中尚未鉴定出任何 1,8-DHN 漆酶。在这里，我们报告了一个与黄瓜炭疽病病原菌——炭疽菌属（Colletotrichum orbiculare）附着胞黑化有关的漆酶基因 LAC2。LAC2 编码一个带有信号肽的蛋白质，与真菌漆酶具有高度同源性。lac2 突变体的分生孢子颜色与 C. orbiculare 野生型明显不同，且突变体不具有致病性。值得注意的是，突变体的附着胞在黑化过程中存在缺陷，宿主入侵试验表明附着胞失去了功能。LAC2 在附着胞黑化过程中被诱导。这些结果表明，LAC2 氧化附着胞中的 1,8-DHN。与 LAC2 位于同一系统发育枝中的其他真菌的 LAC2 同源物完全弥补了 lac2 突变体的缺陷。有趣的是，位于不同枝中的 LAC2 同源物弥补了突变体的分生孢子颜色，但没有弥补附着胞的黑化，这表明 LAC2 在附着胞黑化中的功能可能仅在 LAC2 枝系的漆酶中保守。
