Tsuji Gento, Fujii Satoshi, Tsuge Seiji, Shiraishi Tomonori, Kubo Yasuyuki
Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto Prefectural University, Kyoto 606-8522, Japan.
Mol Plant Microbe Interact. 2003 Apr;16(4):315-25. doi: 10.1094/MPMI.2003.16.4.315.
Colletotrichum lagenarium is the causal agent of anthracnose of cucumber. This fungus produces a darkly melanized infection structure, appressoria, to penetrate the host leaves. The C. lagenarium CMK1 gene, a homologue of the Saccharomyces cerevisiae FUS3/KSS1 mitogen-activated protein (MAP) kinase genes, was shown to regulate conidial germination, appressorium formation, and invasive growth. In S. cerevisiae, Ste12p is known to be a transcriptional factor downstream of Fus3p/Kss1p MAP kinases. To evaluate the CMK1 MAP kinase pathway, we isolated the Ste12 homologue CST1 gene from C. lagenarium and characterized. The cst1delta strains were nonpathogenic on intact host leaves, but could form lesions when inoculated on wounded leaves. Conidia of the cst1delta strains could germinate and form melanized appressoria on both host leaf surface and artificial cellulose membrane, but could not produce infectious hyphae from appressoria, suggesting that CST1 is essential for appressorium penetration in C. lagenarium. In addition, matured appressoria of the cst1delta strains contained an extremely low level of lipid droplets compared with that of the wild-type strain. Lipid droplets were abundant in conidia of the cst1delta strains, but rapidly disappeared during appressorium formation. This misscheduled lipid degradation might be related to the failure of appressorium penetration in the cst1delta strain.
葫芦炭疽菌是黄瓜炭疽病的病原菌。这种真菌会产生一种深色黑化的侵染结构——附着胞，用于穿透寄主叶片。葫芦炭疽菌CMK1基因是酿酒酵母FUS3/KSS1丝裂原活化蛋白（MAP）激酶基因的同源物，已证明其可调控分生孢子萌发、附着胞形成和侵入性生长。在酿酒酵母中，Ste12p是已知的Fus3p/Kss1p MAP激酶下游的转录因子。为了评估CMK1 MAP激酶途径，我们从葫芦炭疽菌中分离出Ste12同源物CST1基因并进行了表征。cst1delta突变体菌株在完整的寄主叶片上无致病性，但接种在受伤叶片上时会形成病斑。cst1delta突变体菌株的分生孢子能够在寄主叶片表面和人工纤维素膜上萌发并形成黑化的附着胞，但不能从附着胞产生侵染性菌丝，这表明CST1对于葫芦炭疽菌附着胞的穿透至关重要。此外，与野生型菌株相比，cst1delta突变体菌株成熟的附着胞中脂质滴水平极低。cst1delta突变体菌株的分生孢子中脂质滴丰富，但在附着胞形成过程中迅速消失。这种错误安排的脂质降解可能与cst1delta突变体菌株附着胞穿透失败有关。
