NWAFU-PU Joint Research Center, State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi, 712100, China.
Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, 47907, USA.
Mol Plant Pathol. 2018 Feb;19(2):328-340. doi: 10.1111/mpp.12523. Epub 2017 Feb 10.
As a typical foliar pathogen, appressorium formation and penetration are critical steps in the infection cycle of Magnaporthe oryzae. Because appressorium formation and penetration are closely co-regulated with the cell cycle, and Cdc14 phosphatases have an antagonistic relationship with cyclin-dependent kinases (CDKs) on proteins related to mitotic exit and cytokinesis, in this study, we functionally characterized the MoCDC14 gene in M. oryzae. The Mocdc14 deletion mutant showed significantly reduced growth rate and conidiation. It was also defective in septum formation and nuclear distribution. Septation was irregular in Mocdc14 hyphae and hyphal compartments became multi-nucleate. Mutant conidia often showed incomplete septa or lacked any septum. During appressorium formation, the septum delimiting appressoria from the rest of the germ tubes was often formed far away from the neck of the appressoria or not formed at all. Unlike the wild-type, some mutant appressoria had more than one nucleus at 24 h. In addition to appressoria, melanization occurred on parts of the germ tubes and conidia, depending on the irregular position of the appressorium-delimiting septum. The Mocdc14 mutant was also defective in glycogen degradation during appressorium formation and appressorial penetration of intact plant cells. Similar defects in septum formation, melanization and penetration were observed with appressorium-like structures formed at hyphal tips in the Mocdc14 mutant. Often a long fragment of mutant hyphae was melanized, together with the apical appressorium-like structures. These results indicate that MoCDC14 plays a critical role in septation, nuclear distribution and pathogenesis in M. oryzae, and correct septum formation during conidiogenesis and appressorium formation requires the MoCdc14 phosphatase.
作为一种典型的叶病原菌，附着胞的形成和穿透是稻瘟病菌感染周期中的关键步骤。由于附着胞的形成和穿透与细胞周期密切相关，而且 Cdc14 磷酸酶与有丝分裂退出和胞质分裂相关的蛋白质上的细胞周期依赖性激酶（CDKs）呈拮抗关系，因此，在本研究中，我们对稻瘟病菌中的 MoCDC14 基因进行了功能表征。Mocdc14 缺失突变体的生长速度和产孢能力明显降低。它在隔膜形成和核分布方面也存在缺陷。Mocdc14 菌丝的隔膜形成不规则，菌丝隔室变成多核。突变体分生孢子经常表现出不完全的隔膜或缺乏任何隔膜。在附着胞形成过程中，将附着胞与剩余的芽管分隔开的隔膜常常远离附着胞的颈部形成，或者根本不形成。与野生型不同的是，一些突变体附着胞在 24 小时时有一个以上的核。除了附着胞之外，在芽管和分生孢子的部分部位还发生了黑色素沉着，这取决于附着胞分隔隔膜的不规则位置。Mocdc14 突变体在附着胞形成和完整植物细胞的附着胞穿透过程中也不能降解糖原。在 Mocdc14 突变体中，在菌丝顶端形成的类似附着胞的结构中观察到类似的隔膜形成、黑色素沉着和穿透缺陷。通常，突变体菌丝的长片段被黑色素化，与顶端类似附着胞的结构一起。这些结果表明，MoCDC14 在稻瘟病菌的隔膜形成、核分布和致病性中发挥着关键作用，并且正确的隔膜形成是分生孢子发生和附着胞形成所必需的，需要 MoCdc14 磷酸酶。
