Chen Jisheng, Zheng Wu, Zheng Shiqin, Zhang Dongmei, Sang Weijian, Chen Xiao, Li Guangpu, Lu Guodong, Wang Zonghua
Key Laboratory of Biopesticide and Chemistry Biology, Ministry of Education, Fujian Agriculture and Forestry University, Fuzhou, China.
PLoS Pathog. 2008 Nov;4(11):e1000202. doi: 10.1371/journal.ppat.1000202. Epub 2008 Nov 14.
Rac1 is a small GTPase involved in actin cytoskeleton organization and polarized cell growth in many organisms. In this study, we investigate the biological function of MgRac1, a Rac1 homolog in Magnaporthe grisea. The MgRac1 deletion mutants are defective in conidial production. Among the few conidia generated, they are malformed and defective in appressorial formation and consequently lose pathogenicity. Genetic complementation with native MgRac1 fully recovers all these defective phenotypes. Consistently, expression of a dominant negative allele of MgRac1 exhibits the same defect as the deletion mutants, while expression of a constitutively active allele of MgRac1 can induce abnormally large conidia with defects in infection-related growth. Furthermore, we show the interactions between MgRac1 and its effectors, including the PAK kinase Chm1 and NADPH oxidases (Nox1 and Nox2), by the yeast two-hybrid assay. While the Nox proteins are important for pathogenicity, the MgRac1-Chm1 interaction is responsible for conidiogenesis. A constitutively active Chm1 mutant, in which the Rac1-binding PBD domain is removed, fully restores conidiation of the MgRac1 deletion mutants, but these conidia do not develop appressoria normally and are not pathogenic to rice plants. Our data suggest that the MgRac1-Chm1 pathway is responsible for conidiogenesis, but additional pathways, including the Nox pathway, are necessary for appressorial formation and pathogenicity.
Rac1是一种小GTP酶，参与许多生物体中的肌动蛋白细胞骨架组织和极化细胞生长。在本研究中，我们研究了稻瘟病菌中Rac1同源物MgRac1的生物学功能。MgRac1缺失突变体在分生孢子产生方面存在缺陷。在产生的少数分生孢子中，它们畸形且附着胞形成有缺陷，因此失去致病性。用天然MgRac1进行遗传互补可完全恢复所有这些缺陷表型。一致地，MgRac1显性负等位基因的表达表现出与缺失突变体相同的缺陷，而MgRac1组成型活性等位基因的表达可诱导出异常大的分生孢子，且在与感染相关的生长方面存在缺陷。此外，我们通过酵母双杂交试验展示了MgRac1与其效应器之间的相互作用，包括PAK激酶Chm1和NADPH氧化酶（Nox1和Nox2）。虽然Nox蛋白对致病性很重要，但MgRac1 - Chm1相互作用负责分生孢子形成。一种组成型活性Chm1突变体，其中Rac1结合PBD结构域被去除，可完全恢复MgRac1缺失突变体的分生孢子形成，但这些分生孢子不能正常发育附着胞，并且对水稻植株无致病性。我们的数据表明，MgRac1 - Chm1途径负责分生孢子形成，但包括Nox途径在内的其他途径对于附着胞形成和致病性是必需的。
