PLoS Pathogens:中科院微生物所郭惠珊课题组发表大丽轮枝菌侵染过

2017年3月10日，国际微生物学知名期刊《PLOS Pathogens》在线发表了中国科学院微生物研究所研究员郭惠珊课题组题为“Secretory proteins are delivered to the septin-organized penetration interface during root infection by Verticillium dahliae”的研究论文，研究论文报道了大丽轮枝菌侵染过程。博士研究生周婷婷为论文的第一作者，郭惠珊为通讯作者。

大丽轮枝菌是一种土传病原真菌，通过形成附着枝感染植物根部，在世界范围内引起严重的黄萎病害，对我国棉花生产造成巨大的经济损失。和其他病原微生物一样，大丽轮枝菌的重要致病策略之一是分泌效应蛋白到植物细胞，干扰植物免疫反应;但其分泌结构和分泌转运机制亟待探究。

郭惠珊课题组在前期发现大丽轮枝菌侵染结构附着枝的基础上，继续开展了大丽轮枝菌侵染过程中分泌蛋白传递途径的研究。课题组发现大丽轮枝菌通过反复形成附着枝和穿透钉以刺穿植物根细胞壁，当形成入侵菌丝后，穿透钉衍化成菌丝颈环(图A)，并与寄主形成紧密互作的穿透界面。课题组通过细胞生物学研究发现大丽轮枝菌细胞骨架组分Septin5和F-actin以成环的形式(Septin环)定位于菌丝颈环，分泌蛋白在此处大量分泌至Septin环之外(图B);分泌蛋白在穿透界面的有效分泌依赖于Septin5在菌丝颈环的有序组织。进一步实验表明囊泡转运因子VdSec22、VdSyn8和胞吐体亚基VdExo70参与分泌蛋白的传递和转运，其缺失均导致分泌蛋白滞留在附着枝及菌丝颈环之内;VdSep5，VdSec22，VdSyn8及VdExo70基因的敲除突变体会显著地降低大丽轮枝菌在棉花上的致病性。

研究首次阐明了大丽轮枝菌依赖Septin5的分泌蛋白转运机制，即Septin5骨架蛋白在菌丝颈环组装并形成了真菌-寄主的穿透界面，可以高效分泌效应蛋白;该研究揭示了大丽轮枝菌的附着枝既是侵染结构又是独特的分泌结构，是大丽轮枝菌成功侵染植物的关键信号中枢。

原文链接：

Secretory proteins are delivered to the septin-organized penetration interfAce during root infection by Verticillium dahliae

原文摘要：

Successful infection of the host requires secretion of effector proteins to evade or suppress plant immunity. Secretion of effectors in root-infecting fungal pathogens, however, remains unexplored. We previously reported that Verticillium dahliae, a root-infecting phytopathogenic fungus, develops a penetration peg from a hyphopodium to infect cotton roots. In this study, we report that a septin ring, requiring VdSep5, partitions the hyphopodium and the invasive hypha and form the specialized fungus-host interface. The mutant strain, VdΔnoxb, in which NADPH oxidase B (VdNoxB) is deleted, impaired formation of the septin ring at the hyphal neck, indicating that NADPH oxidases regulate septin ring organization. Using GFP tagging and live cell imaging, we observed that several signal peptide containing secreted proteins showed ring signal accumulation/secretion at the penetration interface surrounding the hyphal neck. Targeted mutation for VdSep5 reduced the delivery rate of secretory proteins to the penetration interface. Blocking the secretory pathway by disrupting the vesicular trafficking factors,VdSec22 and VdSyn8, or the exocyst subunit, VdExo70, also arrested delivery of the secreted proteins inside the hyphopodium. Reduced virulence was observed when cotton roots were infected with VdΔsep5, VdΔsec22, VdΔsyn8 and VdΔexo70 mutants compared to infection with the isogenic wild-type V592. Taken together, our data demonstrate that the hyphal neck is an important site for protein secretion during plant root infection, and that the multiple secretory routes are involved in the secretion.

doi:10.1371/journal.ppat.1006275

作者：郭惠珊