Xin Xiu-Fang, Nomura Kinya, Aung Kyaw, Velásquez André C, Yao Jian, Boutrot Freddy, Chang Jeff H, Zipfel Cyril, He Sheng Yang
Department of Energy, Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
Howard Hughes Medical Institute-Gordon and Betty Moore Foundation, Michigan State University, East Lansing, Michigan 48824, USA.
Nature. 2016 Nov 24;539(7630):524-529. doi: 10.1038/nature20166.
High humidity has a strong influence on the development of numerous diseases affecting the above-ground parts of plants (the phyllosphere) in crop fields and natural ecosystems, but the molecular basis of this humidity effect is not understood. Previous studies have emphasized immune suppression as a key step in bacterial pathogenesis. Here we show that humidity-dependent, pathogen-driven establishment of an aqueous intercellular space (apoplast) is another important step in bacterial infection of the phyllosphere. Bacterial effectors, such as Pseudomonas syringae HopM1, induce establishment of the aqueous apoplast and are sufficient to transform non-pathogenic P. syringae strains into virulent pathogens in immunodeficient Arabidopsis thaliana under high humidity. Arabidopsis quadruple mutants simultaneously defective in a host target (AtMIN7) of HopM1 and in pattern-triggered immunity could not only be used to reconstitute the basic features of bacterial infection, but also exhibited humidity-dependent dyshomeostasis of the endophytic commensal bacterial community in the phyllosphere. These results highlight a new conceptual framework for understanding diverse phyllosphere-bacterial interactions.
高湿度对影响农田和自然生态系统中植物地上部分（叶际）的多种病害发展具有强烈影响，但这种湿度效应的分子基础尚不清楚。先前的研究强调免疫抑制是细菌致病的关键步骤。在此我们表明，湿度依赖性、病原体驱动的细胞间水相空间（质外体）的形成是叶际细菌感染的另一个重要步骤。细菌效应蛋白，如丁香假单胞菌HopM1，可诱导水性质外体的形成，并且足以在高湿度条件下将无致病性的丁香假单胞菌菌株转化为免疫缺陷型拟南芥中的致病病原体。在HopM1的宿主靶点（AtMIN7）和模式触发免疫方面同时存在缺陷的拟南芥四重突变体，不仅可用于重构细菌感染的基本特征，还表现出叶际内生共生细菌群落的湿度依赖性动态失衡。这些结果突出了一个理解多种叶际-细菌相互作用的新概念框架。
