Department of Biology, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada.
Key Laboratory of Biology and Genetic Improvement of Oil Crops, Ministry of Agriculture, Oil Crops Research Institute, Chinese Academy of Agricultural Sciences, Wuhan, Hubei 430062, China.
Plant Cell. 2021 Sep 24;33(9):3151-3175. doi: 10.1093/plcell/koab170.
The actin cytoskeleton regulates an array of diverse cellular activities that support the establishment of plant-microbe interactions and plays a critical role in the execution of plant immunity. However, molecular and cellular mechanisms regulating the assembly and rearrangement of actin filaments (AFs) at plant-pathogen interaction sites remain largely elusive. Here, using live-cell imaging, we show that one of the earliest cellular responses in Arabidopsis thaliana upon powdery mildew attack is the formation of patch-like AF structures beneath fungal invasion sites. The AFs constituting actin patches undergo rapid turnover, which is regulated by the actin-related protein (ARP)2/3 complex and its activator, the WAVE/SCAR regulatory complex (W/SRC). The focal accumulation of phosphatidylinositol-4,5-bisphosphate at fungal penetration sites appears to be a crucial upstream modulator of the W/SRC-ARP2/3 pathway-mediated actin patch formation. Knockout of W/SRC-ARP2/3 pathway subunits partially compromised penetration resistance with impaired endocytic recycling of the defense-associated t-SNARE protein PEN1 and its deposition into apoplastic papillae. Simultaneously knocking out ARP3 and knocking down the Class I formin (AtFH1) abolished actin patch formation, severely impaired the deposition of cell wall appositions, and promoted powdery mildew entry into host cells. Our results demonstrate that the ARP2/3 complex and formins, two actin-nucleating systems, act cooperatively and contribute to Arabidopsis penetration resistance to fungal invasion.
肌动蛋白细胞骨架调节着一系列多样化的细胞活动，这些活动支持植物与微生物相互作用的建立，并在植物免疫的执行中发挥关键作用。然而，调节植物-病原体相互作用部位肌动蛋白丝（AFs）组装和重排的分子和细胞机制在很大程度上仍未被揭示。在这里，我们使用活细胞成像技术表明，在拟南芥受到白粉病攻击后，最早的细胞反应之一是在真菌入侵部位下方形成斑片状 AF 结构。构成肌动蛋白斑的 AF 经历快速周转，这由肌动蛋白相关蛋白（ARP）2/3 复合物及其激活剂 WAVE/SCAR 调节复合物（W/SRC）调节。在真菌穿透部位，磷脂酰肌醇-4,5-二磷酸的局域聚集似乎是 W/SRC-ARP2/3 途径介导肌动蛋白斑形成的关键上游调节剂。W/SRC-ARP2/3 途径亚基的敲除部分削弱了穿透抗性，同时 PEN1 防御相关 t-SNARE 蛋白的内吞回收受损，并且不能沉积到质外体乳突中。同时敲除 ARP3 和下调 I 类成纤维细胞（AtFH1）会破坏肌动蛋白斑的形成，严重损害细胞壁附着的沉积，并促进白粉病进入宿主细胞。我们的结果表明，ARP2/3 复合物和形成素这两种肌动蛋白成核系统协同作用，有助于拟南芥对真菌入侵的穿透抗性。
