Zhang Qiong, Berkey Robert, Pan Zhiyong, Wang Wenming, Zhang Yi, Ma Xianfeng, King Harlan, Xiao Shunyuan
a Institute for Bioscience and Biotechnology Research ; University of Maryland ; Rockville , MD USA.
Plant Signal Behav. 2015;10(3):e989766. doi: 10.4161/15592324.2014.989766.
Powdery mildew fungi form feeding structures called haustoria inside epidermal cells of host plants to extract photosynthates for their epiphytic growth and reproduction. The haustorium is encased by an interfacial membrane termed the extrahaustorial membrane (EHM). The atypical resistance protein RPW8.2 from Arabidopsis is specifically targeted to the EHM where RPW8.2 activates haustorium-targeted (thus broad-spectrum) resistance against powdery mildew fungi. EHM-specific localization of RPW8.2 suggests the existence of an EHM-oriented protein/membrane trafficking pathway during EHM biogenesis. However, the importance of this specific trafficking pathway for host defense has not been evaluated via a genetic approach without affecting other trafficking pathways. Here, we report that expression of EHM-oriented, nonfunctional RPW8.2 chimeric proteins exerts dominant negative effect over functional RPW8.2 and potentially over other EHM-localized defense proteins, thereby compromising both RPW8.2-mediated and basal resistance to powdery mildew. Thus, our results highlight the importance of the EHM-oriented protein/membrane trafficking pathway for host resistance against haustorium-forming pathogens such as powdery mildew fungi.
白粉菌在寄主植物的表皮细胞内形成称为吸器的取食结构，以获取光合产物用于其体表生长和繁殖。吸器被一层称为吸器外膜（EHM）的界面膜包裹。拟南芥中的非典型抗性蛋白RPW8.2特异性定位于EHM，在那里RPW8.2激活针对吸器的（即广谱的）对白粉菌的抗性。RPW8.2在EHM上的特异性定位表明在EHM生物合成过程中存在一条以EHM为导向的蛋白质/膜运输途径。然而，这种特定运输途径对寄主防御的重要性尚未通过不影响其他运输途径的遗传方法进行评估。在此，我们报道以EHM为导向的无功能RPW8.2嵌合蛋白的表达对功能性RPW8.2以及可能对其他定位于EHM的防御蛋白发挥显性负效应，从而损害RPW8.2介导的和对白粉病的基础抗性。因此，我们的结果突出了以EHM为导向的蛋白质/膜运输途径对寄主抵抗形成吸器的病原体（如白粉菌）的重要性。
