A fungal effector promotes infection via stabilizing a negative regulatory factor of chloroplast immunity
Kunqin Xiao, Feng Yang, Wenjing Cui, Anmo Li, Jeffrey A. Rollins, Jinxin Guo, Xinhua Sun, Fengting Wang, Xiaojie Wang, Xun Xu, Yanhua Zhang, Xianghui Zhang, Jinliang Liu, Hongyu Pan
Abstract
Chloroplasts are crucial players in immunity and photosynthesis. However, how chloroplasts arrange the transition between photosynthesis and immunity and how pathogens manipulate this transition remains elusive. Here we report an effector SsCm1 from Sclerotinia sclerotiorum, one of devastating phytopathogenic fungi, inhibits chloroplast immunity and resistance to pathogens, and alleviates photoinhibition in immune state. This is accomplished through stabilizing the conserved chloroplast protein MORF2, which is degraded during immunization and is a suppressor of photoinhibition, cell death, and chloroplast immunity. Overexpression of SsCm1 or MORF2 in plants represses basic immunity and resistance to pathogens, whereas deletion of SsCm1 reduces S. sclerotiorum virulence. Notably, SsCm1 possesses no chorismate mutase activity, which is different from the previously reported Cm effectors. This work reveals a strategy to fine-tune growth-defense balance in chloroplasts by manipulating MORF2, and a pathogenic strategy to subvert the process and promote infection via enzymatically nonfunctional effector stabilizing MORF2. The SsCm1 effector of the pathogenic fungus Sclerotinia sclerotiorum, despite the lack of canonical chorismate mutase activity, inhibits chloroplast immunity and alleviates photoinhibition in host cells via stabilizing chloroplast protein MORF2.