Abstract
Production of superoxide anion and nitric oxide in plant immune and stress responses is called as radical burst for its rapid induction. It has been identified that MAPK cascade plays a pivotal role in the induction of radical burst. On the other hand, we found that chloroplasts-localized CAS protein is also involved with the radical burst. Arabidopsis CAS knock-out mutant (cas-1) shows delay of HR cell death and the reduction of radical productions against the infection of avirulence Pseudomonas syringae pv. tomato DC3000 (avrRpt2). Furthermore, CAS is involved with flg22-induced immunity, like stomatal closure, salicylic acid synthesis and callose deposition. These results suggest that chloroplasts play a central role in plant immunity. To examine the regulation of chloroplast function in immune response, we approached chloroplast proteomic analysis. At 2 h after treatment with flg22, amounts of some chloroplast-related proteins increased. In contrast, cas-1 did not show drastic changes in the amounts of the proteins in response to flg22 compared with wild-type plants. These results suggest that modifications of chloroplast proteins are important for plant immunity.
