Abstract
Chloroplasts are involved in the synthesis of stress hormones such as jasmonic acid and production of ROS. However, very little is known about the role of chloroplasts in plant defense responses. We recently found that various biotic (flg22 and chitin) or abiotic stresses (NaCl, sorbitol and H2O2) induced the elevation of stromal Ca2+ concentration in Arabidopsis. The chloroplast localized putative Ca2+ binding protein CAS is involved in the generation of these stromal Ca2+ signals. In this study, we found that high salinity-induced chlorosis was accelerated in theCAS knockout mutants. On the other hand, effecter-induced hypersensitive cell death and elicitor flg22- and high osmolarity-induced anthocyanin synthesis were delayed significantly in CAS knockout mutants. Furthermore, we revealed that CAS is involved in the flg22-induced PR1 gene expression (SA pathway). These results suggest that CAS might play a critical role in the promotion of defense responses against these stresses.
