Abstract
Plants defend themselves against pathogens by a sophisticated innate immune system. The primary immune response is induced by Microbe-associated molecular patterns (MAMPs). MAMPs receptors recognize the presence of pathogens and turn on an appropriate basal defense response. Since stomata are one of the main entry pathways of pathogenic invaders, plants have developed an active system to close stomata quickly in response to pathogen attack. However, its molecular mechanism is largely unknown. Previously, we demonstrated that elicitors could induce a transient increase in stromal Ca2+ concentration within a few minutes. This implies that chloroplasts could quickly recognize the extracellular pathogens via Ca2+ signaling. CAS is a plant-specific Ca2+-binding protein that is localized in chloroplast thylakoid membranes. In this study, we found that CAS is essential for flg22-induced stomatal closure in Arabidopsis. Furthermore, we revealed that CAS is also involved in the flg22-induced expression of pathogen-related genes (PR-1). These results imply that chloroplast protein CAS is crucial for plant innate immune response, such as MAMP-induced stomatal closure.
