Pepper E3 ligase CaAIRE1 promotes ABA sensitivity and drought tolerance by degradation of protein phosphatase CaAITP1.

Plants have developed defense mechanisms to survive in extreme environmental conditions. Abscisic acid (ABA) is a key phytohormone associated with plant adaptation to environmental stress. In this study, we isolated and functionally characterized the pepper RING-type E3 ligase CaAIRE1 (Capsicum annuum ABA Induced RING-type E3 ligase 1) containing the C3HC4-type RING domain. CaAIRE1 was induced by ABA and drought, and CaAIRE1 had E3 ligase activity. CaAIRE1-silenced pepper and CaAIRE1-overexpressing Arabidopsis presented drought-sensitive and drought-tolerant phenotypes, respectively, which were accompanied by altered transpiration water loss and ABA sensitivity. Moreover, we found that CaAIRE1 interacts with and ubiquitinates the pepper type 2C protein phosphatase, CaAITP1 (Capsicum annuum CaAIRE1 Interacting Target Phosphatase 1). A cell-free degradation assay with CaAIRE1-silenced peppers and CaAIRE1-overexpressing Arabidopsis plants revealed that the CaAITP1 protein level was negatively modulated by the expression level of CaAIRE1. In contrast to CaAIRE1, CaAITP1-silenced pepper showed ABA-sensitivity phenotypes. CaAITP1-overexpressing Arabidopsis plants were the most insensitive phenotypes to ABA compared with the wild type and other pepper PP2C-overexpressing plants. Taken together, our data indicate that CaAITP1 plays a major role as a negative modulator in ABA signaling, and CaAIRE1 regulates the ABA signaling and drought response through modulation of CaAITP1 stability.