Roles of pepper bZIP protein CaDILZ1 and its interacting partner RING-type E3 ligase CaDSR1 in modulation of drought tolerance

Abscisic acid (ABA) is a plant hormone that plays a key role in the environmental stress response, especially the induction of ABA-responsive and stress-responsive genes and modulation of the stomatal aperture in response to drought stress. Here, we identified CaDILZ1 (Capsicum annuum Drought-Induced Leucine Zipper 1) belonging to subgroup D of the bZIP protein family; gene functions of this family in response to ABA and drought signaling still remain unknown. CaDILZ1 expression was significantly induced in pepper leaves after exposure to ABA, drought, and NaCl. The CaDILZ1 protein localized in the nucleus of plant cells. In response to drought stress, CaDILZ1-silenced pepper and CaDILZ1-overexpressing Arabidopsis plants exhibited drought-sensitive and drought-tolerant phenotypes, respectively, via altered ABA content, stomatal closure, and expression of ABA-responsive and drought-responsive marker genes. We isolated the RING finger protein CaDSR1 (CnnuumDrought Sensitive RING finger protein 1), which interacted with CaDILZ1 in the nucleus. The CaDSR1 protein exhibited E3 ligase activity and promoted CaDILZ1 degradation via the 26S proteasome pathway. Under drought stress conditions, CaDSR1-silenced pepper and CaDSR1-overexpressing Arabidopsis plants exhibited contrasting phenotypes to those of CaDILZ1-silenced pepper and CaDILZ1-overexpressing Arabidopsis plants. Taken together, our data suggest that CaDSR1 and CaDILZ1 function in ABA-mediated drought stress signaling in pepper plants. Significance Statement The signal transduction occurring in response to drought stress is mediated from transcription to post-translational modification. Here, the stress-inducible pepper bZIP protein CaDILZ1 from subgroup D positively regulated ABA-mediated drought responses, whereas RING-type E3 ligase CaDSR1 played a contrasting role and triggered ubiquitination and degradation of CaDILZ1; our findings reveal a regulatory mechanism that links CaDILZ1 and CaDSR1 in the drought tolerance and ABA-mediated responses in pepper plants.