Roles of pepper bZIP transcription factor CaATBZ1 and its interacting partner RING-type E3 ligase CaASRF1 in modulation of ABA signalling and drought tolerance.

Ubiquitination is a eukaryotic protein modulation system for identifying and affecting proteins that are no longer needed in the cell. In a previous study, we elucidated the biological function of CaASRF1, which contains a RING finger domain and functions as an E3 ligase. We showed that CaASRF1 positively modulates abscisic acid (ABA) signalling and drought stress tolerance by modulating the stability of subgroup D bZIP transcription factor CaAIBZ1. We performed yeast two-hybrid (Y2H) screening to identify an additional target protein of CaASRF1. In this study, we identified pepper CaATBZ1 (Capsicum annuum ASRF1 target bZIP transcription factor 1), which belongs to the subgroup A bZIP transcription factors. We investigated the biological function of this protein using virus-induced gene silencing (VIGS) in pepper plants and by generating overexpressing transgenic Arabidopsis plants. Our loss-of-function and gain-of-function studies revealed that CaATBZ1 negatively modulates ABA signalling and drought stress response. Consistent with CaATBZ1-silenced pepper plants, CaASRF1/CaATBZ1-silenced pepper plants displayed drought-tolerant phenotypes via ABA-mediated signalling. Our results demonstrated that CaASRF1-mediated ubiquitination plays a crucial role in regulating the stability of CaATBZ1. These findings provide valuable insight into the post-translational regulation of transcriptional factors.