ABSTRACT Homeodomain‐leucine zipper (HD‐ZIP) transcription factors, particularly subfamily I genes, are associated with drought stress responses. However, the functional roles of HD‐ZIP subfamily II genes, particularly in pepper ( Capsicum annuum ), remain inadequately studied, and their involvement in abscisic acid (ABA) signalling is not fully elucidated. In this study, we isolated the HD‐ZIP subgroup II gene CaDRHB12 ( C. annuum drought‐responsive homeobox gene 12), which shares sequence homology with CaHAT1, a previously identified positive regulator of drought tolerance. Unlike that of CaHAT1 , CaDRHB12 expression was significantly downregulated upon ABA and drought stress treatment. Functional analyses of CaDRHB12 in pepper and Arabidopsis plants revealed that CaDRHB12 negatively regulates ABA signalling and drought stress responses. Furthermore, CaDRHB12 interacted with CaSnRK2.6, an ABA signalling‐related kinase that associates with and phosphorylates CaHAT1. In vitro and in vivo kinase assays demonstrated that CaSnRK2.6 also directly phosphorylates CaDRHB12, promoting CaDRHB12 protein degradation. This degradation was not observed in CaDRHB12 phospho‐dead and CaSnRK2.6 kinase‐dead mutants. Additionally, the transcriptional activity of CaDRHB12 was influenced by its phosphorylation status and CaSnRK2.6 function, highlighting the critical role of CaSnRK2.6‐mediated phosphorylation in regulating CaDRHB12 protein. Collectively, our findings suggest that CaDRHB12 negatively regulates pepper drought tolerance, and its protein stability is modulated by CaSnRK2.6‐mediated phosphorylation under drought stress conditions. Understanding the role of CaDRHB12 in drought stress response aids in developing strategies to improve plant resilience to abiotic stresses, potentially leading to more robust crops.
Baek et al. (Wed,) studied this question.