MdWRKY75 regulates MdCAR4 ‐mediated ABA receptor turnover to enhance drought resistance in apple

Drought is one of the most severe abiotic stresses leading to reduced crop yield. Stomatal closure mediated by abscisic acid (ABA) signaling is a critical drought resistance mechanism in plants. Previously, we identified a drought-responsive apple transcription factor, MdWRKY75, from the drought transcriptome, which positively regulates apple drought resistance. Overexpression of MdWRKY75 results in smaller stomatal apertures than wild-type (WT) plants, elevated ABA content, and increased expression of ABA signaling pathway genes, whereas RNA interference (RNAi) lines exhibit the opposite effect. Furthermore, MdWRKY75 binds to the promoter of ABA signaling pathway gene C2-domain ABA-related 4 (MdCAR4) and positively regulates its expression. MdCAR4-RNAi plants are less drought-tolerant than WT plants, with lower stomatal aperture and ABA content, while MdCAR4 overexpression enhances drought resistance and rescues the drought-sensitive phenotype of MdWRKY75-Ri3. In addition, MdCAR4 interacts with ABA receptor family member MdPYL3/4.2/5/6, enhancing their localization to the plasma membrane. Finally, MdPYL3/4.2/5/6 also positively regulates ABA-mediated stomatal closure and drought tolerance, and their overexpression rescues the drought-sensitive phenotype of MdCAR4-Ri5. Our findings demonstrate that the MdCAR4-MdPYLs interaction module, regulated by MdWRKY75, promotes ABA signaling and enhances apple drought resistance by increasing the plasma membrane localization of ABA receptors.