The HD-Zip I transcription factor MdHB-7 regulates drought tolerance in transgenic apple (Malus domestica)

•This study revealed the HD-Zip I transcription factor MdHB-7 contributes to the water deficit response in transgenic apple.•Through drought stress treatments and phenotypic assessments, we found that MdHB-7 expression enhanced the drought tolerance of apple plants.•Our results lay a foundation for further research on the mechanisms by which HD-Zip I proteins promote drought tolerance. Drought severely restricts global crop yield and quality. These limitations may be partially addressed through genetic engineering to improve crop drought tolerance. The HD-Zip I transcription factors play important roles in the regulation of plant drought tolerance, but their specific functions in the regulation of apple drought response remain unclear. In this study, we found that MdHB-7 was expressed at different levels in a variety of apple tissues and was significantly induced by abscisic acid (ABA) and drought stress treatments. To investigate the functions of MdHB-7, we created transgenic apple plants that exhibited either MdHB-7 overexpression or RNAi-induced MdHB-7 suppression. Through drought stress treatments and phenotypic assessments, we found that MdHB-7 expression enhanced the drought tolerance of apple plants. Overexpression of MdHB-7 promoted endogenous ABA accumulation, stomatal closure, and reactive oxygen species (ROS) detoxification in response to drought, whereas suppression of MdHB-7 expression had the opposite effect. Our results lay a foundation for further research on the mechanisms by which HD-Zip I proteins promote drought tolerance.