MdHY5 positively regulates cold tolerance via CBF-dependent and CBF-independent pathways in apple.

Cold stress is a major external stimulator that affects crop quality and productivity. The CBF cold regulatory pathway has been regarded as a master regulator in the response to cold stress. In this study, we found that the apple bZIP transcription factor, MdHY5, was responsive to cold treatment both at the transcriptional and at the post-translational levels. Moreover, overexpression of MdHY5 enhanced cold tolerance in apple calli and Arabidopsis. Subsequently, EMSA assay and transient expression assay demonstrated that MdHY5 positively regulated the transcript of MdCBF1 by binding to G-Box motif of its promoter. Furthermore, MdHY5 also regulated the expression of CBF-independent cold-regulated genes. Taken together, our data suggest that MdHY5 positively modulates plant cold tolerance through CBF-dependent and CBF-independent pathways, providing a deeper understanding of MdHY5-regulated cold tolerance in apple.