A feedback loop involving MdMYB108L and MdHY5 controls apple cold tolerance.

The MYB transcription factors are important for many aspects of plant stress responses. In this study, we isolated and identified an apple MYB gene, MdMYB108L, whose expression is induced by light and cold stresses. An analysis of MdMYB108L-overexpressing transgenic apple calli revealed that MdMYB108L enhances cold tolerance in apple by upregulating MdCBF3 expression. Interestingly, the expression of MdHY5, which encodes an integrator of light and cold signals, was significantly downregulated in transgenic calli. Yeast one-hybrid and electrophoretic mobility shift assays indicated that MdMYB108L positively regulates cold tolerance by binding to the MdCBF3 promoter. Additionally, MdHY5 functions upstream of MdMYB108L, and the resulting increase in MdMYB108L abundance downregulates MdHY5 transcription. The results of this study elucidate a new pathway for the regulation of apple cold tolerance via a feedback mechanism involving MdMYB108L and MdHY5.