R2R3‐MYB transcription factor MdMYB23 is involved in the cold tolerance and proanthocyanidin accumulation in apple

Summary Cold stress severely affects plant growth and yield. C‐repeat binding factors ( CBF s) play important roles in the response to cold stress. In the present study, we identified an R2R3‐ MYB transcription factor ( TF ) Md MYB 23 from apple ( Malus × domestic ) using transcriptome analyses, which was notably induced in response to cold stress. Transgenic apple calli and Arabidopsis with overexpression of Md MYB 23 exhibited increased cold tolerance. Electrophoretic mobility shift assay ( EMSA ) and transient expression assays indicated that Md MYB 23 directly bound to the promoters of Md CBF 1 and Md CBF 2 and activated their expression. Md MYB 23 interacted with the promoter of Md ANR , a key modulator of proanthocyanidin biosynthesis, and activated its expression to promote proanthocyanidin accumulation and reactive oxygen species ( ROS ) scavenging. Md BT 2 was identified as an Md MYB 23‐interacting protein using yeast two‐hybrid (Y2H), pull‐down, and bimolecular fluorescence complementation (Bi FC ) assays. Md BT 2 repressed cold tolerance and proanthocyanidin accumulation by promoting the degradation of Md MYB 23 protein. Our findings shed light on the functions of MYB TF s and underlying mechanism in the modulation of plant cold tolerance.