MdWRKY11 Participates in Anthocyanin Accumulation in Red-Fleshed Apples by Affecting MYB Transcription Factors and the Photoresponse Factor MdHY5

Red-fleshed apples are popular as a result of their high anthocyanin content. MdMYB10 and its homologues are known to be important regulators of anthocyanin synthesis in apple, but the roles of other transcription factors are not well-understood. Here, we explored the role of MdWRKY11 in regulating anthocyanin synthesis in apple flesh. Overexpression of MdWRKY11 in apple callus could significantly promote anthocyanin accumulation, and the expression of some MYB transcription factors and structural genes increased significantly. In binding analyses, MdWRKY11 bound to W-box cis-elements in the promoters of MdMYB10, MdMYB11, and MdUFGT. However, MdWRKY11 did not interact with MdMYB10, MdbHLH3, or MdWD40 proteins, the members of the MBW complex. Sequence analyses revealed that another W-box cis-element was present in the promoter of MdHY5 (encoding a photoresponse factor), and MdWRKY11 was able to bind to the promoter of MdHY5 and promote its activity. Our findings clarify the role of MdWRKY11 in anthocyanin synthesis in red-fleshed apple and imply that other novel genes may be involved in anthocyanin synthesis.