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.