Figure 8.

A model for drought adaptation mediated by MdMYB88 and MdMYB124 in apple roots. In apple roots, drought stress activates MdMYB88 and MdMYB124, which then directly target the promoters of MdVND6 and MdMYB46 and induce their expression. Up-regulated MdMYB46 expression enhances drought tolerance by regulating root xylem vessel formation, which results in a greater hydraulic conductivity and thus drought adaptation. Increased expression of MdMYB46 also activates downstream genes associated with cellulose and lignin biosynthesis, resulting in cellulose and lignin deposition as well as drought adaptation.