Figure 11.

Model showing the regulatory mechanism of MdNAC7‐MdWRKY31 module in regulating apple fruit softening by modulating the expression of MdXTH2. Under air conditions, a sufficient amount of the MdWRKY31 protein directly binds to the promoter of MdXTH2 and represses MdXTH2 expression, thus delaying fruit softening and maintaining fruit firmness. However, when ethylene is present, ethylene signalling significantly reduces and increases the abundance of MdWRKY31 and MdNAC7, respectively. In this case, almost all MdWRKY31 proteins are interacted by MdNAC7 proteins to form MdWRKY31‐MdNAC7 protein complexes, thereby hindering MdWRKY31 from binding to MdXTH2 promoter. These occurrences ultimately result in ethylene‐mediated apple fruit softening.