Figure 10.

Proposed model for the ethylene-inhibited anthocyanin biosynthesis via the PpERF9-PpTPL1 co-repressor complex-mediated histone deacetylation in pear fruit. In the presence of ethylene, the expression of PpERF9 is induced. Additionally, PpERF9 interacts with the PpTPL1 co-repressor to form a complex that removes the acetyl group on histone H3 and maintains a low H3ac level in the promoter regions of PpERF9-targeted genes (PpRAP2.4 and PpMYB114) to repress their expression. On the one hand, PpERF9 binds to the PpMYB114 promoter and inhibits its expression via PpERF9-PpTPL1-mediated histone deacetylation, directly inhibiting anthocyanin biosynthesis in pear fruit. On the other hand, PpERF9 inhibits the expression of PpRAP2.4 via histone deacetylation. PpRAP2.4 induces the expression of PpMYB114 by binding to its promoter. Thus, a PpERF9-PpRAP2.4-PpMYB114 regulatory pathway inhibits anthocyanin biosynthesis in pear fruit. Furthermore, ethylene signaling also induces the expression of PpERF105, which then activates PpMYB140, a transcriptional repressor of anthocyanin biosynthesis by competing with PpMYB114 to form the MBW complex, which finally inhibits anthocyanin biosynthesis in pear fruit.