Fig. 8.

A model summarizing the upregulation of STM expression prior to AM initiation through the licensing of active DRN/DRNL-REV complexes by ZPRs. In the early leaf axil, ZPR3 is expressed and interacts with REV to inhibit the formation of functional DRN/DRNL-REV complexes, resulting in a low level of STM expression and the absence of axillary bud formation. As the leaf matures, decreasing ZPR3 levels allow the formation of DRN/DRNL-REV complexes in more mature leaf axils to upregulate STM expression and to promote axillary bud formation.