Figure 7. Schematic representation of PIN1 protein regulation by strigolactone and its effect on bud activity.

Strigolactone, signalling via MAX2, depletes PIN1 from the PM of cells in the shoot, for example by promoting clathrin-mediated endocytosis. Strigolactone acts systemically, influencing PM PIN1 levels throughout the shoot. In the main stem, PIN1 on the PM is at steady state. In an activating bud, canalization is underway, with rapid PIN1 insertion, outstripping PIN1 removal. In an inhibited bud, PIN1 insertion is slower than PIN1 depletion, such that PIN1 does not accumulate on the PM [20],[23]. Systemically higher strigolactone levels will reduce the number of active buds and the steady-state levels of PM PIN1. Systemically lower strigolactone will have the opposite effect.