Figure 4.

Model for phosphorylation-dependent re-localization of PINs. De novo synthesized PINs are distributed apolarly to the PM. Constitutive endocytosis relocates PINs depending on their phosphorylation status (red dots). This relocation might be baso-apical as in the figure (embryo, root, shoot, and inflorescence meristem), apolar-lateral (phototropism), between lobe and indentation (pavement cells), or between the inner or outer cell side (guard cells). Tuning of the activities of AGC kinases and PP6-type phosphatase determines the PIN phosphorylation status and thus the preferential targeting pathway, and leads to the respective redistribution of the PINs. Basal targeting of unphosphorylated PINs is GNOM-dependent; ARF-GEFs involved in other targeting pathways remain unknown. Grey arrows indicate trafficking of PIN-loaded vesicles, while black arrows indicate the direction of PIN-mediated auxin transport.