The phosphorylation code is implicated in cell type-specific trafficking of PIN-FORMEDs

The subcellular polarity of PIN-FORMEDs (PINs) is critical for directional cell-to-cell transport of auxin. Phosphorylation of PIN proteins plays an important role in generating and maintaining specific PIN polarity. In a recent study, we have shown that phosphorylation in certain conserved residues of the PIN3 hydrophilic loop (HL) modulates its subcellular localization and polarity in a cell type-specific manner in different root tissues. Here, we additionally show that the phosphorylation code of PIN3-HL is operational for the determination of PIN3 polarity in the Arabidopsis guard cell and is deciphered in a differential way even in a single tobacco cell for the intracellular trafficking of PIN3. On the other hand, PIN3 localization often remained unaltered in certain cell types irrespective of its phosphorylation status. These findings, together with previous reports, indicate that the phosphorylation code of the PIN-HL along with cell type-specific factors, kinases, and developmental/environmental cues is instrumental for the PIN trafficking to different subcellular compartments as well as different plasma membrane domains.