The M3 Phosphorylation Site Is Required for Trafficking and Biological Roles of PIN-FORMED1, 2, and 7 in .

Asymmetrically localized PIN-FORMED (PIN) auxin efflux carriers play key roles in regulating directional intercellular auxin movement, generating local auxin gradients, and diverse auxin-mediated growth and development. The polar localization of PINs is controlled by phosphorylation in the central hydrophilic loop (HL) of PINs. Although the M3 phosphorylation site, including phosphorylatable 5 Ser/Thr residues, is conserved among long HL-PINs, its native role has only been characterized in PIN3.