(The) M3 phosphorylation region of PIN-FORMEDs plays for their polarity and biological roles in arabidopsis

Abstract

Asymmetrically localized PIN-FORMED (PIN) auxin efflux carriers play an important role in regulating directional intercellular auxin movement and thus generating local auxin gradients. The polar localization of PINs is tightly controlled by phosphorylation in the central hydrophilic loop (HL) of PINs. The importance of M3 phosphorylation site, which locates in evolutionarily conserved RKSNASRRSF(/L) and TPRPSNL motifs of the HL, has been reported for PIN3. Here, we analyzed the conserved role of the M3 phosphorylation site of PIN1 and PIN7. Phosphorylation-defective mutations of five phosphorylatable residues (Ser/Thr to Ala or Gly) in the M3 site of PIN1-HL changed its subcellular polarity and caused defects in PIN1-mediated biological functions such as floral organ formation, root growth and leaf phyllotaxy. The M3 phosphorylation-defective mutants of PIN7 impaired its proper subcellular trafficking in root columella cells, which then disrupted normal root gravitropism. Our data indicate that the M3 phosphorylation site is functionally conserved among long PINs and plays important roles for their subcellular trafficking, auxin distribution, and auxin-mediated developmental processes.