Latest finding - Molecular and Developmental Genetics
- Phosphorylation of conserved PIN motifs by PINOID controls Arabidopsis PIN1 polar targeting
Polar cell-to-cell transport of the plant hormone auxin by PIN FORMED (PIN) auxin efflux carriers generates auxin maxima and minima that provide positional information for many developmental processes, such as tropic growth and organ formation. PIN proteins determine the direction of auxin flow by their asymmetric subcellular distribution at the plasma membrane. The apical-basal polar localization of the PIN proteins is controlled by antagonistic action of the PINOID (PID) AGC kinase and PP2A phosphatases on the phosphorylation status of the PIN central hydrophilic loop (PINHL).
Recently, we were able to show that PID phosphorylates PIN1 at serine residues in three conserved motifs within the PIN1HL. Loss-of-phosphorylation PIN1 proteins in which the serines were substituted by alanines induced embryo and inflorescence defects, correlating with a basal localization of these mutant carriers. Conversely, the phosphomimic PIN1 proteins in which the serines were replaced with glutamic acids showed apical localization in the shoot apex, but still induced pin-formed inflorescences, revealing the importance of the reversibility of phosphorylation.
Collectively, our data indicate that reversible phosphorylation of the conserved motifs in the PIN1HL by PID is required and sufficient for proper PIN1 polar targeting to the plasma membrane, and that this is essential for generating the differential auxin distribution that directs embryo and inflorescence development.
Fang Huang, Marcelo Kemel-Zago, Arnoud van Marion, Carlos Galvan-Ampudia and Remko Offringa describe these findings in a manuscript that has been submitted for publication in The Plant Cell.
