Phosphorylation of plant plasma membrane aquaporins regulates ion channel function

McGaughey SA1, Qiu J1, Groszmann M2, Tyerman SD1 and Byrt CS1

  1. ARC Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, The University of Adelaide, SA, Australia, 5006.
  2. ARC Centre of Excellence for Translational Photosynthesis, Australian National University.

Phosphorylation on the C-terminal domain (CTD) of Arabidopsis plasma membrane aquaporin AtPIP2;1 may be key to its ion channel function. AtPIP2;1 has previously been identified as a Na+ permeable functional water channel. A series of phospho-mimic mutant AtPIP2;1 proteins were expressed in X. laevis oocytes. Phospho-mimic mutations of two CTD residues of AtPIP2;1 had significantly increased Na+ conductivity compared to WT AtPIP2;1. Interestingly, the apparent water permeability of the phospho-mimic AtPIP2;1 mutants were lower than that of WT AtPIP2;1 when PIP expressing X. laevis oocytes were transferred from isotonic to hypotonic solutions that had equivalent ion concentrations. These results suggest that (i) phosphorylation has an important role in the regulation of ion channel function of ion permeable plant aquaporins and (ii) that there may be an inverse relationship between ion permeability and water permeability of these aquaporins. As plant plasma membrane aquaporins are very important for water uptake and transcellular water flow in plant roots, PIPs with ion channel functions may constitute a mechanism by which Na+ enters plant roots in saline conditions. However the exact physiological role of dual water ion plant aquaporins is yet to be elucidated.