Abstract
Protein phosphatase 1 (PP1) consists of a catalytic subunit (PP1c) and multiple regulatory subunits that determine the catalytic activity, the subcellular localization, and the substrate specificity. Previously, we have demonstrated that PP1 mediates blue light signaling between phototropins and the plasma membrane H+-ATPase in guard cells. However, the molecular mechanisms by which PP1 transmits the blue light signal and the regulatory subunit acts for this response remain unclear. Here we identified a plant specific PP1 regulatory subunit PRS2, which is expressed in guard cells. Arabidopsis genome contains nine PRS2-like proteins, and two of them are bound to PP1c through RVxF motif in PRSs, a PP1c binding sequence. Arabidopsis prs2 double mutants showed reduced blue light-dependent stomatal opening, H+ pumping, and phosphorylation of the H+-ATPase, but showed normal phosphorylation of phototropins. Wild type PRS2 complemented prs2 phenotype, but RVxF motif mutation did not. Tautomycin, an inhibitor of PP1c, mimicked the prs2 phenotype. These results suggest that PRS2 function as a regulatory subunit of PP1 and regulates blue light signaling between phototropins and H+-ATPase.
