Abstract
Phototropins, autophosphorylating protein kinases, mediate stomatal opening through activation of the plasma membrane H+-ATPase via phosphorylation in response to blue light. However, the mechanism by which the signal from phototropins is transduced into H+-ATPase activation remains unknown. Here we show that protein phosphatase 1 (PP1) mediates stomatal opening by blue light. Transient expression of guard cells with mutant type of catalytic subunit of PP1 that lost the catalytic activity, or inhibitor-2, a specific inhibitor protein of PP1 suppressed blue light-dependent stomatal opening. Furthermore, tautomycin, a cell-permeable inhibitor of PP1, impaired the phosphorylation of the H+-ATPase in response to blue light without affecting that of phototropins. These separate lines of evidence indicate the function of PP1 as a positive regulator between phototropins and the H+-ATPase in the blue light signaling of guard cells.
