Abstract
Phototropins (phot1 and phot2), autophosphorylating protein kinases, mediate stomatal opening through activation of the plasma membrane H+-ATPase via phosphorylation in response to blue light (BL). However, the mechanism by which the signal from phototropins is transduced into H+-ATPase activation is unknown. We investigated the effect of tautomycin (TAU), a specific inhibitor of type1 and type2A protein phosphatases, on BL-dependent responses to elucidate the role and location of protein phosphatase in BL signaling. Stomatal opening in epidermal strips and H+ pumping in Vicia guard cell protoplasts in response to BL were strongly inhibited by TAU. Furthermore, TAU inhibited both BL-induced phosphorylation of the H+-ATPase and subsequent binding of 14-3-3 proteins. However, BL-induced autophosphorylation of phototropins was not affected by TAU. These results suggest that a TAU-sensitive protein phosphatase functions as a positive regulator in guard cell BL signaling downstream phototropins and upstream the H+-ATPase.
