Abstract
Blue light perceived by phototropins (phot1 and phot2) mediates stomatal opening through the activation of the plasma membrane H+-ATPase via unknown signaling. A recent study has suggested the possible involvement of RPT2 (ROOT PHOTOTROPISM2), a BTB/POZ family protein functioning for phototropism, in the stomatal opening in response to blue light. However, conclusive evidence for the requirement of RPT2 in the activation process of the H+-ATPase and the stomatal opening has not been obtained so far. In this study, We have generated double mutants of RPT2 and phototropins, and investigated the blue light-specific stomatal responses in the mutants. We first confirmed the impaired hypocotyl phototropic response in rpt2 mutants. However, blue light-dependent H+ pumping from guard cell protoplasts and binding of a 14-3-3 protein to the H+-ATPase were not affected both in rpt2 single mutant and phot1rpt2 and phot2rpt2 double mutants. In accord with these results, the stomata of all rpt2 mutants opened in response to blue light in epidermal peels and intact leaves, suggesting that RPT2 is neither required for the activation of H+-ATPase nor stomatal opening.
