Phosphorylation of BLUS1 kinase by phototropinsis a primary step in stomatal opening

摘要

Opening of stomata in the plant facilitates photosynthetic CO2 fixation and transpiration.Blue-light perception by phototropins (phot1, phot2) activates the plasma membraneH~+-ATPase, causing stomata to open. Here we describe a regulator that connects thesecomponents, a Ser/Thr protein kinase, BLUS1 (BLUE LIGHT SIGNALING1), which mediates aprimary step for phototropin signalling in guard cells. blus1 mutants identified by infraredthermography result in a loss of blue light-dependent stomatal opening. BLUS1 encodes aprotein kinase that is directly phosphorylated by phot1 in vitro and in vivo at Ser-348 within itsC-terminus. Both phosphorylation of Ser-348 and BLUS1 kinase activity are essential foractivation of the H~+-ATPase. blus1 mutants show lower stomatal conductance and CO2assimilation than wild-type plants under decreased ambient CO2. Together, our analysesdemonstrate that BLUS1 functions as a phototropin substrate and primary regulator ofstomatal control to enhance photosynthetic CO2 assimilation under natural light conditions.