As research progresses on how guard cells perceive and transduce environmental cues to regulate stomatal movement, plant biologists are discovering key roles of protein phosphorylation. Early research efforts focused on characterization of ion channels and transporters in guard cell hormonal signaling. Subsequent genetic studies identified mutants of kinases and phosphatases that are defective in regulating guard cell ion channel activities, and recently proteins regulated by phosphorylation have been identified. Here we review the essential role of protein phosphorylation in ABA-induced stomatal closure and in blue light-induced stomatal opening. We also highlight evidence for the cross-talk between different pathways, which is mediated by protein phosphorylation.
Keywords: AAPK, ABA activated protein kinase; ABA; ABA, abscisic acid; ABI, abscisic acid insensitive; AHK5, Arabidopsis histidine kinases 5; AKS, ABA-responsive kinase substrates; BL, blue light; BLUS1, blue light signaling1; CBL, calcineurin-B like proteins; CIPK, CBL-interacting protein kinase; CPK, calcium dependent protein kinase; EPs, epidermal peels; GCPs, guard cell protoplasts; GHR1, guard cell hydrogen peroxide-resistant1; HAB1, homology to ABI1; HRB1, hypersensitive to red and blue 1; HXK, hexokinase; IHC, immunohistochemistry; KAT1, K+ channel in A. thaliana 1; LC-MS/MS, liquid chromatography–mass spectrometry; MAP4K, mitogen-activated protein kinase kinase kinase kinase; MPK, mitogen-activated protein kinase; MeJA, methyl jasmonate; NO, nitric oxide; OST1, open stomata 1; PA, phosphatidic acid; PHO1, phosphate1; PP1, protein phosphatase; PP7, protein phosphatase; PRSL1, PP1 regulatory subunit2-like protein1; PTPases, protein tyrosine phosphatases; QUAC1, quickly-activating anion channel 1; RBOH, respiratory burst oxidase homolog; ROS; ROS, reactive oxygen species; SLAC1, slow anion channel-associated 1; SnRK2.6, sucrose nonfermenting-1 (Snf1)-related protein kinase 2.6; blue light; guard cell, ion channel; kinase; phosphatase; protein phosphorylation.