Open stomata 1 kinase is essential for yeast elicitor-induced stomatal closure in arabidopsis

We recently demonstrated that yeast elicitor (YEL)-induced stomatal closure requires a Ca²⁺-dependent kinase, CPK6. A Ca²⁺-independent kinase, Open Stomata 1 (OST1), is involved in stomatal closure induced by various stimuli including ABA. In the present study, we investigated the role of OST1 in YEL-induced stomatal closure in Arabidopsis using a knock-out mutant, ost1-3, and a kinase-deficient mutant, ost1-2. YEL did not induce stomatal closure or activation of guard cell S-type anion channels in the ost1 mutants unlike in wild-type plants. However, YEL did not increase OST1 kinase activity in wild-type guard cells. The YEL-induced stomatal closure and activation of S-type anion channels were also impaired in a gain-of-function mutant of a clade A type 2C protein phosphatase (ABA INSENSITIVE 1), abi1-1C. In the ost1 mutants like in the wild type, YEL induced H₂O₂ accumulation, activation of non-selective Ca²⁺-permeable cation (I_Ca) channels and transient elevations in cytosolic free Ca²⁺ concentration ([Ca²⁺]_cyt) in guard cells. These results suggest that OST1 kinase is essential for stomatal closure and activation of S-type anion channels induced by YEL and that OST1 is not involved in H₂O₂ accumulation, I_Ca channel activation or [Ca²⁺]_cyt elevations in guard cells induced by YEL.