title: Open Stomata 1 (OST1) is limiting in abscisic acid responses of Arabidopsis guard cells.
abstract: Open Stomata 1 (OST1) (SnRK2.6 or SRK2E), a serine/threonine protein kinase, is a positive regulator in abscisic acid (ABA)-mediated stomatal response, but OST1-regulation of K(+) and Ca(2+) currents has not been studied directly in guard cells and it is unknown whether OST1 activity is limiting in ABA-mediated stomatal responses. We employed loss-of-function and gain-of-function approaches to study native ABA responses of Arabidopsis guard cells. We performed stomatal aperture bioassays, patch clamp analyses and reactive oxygen species (ROS) measurements. ABA inhibition of inward K(+) channels and light-induced stomatal opening are reduced in ost1 mutants while transgenic plants overexpressing OST1 show ABA hypersensitivity in these responses. ost1 mutants are insensitive to ABA-induced stomatal closure, regulation of slow anion currents, Ca(2+) -permeable channel activation and ROS production while OST1 overexpressing lines are hypersensitive for these responses, resulting in accelerated stomatal closure in response to ABA. Overexpression of OST1 in planta in the absence of ABA application does not affect basal apertures or ion currents. Moreover, we demonstrate the physical interaction of OST1 with the inward K(+) channel KAT1, the anion channel SLAC1, and the NADPH oxidases AtrbohD and AtrbohF. Our findings support OST1 as a critical limiting component in ABA regulation of stomatal apertures, ion channels and NADPH oxidases in Arabidopsis guard cells.
authors.affiliation: Biology Department, Penn State University, University Park, PA, 16802, USA.
authors.forename: Biswa R
authors.initials: BR
authors.lastname: Acharya
authors.forename: Byeong Wook
authors.initials: BW
authors.lastname: Jeon
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Assmann
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D017360:Arabidopsis / Q000166:cytology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D015640:Ion Channel Gating / Q000187:drug effects; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D019255:NADPH Oxidases / Q000378:metabolism; D054046:Plant Stomata / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D030821:Plants, Genetically Modified; D015221:Potassium Channels / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D000040:Abscisic Acid; D029681:Arabidopsis Proteins; D015220:Calcium Channels; D019255:NADPH Oxidases; D015221:Potassium Channels; D011494:Protein Kinases; D017382:Reactive Oxygen Species; C472139:OST1 protein, Arabidopsis; C000589475:RBOH F protein, Arabidopsis
keywords: Ca2+-permeable channel; Open Stomata 1 (OST1); abscisic acid (ABA); guard cell; inward K+ channel; reactive oxygen species (ROS); slow anion channel; stomata