OST1 as a critical limiting component in ABA regulation of stomatal apertures

Photo credit: Wiley Online Library

A simplified schematic model for Open Stomata 1 (OST1) regulation of guard cell abscisic acid (ABA) signaling. This model integrates our data and information from the literature. Arrowheads represent activation, and short perpendicular bars indicate inhibition. PP2Cs, protein phosphatases 2Cs; ROS, reactive oxygen species; SLAC1, Slow Anion Channel 1; ICa, calcium current.

Open Stomata 1 (OST1) is limiting in abscisic acid responses of Arabidopsis guard cells.

by Acharya B. R., Jeon B. W., Zhang W., Assmann S. M. (2013)

in New Phytol. 200, 1049–1063. doi: 10.1111/nph.12469 –

PubMed Abstract | CrossRef Full Text | Google Scholar – MedlineWeb of Science


  • 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 Ca2+ 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, Ca2+-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.


Read the full article at: Wiley

Published by

Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.

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