The open stomata 1-like protein-coding sequence encodes a sucrose non-fermenting 1-related protein kinase 2-type serine/threonine protein kinase. OST1/SnRK2.6 is a major ABA-related kinase controlling stomatal closure in Arabidopsis thaliana. In plants, OST1-type kinases are activated by increased abscisic acid levels. In barley, OST1-like kinases, particularly HvSnRK2.7 and HvSnRK2.9, are involved in stomatal regulation and contribute to guard-cell responses to abscisic acid, vapor pressure deficit and water-loss control. In guard cells, OST1/SnRK2-type kinases phosphorylate downstream ion-channel and signaling proteins, promoting anion efflux, membrane depolarization, loss of guard-cell turgor and stomatal closure. The protein is therefore relevant to molecular pathways controlling water loss, drought response and stomatal aperture.