Open stomata 1 (OST1) kinase controls R–type anion channel QUAC1 in Arabidopsis guard cells

Abstract

SUMMARYUnder drought stress, the stress hormone ABA addresses the SnR kinase OST1 via its cytosolic receptor and the protein phosphatase ABI1. Upon activation, OST1 phosphorylates the guard cell S-type anion channel SLAC1. Arabidopsis ABI1 and OST1 loss-of-function mutants are characterized by an extreme wilting 'open stomata′ phenotype. Given the fact that guard cells express both SLAC-and R-/QUAC-type anion channels, we questioned whether OST1, besides SLAC1, also controls the QUAC1 channel. In other words, are ABI1/OST1 defects preventing both of the guard cell anion channel types from operating properly in terms of stomatal closure? The activation of the R-/QUAC-type anion channel by ABA signaling kinase OST1 and phosphatase ABI1 was analyzed in two experimental systems: Arabidopsis guard cells and the plant cell-free background of Xenopus oocytes. Patch-clamp studies on guard cells show that ABA activates R-/QUAC-type currents of wild-type plants, but to a much lesser extent in those of abi1-1 and ost1-2 mutants. In the oocyte system the co-expression of QUAC1 and OST1 resulted in a pronounced activation of the R-type anion channel. These studies indicate that OST1 is addressing both S-/SLAC-and R-/QUACtype guard cell anion channels, and explain why the ost1-2 mutant is much more sensitive to drought than single slac1 or quac1 mutants.

Reactive Oxygen Species in the Regulation of Stomatal Movements

“…As inferred from genetic evidence, patch-clamp studies in guard cells, in vitro kinase assays, and channel activity assays upon coexpression of the components in Xenopus laevis oocytes, OST1 is then thought to bind and activate by phosphorylation the guard cell anion channels SLOW ANION CHANNEL-ASSOCIATED1 (SLAC1) and QUICK-ACTIVATING ANION CHANNEL1 (QUAC1) leading to stomatal closure ( Figs. 1 and 2; Lee et al, 2009;Imes et al, 2013). It should be noted that phosphorylation of the N terminus of SLAC1 by OST1 has been detected only in vitro.…”

SUCROSE NONFERMENTING1-RELATED PROTEIN KINASE2.6, an Ortholog of OPEN STOMATA1, Is a Negative Regulator of Strawberry Fruit Development and Ripening

“…B, Phylogenic analysis of SnRK2 2011; Hrabak et al, 2013). OPEN STOMATA1 (OST1), also designated as SnRK2E or SnRK2.6, is a member of the SnRK2 family that plays a critical role in stomatal movement, and in Arabidopsis (Arabidopsis thaliana), mutation of OST1 renders guard cells insensitive to ABA, such that stomata remain open in the presence of ABA (Schroeder et al, 2001;Mustilli et al, 2002;Assmann, 2003;Yoshida et al, 2006;Imes et al, 2013). OST1 and its orthologs in other plant species are thought to have important roles in various biological processes in addition to their involvement in stomatal regulation (Sirichandra et al, 2010;Zheng et al, 2010;Xue et al, 2011;Imes et al, 2013;Vilela et al, 2013;Wang et al, 2013a).…”

A molecular pathway for CO2 response in Arabidopsis guard cells

“…OST1 can also interact and activate R-type channel QUAC1 (ref. 33). Therefore, OST1 is a central transducer of ABA and CO 2 signal pathways in guard cells 6,18 .…”