Threonine at position 306 of the KAT1 potassium channel is essential for channel activity and is a target site for ABA-activated SnRK2/OST1/SnRK2.6 protein kinase. Biochem J

Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama 6-6-07, Sendai 980-8579, Japan.
Biochemical Journal (Impact Factor: 4.4). 09/2009; 424(3):439-48. DOI: 10.1042/BJ20091221
Source: PubMed


The Arabidopsis thaliana K+ channel KAT1 has been suggested to have a key role in mediating the aperture of stomata pores on the surface of plant leaves. Although the activity of KAT1 is thought to be regulated by phosphorylation, the endogenous pathway and the primary target site for this modification remained unknown. In the present study, we have demonstrated that the C-terminal region of KAT1 acts as a phosphorylation target for the Arabidopsis calcium-independent ABA (abscisic acid)-activated protein kinase SnRK2.6 (Snf1-related protein kinase 2.6). This was confirmed by LC-MS/MS (liquid chromatography tandem MS) analysis, which showed that Thr306 and Thr308 of KAT1 were modified by phosphorylation. The role of these specific residues was examined by single point mutations and measurement of KAT1 channel activities in Xenopus oocyte and yeast systems. Modification of Thr308 had minimal effect on KAT1 activity. On the other hand, modification of Thr306 reduced the K+ transport uptake activity of KAT1 in both systems, indicating that Thr306 is responsible for the functional regulation of KAT1. These results suggest that negative regulation of KAT1 activity, required for stomatal closure, probably occurs by phosphorylation of KAT1 Thr306 by the stress-activated endogenous SnRK2.6 protein kinase.

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Available from: Taishi Umezawa
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    • "SnRK2.2 and SnRK2.3 regulate ABA responses in seed germination, dormancy, and seedling growth and are functionally redundant with SnRK2.6 (Fujii et al., 2007; Fujii and Zhu, 2009; Fujita et al., 2009; Nakashima et al., 2009). SnRK2.6 is expressed in guard cells and phosphorylates transcription factors, anion channels, and NADPH oxidase (RbohF), which synergistically regulates ABA-induced stomatal closure and plant drought tolerance (Mustilli et al., 2002; Kwak et al., 2003; Geiger et al., 2009; Lee et al., 2009; Sato et al., 2009; Sirichandra et al., 2009; Wege et al., 2014). ABA can be transported to guard cells in response to drought stress, inducing an efflux of ions, loss of turgor, and, thus, stomatal closure (Bray, 1997; Schroeder et al., 2001; Li et al., 2006; Mori et al., 2006). "
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    ABSTRACT: Abscisic acid (ABA) is a phytohormone that plays a fundamental role in plant development and stress response, especially in the regulation of stomatal closure in response to water deficit stress. The signal transduction that occurs in response to ABA and drought stress is mediated by protein phosphorylation and ubiquitination. This research identified Arabidopsis thaliana RING ZINC-FINGER PROTEIN34 (RZP34; renamed here as CHY ZINC-FINGER AND RING PROTEIN1 [CHYR1]) as an ubiquitin E3 ligase. CHYR1 expression was significantly induced by ABA and drought, and along with its corresponding protein, was expressed mainly in vascular tissues and stomata. Analysis of CHYR1 gain-of-function and loss-of-function plants revealed that CHYR1 promotes ABA-induced stomatal closure, reactive oxygen species production, and plant drought tolerance. Furthermore, CHYR1 interacted with SNF1-RELATED PROTEIN KINASE2 (SnRK2) kinases and could be phosphorylated by SnRK2.6 on the Thr-178 residue. Overexpression of CHYR1(T178A), a phosphorylation-deficient mutant, interfered with the proper function of CHYR1, whereas CHYR1(T178D) phenocopied the gain of function of CHYR1. Thus, this study identified a RING-type ubiquitin E3 ligase that functions positively in ABA and drought responses and detailed how its ubiquitin E3 ligase activity is regulated by SnRK2.6-mediated protein phosphorylation.
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    • "Subsequently, the phosphatase activity of PP2Cs is inhibited, which leads to autophosphorylation of SNF1-Related protein kinases (SnRK2s; Ma et al., 2009; Park et al., 2009; Santiago et al., 2009; Umezawa et al., 2009; Vlad et al., 2009). Stomatal closure is initiated by the depolarisation of guard cells, which is triggered by anion release through guard cell anion channel slow anion channel-associated 1 (SLAC1) (Geiger et al., 2009; Lee et al., 2009; Negi et al., 2008) and the inhibition of potassium channel 1 (KAT1) in Arabidopsis via phosphorylation mediated by OST1, a SnRK2 homologue (Joshi-Saha et al., 2011; Mustilli et al., 2002; Sato et al., 2009). Both channels facilitate the efflux of ions and are reciprocally regulated by the ABA signaling pathway and by Ca 2+ (Siegel et al., 2009). "
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    ABSTRACT: Being sessile organisms, plants are constantly exposed to various kinds of environmental stimuli. To survive under unfavorable environmental conditions they have evolved strategies to allow a balance between growth, reproduction and survival. In this review article, we first focus on two major abiotic stress factors, drought and heat, and briefly summarize the current knowledge on signal transduction pathways involved in plant responses to these stresses. In nature it is unlikely that plants are exposed to abiotic or biotic stresses in isolation. Hence, multiple stress situations are more likely to occur including heat, drought, salinity and pathogen attack. Since in many cases stress responses are antagonistic, predictions of molecular responses to multiple stresses based on single stress data is difficult or even impossible. Only recently, researchers started to study multiple-stress interactions and discovered for instance that plant responses to a combination of heat and drought differ from those to both single stresses. Moreover, abiotic stress applications are likely to influence plant-pathogen interactions and vice versa. Here, we discuss various aspects of multiple stress applications published within the last few years and pronounce the importance to study biotic and abiotic stress combinations in order to predict plant responses to future climate changes.
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    • "activates the anion channel SLOW ANION CHANNEL- ASSOCIATED 1 (SLAC1; Lee et al., 2009; Vahisalu et al., 2010), which has a central role in guard cells. Another ion channel targeted by SnRK2/OST1 is the KAT1 potassium channel, which loses its activity upon phosphorylation (Sato et al., 2009). The rise in cytoplasmic Ca 2+ concentration activates multiple calcium-dependent protein kinases CPK3, CPK6 (Mori et al., 2006), CPK4, CPK11 (Zhu et al., 2007), CPK5 (Dubiella et al., 2013), CPK21, and CPK23 (Geiger et al., 2010). "
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    ABSTRACT: In plants, fluctuation of the redox balance by altered levels of reactive oxygen species (ROS) can affect many aspects of cellular physiology. ROS homeostasis is governed by a diversified set of antioxidant systems. Perturbation of this homeostasis leads to transient or permanent changes in the redox status and is exploited by plants in different stress signalling mechanisms. Understanding how plants sense ROS and transduce these stimuli into downstream biological responses is still a major challenge. ROS can provoke reversible and irreversible modifications to proteins that act in diverse signalling pathways. These oxidative post-translational modifications (Ox-PTMs) lead to oxidative damage and/or trigger structural alterations in these target proteins. Characterization of the effect of individual Ox-PTMs on individual proteins is the key to a better understanding of how cells interpret the oxidative signals that arise from developmental cues and stress conditions. This review focuses on ROS-mediated Ox-PTMs on cysteine (Cys) residues. The Cys side chain, with its high nucleophilic capacity, appears to be the principle target of ROS. Ox-PTMs on Cys residues participate in various signalling cascades initiated by plant stress hormones. We review the mechanistic aspects and functional consequences of Cys Ox-PTMs on specific target proteins in view of stress signalling events. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email:
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