SLAC1 is required for plant guard cell S-type anion channel function in stomatal signalling

Abstract

Stomatal pores, formed by two surrounding guard cells in the epidermis of plant leaves, allow influx of atmospheric carbon dioxide in exchange for transpirational water loss. Stomata also restrict the entry of ozone-an important air pollutant that has an increasingly negative impact on crop yields, and thus global carbon fixation 1 and climate change 2 . The aperture of stomatal pores is regulated by the transport of osmotically active ions and metabolites across guard cell membranes 3,4 . Despite the vital role of guard cells in controlling plant water loss 3,4 , ozone sensitivity 1,2 and CO 2 supply 2,5-7 , the genes encoding some of the main regulators of stomatal movements remain unknown. It has been proposed that guard cell anion channels function as important regulators of stomatal closure and are essential in mediating stomatal responses to physiological and stress stimuli 3,4,8 . However, the genes encoding membrane proteins that mediate guard cell anion efflux have not yet been identified. Here we report the mapping and characterization of an ozone-sensitive Arabidopsis thaliana mutant, slac1. We show that SLAC1 (SLOW ANION CHANNEL-ASSOCIATED 1) is preferentially expressed in guard cells and encodes a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins. The plasma membrane protein SLAC1 is essential for stomatal closure in response to CO 2 , ©2008 Nature Publishing GroupCorrespondence and requests for materials should be addressed to J.K. (jaakko.kangasjarvi@helsinki.fi). † Present address: Division of Biology, Imperial College London, London SW7 2AZ, UK. * These authors contributed equally to this work Fig. 3d and Supplementary Fig. 6a. N.N. performed experiments in Fig. 3a and Supplementary Fig. 7. Y.-F.W. performed experiments in Fig. 4 and Supplementary Figs 8 and 9. J.K. and J.I.S. wrote the paper. All the authors discussed the results, and commented on and edited the manuscript.The primary microarray data reported has been deposited with the ArrayExpress database under accession number E-MEXP-1388.Reprints and permissions information is available at www.nature.com/reprints. 8,11 by mediating anion efflux and causing membrane depolarization, which controls K + efflux through K + channels. So far, none of the candidates for plant anion channels -the plant homologues to the animal CLC chloride channels -has been localized to the plasma membrane 10 , and the first plant CLC channel that was functionally characterized encodes a central vacuolar proton/nitrate exchanger 12 , rather than an anion channel. Thus, despite their proposed importance in several physiological and stress responses in plants 8,10,11 , the molecular identity of the guard cell plasma membrane proteins that mediate anion channel activity has remained unknown. NIH Public AccessIn a mutant screen for O 3 sensitivity, a series of Arabidopsis ethyl methanesulphonate (EMS) mutants called radical-induced cell death (rcd) was identified 13,14 . One of them, a recessive mutant originally referred ...

A molecular pathway for CO2 response in Arabidopsis guard cells

“…Although several proteins have been shown to function in CO 2 -regulated stomatal response, some critical components are still missing 5,6,18 . Because membrane transporters play an important role in modulating stomatal response to external signals 5,6,[14][15][16][38][39][40] , we hypothesized that mutations in many of such transporters may affect stomatal responses to environmental signals including CO 2 concentration. We identified a large number of genes encoding potential solute transporters and collected T-DNA insertion mutants for these genes to compile a mutant library.…”

“…Elevated CO 2 concentration activates anion channels, resulting in depolarization of plasma membrane in guard cells, causing efflux of solutes and stomatal closure [7][8][9][10] . Earlier studies in Arabidopsis identified several mutants with defects in CO 2 -induced stomatal movements [11][12][13][14][15][16][17][18][19] . However, most of these mutants including abi1-1, abi2-1, gca2, ost1 and slac1 were insensitive to both CO 2 and abscisic acid (ABA), representing components shared by both signalling pathways 5,20 .…”

“…Activation of the slow (S-type) anion channels for anion efflux has been regarded as a critical step in stomatal closure 18,[21][22][23][24] . SLAC1 (Slow Anion ChannelAssociated 1) is a component of the S-type anion channel in Arabidopsis guard cells 14,15 . When expressed in Xenopus oocytes, SLAC1 forms a channel that is permeable to Cl À and NO 3 À , but not to HCO 3 À 23, 24 .…”

The role of vacuolar processing enzymes in plant immunity

“…The NtrbohD protein, 28 G protein-coupled receptors (GPCRs), 29 fast vacuolar (FV) channels, K + -selective vacuolar (VK) cation channels, 30 slow vacuolar (SV) channels, slow anion channel-associated 1 (SLAC1) 31,32 and H + -ATPases (AHA1 and AHA2) 33 are localized to the membrane and function during abiotic or biotic responses in guard cells. 34 These findings also demonstrate that the guard cell signal transduction in response to biotic and abiotic signals shares some common steps, including NO accumulation in guard cells.…”

The physiological, transcriptional and genetic responses of an ozone- sensitive and an ozone tolerant poplar and selected extremes of their F 2 progeny

“…Stomata regulate the entry of ozone into the leaf (Vahisalu et al, 2008), and when ozone reaches the apoplast, production of toxic reactive oxygen species (ROS) is initiated (Mahalingam et al, 2006;Wohlgemuth et al, 2002). Symptoms range from accelerated senescence (Karnosky et al, 1996) and a decrease in growth rate (Karnosky et al, 1996Wittig et al, 2009), to foliar injury manifested as necrotic lesions analogous to those formed during the hypersensitive response (HR) .…”