Disruption of a Gene Encoding C4-Dicarboxylate Transporter-Like Protein Increases Ozone Sensitivity Through Deregulation of the Stomatal Response in Arabidopsis thaliana

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895

In response to drought stress the phytohormone ABA (abscisic acid) induces stomatal closure and, therein, activates guard cell anion channels in a calcium-dependent as well as-independent manner. Two key components of the ABA signaling pathway are the protein kinase OST1 (open stomata 1) and the protein phosphatase ABI1 (ABA insensitive 1). The recently identified guard cell anion channel SLAC1 appeared to be the key ion channel in this signaling pathway but remained electrically silent when expressed heterologously. Using split YFP assays, we identified OST1 as an interaction partner of SLAC1 and ABI1. Upon coexpression of SLAC1 with OST1 in Xenopus oocytes, SLAC1-related anion currents appeared similar to those observed in guard cells. Integration of ABI1 into the SLAC1/OST1 complex, however, prevented SLAC1 activation. Our studies demonstrate that SLAC1 represents the slow, deactivating, weak voltage-dependent anion channel of guard cells controlled by phosphorylation/dephosphorylation.ABA signaling ͉ S-type anion channel ͉ OST1/ABI1

Section: Resultsmentioning

confidence: 99%

Activity of guard cell anion channel SLAC1 is controlled by drought-stress signaling kinase-phosphatase pair

Geiger

Scherzer²,

Mumm³

et al. 2009

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895

“…Recently, SLAC1, a guard cell anion channel, was identified (3)(4)(5). In guard cells of these ABA-and CO 2 /O 3 -insensitive mutant plants, anion currents appeared largely suppressed.…”

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confidence: 99%

Guard cell anion channel SLAC1 is regulated by CDPK protein kinases with distinct Ca ²⁺ affinities

Geiger¹,

Scherzer²,

Mumm³

et al. 2010

496

563

In response to drought stress, the phytohormone abscisic acid (ABA) induces stomatal closure. Thereby the stress hormone activates guard cell anion channels in a calcium-dependent, as well as -independent, manner. Open stomata 1 protein kinase (OST1) and ABI1 protein phosphatase (ABA insensitive 1) represent key components of calcium-independent ABA signaling. Recently, the guard cell anion channel SLAC1 was identified. When expressed heterologously SLAC1 remained electrically silent. Upon coexpression with Ca 2+ -independent OST1, however, SLAC1 anion channels appear activated in an ABI1-dependent manner. Mutants lacking distinct calcium-dependent protein kinases (CPKs) appeared impaired in ABA stimulation of guard cell ion channels, too. To study SLAC1 activation via the calcium-dependent ABA pathway, we studied the SLAC1 response to CPKs in the Xenopus laevis oocyte system. Split YFP-based protein-protein interaction assays, using SLAC1 as the bait, identified guard cell expressed CPK21 and 23 as major interacting partners. Upon coexpression of SLAC1 with CPK21 and 23, anion currents document SLAC1 stimulation by these guard cell protein kinases. Ca 2+ -sensitive activation of SLAC1, however, could be assigned to the CPK21 pathway only because CPK23 turned out to be rather Ca 2+ -insensitive. In line with activation by OST1, CPK activation of the guard cell anion channel was suppressed by ABI1. Thus the CPK and OST1 branch of ABA signal transduction in guard cells seem to converge on the level of SLAC1 under the control of the ABI1/ABA-receptor complex.abscisic acid signaling | drought stress | guard cell | S-type anion channel T he drought hormone abscisic acid (ABA) triggers release of K + and anions from guard cells and thereby causes stomatal closure (1, 2). Recently, SLAC1, a guard cell anion channel, was identified (3-5). In guard cells of these ABA-and CO 2 /O 3 -insensitive mutant plants, anion currents appeared largely suppressed. When SLAC1 was expressed with the open stomata 1 protein kinase (OST1) in Xenopus oocytes, SLAC1-related anion currents, similar to those observed in guard cells, appeared (6). The presence of ABI1, however, prevented SLAC1 activation. This ABA pathway resembles the Ca 2+ -independent activation of SLAC-type anion currents in guard cells. ABA signal transduction, however, has been shown to activate guard cell anion channels in a calcium-independent as well as -dependent manner (7-10). This became evident in abi1-1 mutant plants, where anion channels do not respond to ABA anymore (11) but still activate with calcium (12). Furthermore the described mutant growth controlled by abscisic acid (gca2) (13-14), isolated from the Arabidopsis ecotype Landsberg erecta, was shown to be impaired in ABA-induced stomatal closure in a Ca 2+ -dependent manner. Moreover [Ca 2+ ] cyt elevation was shown to result in activation of S-type anion channels via phosphorylation (12, 15), suggesting a role of phosphorylation events in [Ca 2+ ] cyt signaling.CDPKs resemble Ca 2+ -dependent Ser/Thr pr...

“…High concentrations of ozone induce oxidative stress, which activates programmed cell death and significantly inhibits plant growth, causing crop losses estimated to be in the billions of dollars (2,3). To study the mechanisms of ozone damage in plants, researchers have isolated Arabidopsis thaliana mutants that exhibit hypersensitivity to ozone exposure (4), including several mutants with higher stomatal conductance than wild type (WT), such as radicalinduced cell death1 (rcd1), rcd2, and ozone sensitive1/slow anion channel-associated1 (ozs1/slac1) (5)(6)(7)(8). In addition, the Arabidopsis ecotype Cvi-0, which has higher stomatal conductance than other ecotypes, also exhibits hypersensitivity to ozone compared with other ecotypes (9,10).…”

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confidence: 99%

“…Hyperpolarization of the plasma membrane caused by the H + -ATPases promotes stomatal opening through activation of the voltage-gated K + inward-rectifying channels (K + in ), encoded by K + CHANNEL IN ARABIDOPSIS THALIANA1 (KAT1), KAT2, and ARABIDOPSIS K TRANSPORTER 1 (AKT1), which induce water entry into guard cells (11,12). By contrast, depolarization of the plasma membrane activates outward-rectifying K + channels (6)(7)(8), which induce water efflux from guard cells, resulting in stomatal closure (11,12).…”

mentioning

confidence: 99%

GOLDEN 2-LIKE transcription factors for chloroplast development affect ozone tolerance through the regulation of stomatal movement

Nagatoshi

Mitsuda

Hayashi

et al. 2016

Stomatal movements regulate gas exchange, thus directly affecting the efficiency of photosynthesis and the sensitivity of plants to air pollutants such as ozone. The GARP family transcription factors GOLDEN 2-LIKE1 (GLK1) and GLK2 have known functions in chloroplast development. Here, we show that Arabidopsis thaliana (A. thaliana) plants expressing the chimeric repressors for GLK1 and -2 (GLK1/2-SRDX) exhibited a closed-stomata phenotype and strong tolerance to ozone. By contrast, plants that overexpress GLK1/2 exhibited an open-stomata phenotype and higher sensitivity to ozone. The plants expressing GLK1-SRDX had reduced expression of the genes for inwardly rectifying K + (K + in ) channels and reduced K + in channel activity. Abscisic acid treatment did not affect the stomatal phenotype of 35S:GLK1/2-SRDX plants or the transcriptional activity for K + in channel gene, indicating that GLK1/2 act independently of abscisic acid signaling. Our results indicate that GLK1/2 positively regulate the expression of genes for K + in channels and promote stomatal opening. Because the chimeric GLK1-SRDX repressor driven by a guard cell-specific promoter induced a closed-stomata phenotype without affecting chloroplast development in mesophyll cells, modulating GLK1/2 activity may provide an effective tool to control stomatal movements and thus to confer resistance to air pollutants.