Two tonoplast MATE proteins function as turgor-regulating chloride channels in Arabidopsis
Friday, 2017/03/10 | 07:38:07
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Haiwen Zhang, Fu-Geng Zhao, Ren-Jie Tang, Yuexuan Yu, Jiali Song, Yuan Wang, Legong Li, and Sheng Luan SignificanceTurgor pressure is the driving force for cell growth in plants, and the large central vacuole provides the major space for turgor regulation. However, the molecular identity and function of many transporters that control water and solute fluxes in and out of vacuoles remain unknown. We report here that two Multidrug and Toxic Compound Extrusion (MATE)-type transporters show previously unrecognized function as chloride channels essential for turgor regulation in Arabidopsis. The MATE transporters are highly conserved from bacteria, fungi, plants, to animals, and widely accepted as transporters of organic compounds. This study, showing some MATE transporters as chloride channels, thus breaks the old dogma on the functional definition of this large family of transporters. AbstractThe central vacuole in a plant cell occupies the majority of the cellular volume and plays a key role in turgor regulation. The vacuolar membrane (tonoplast) contains a large number of transporters that mediate fluxes of solutes and water, thereby adjusting cell turgor in response to developmental and environmental signals. We report that two tonoplast Detoxification efflux carrier (DTX)/Multidrug and Toxic Compound Extrusion (MATE) transporters, DTX33 and DTX35, function as chloride channels essential for turgor regulation in Arabidopsis. Ectopic expression of each transporter in Nicotiana benthamiana mesophyll cells elicited a large voltage-dependent inward chloride current across the tonoplast, showing that DTX33 and DTX35 each constitute a functional channel. Both channels are highly expressed in Arabidopsis tissues, including root hairs and guard cells that experience rapid turgor changes during root-hair elongation and stomatal movements. Disruption of these two genes, either in single or double mutants, resulted in shorter root hairs and smaller stomatal aperture, with double mutants showing more severe defects, suggesting that these two channels function additively to facilitate anion influx into the vacuole during cell expansion. In addition, dtx35 single mutant showed lower fertility as a result of a defect in pollen-tube growth. Indeed, patch-clamp recording of isolated vacuoles indicated that the inward chloride channel activity across the tonoplast was impaired in the double mutant. Because MATE proteins are widely known transporters of organic compounds, finding MATE members as chloride channels expands the functional definition of this large family of transporters.
See http://www.pnas.org/content/114/10/E2036.abstract.html?etoc PNAS March 7 2017; vol.114; no.10: E2036–E2045
Fig. 1. DTX33 and DTX35 are both tonoplast proteins. (A) Arabidopsis suspension culture cells were transiently transformed with 35S-DTX33::GFP, 35S-DTX35::GFP, or 35S-TPK1::GFP. (Left) GFP signals (green), (Center) bight field image of the same cell (DIC), and (Right) an overlay (GFP and DIC) of the same sample. (Scale bar: 5 μM.) (B) Transgenic Arabidopsis plants expressing 35S:DTX33-GFP and 35S:DTX35-GFP. (Left) GFP signals (green), (Center) the plasma membrane stained with FM4-64 (red), and (Right) an overlay (green and red) from the same sample. (Scale bar: 20 μM.) (C) Vacuoles released from Arabidopsis mesophyll protoplasts that were transiently transformed with 35S-DTX33::GFP and 35S-DTX35::GFP. (Scale bar: 5 μM.) |
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