Arabidopsis GTG1 functions as an anion channel regulating endomembrane pH

Dorey, Adam, Adam, Ilectra, Wong, Nancy, O'kelly, Ita, de Planque, Maurits R.R., Terry, Matthew J. and Williams, Lorraine E. (2018) Arabidopsis GTG1 functions as an anion channel regulating endomembrane pH. Plant Biology 2018, , Montreal, Canada. 14 - 18 Jul 2018.

Abstract

The G-protein coupled receptor type G proteins/Golgi pH regulator proteins (GTG/ GPHRs) are a family of membrane proteins found in eukaryotes with diverse functions proposed. These include functioning as an ABA receptor1 (Arabidopsis), an endomembrane protein involved in growth and development2 (Arabidopsis), a calcium channel for cold perception3 (rice) or as an anion channel regulating Golgi pH4 (Chinese hamster). Here we use model organisms, Arabidopsis thaliana and Caenorhabditis elegans, to reveal a conserved function across kingdoms for these proteins as a novel family of anion channels. Both organisms contain two genes (AtGTG1, AtGTG2, Cel-GPHR-1, Cel-GPHR-2) that act redundantly and knocking out both results in defects in growth and development. We demonstrate a conserved function, with Cel-GPHR-1 rescuing the root and hypocotyl defects observed in the Arabidopsis gtg1gtg2 double mutant. Both AtGTG1 and Cel-GPHR-1 localize to the ER and Golgi when expressed stably in Arabidopsis and transiently in tobacco. Patch-clamp studies reveal that AtGTG1 and Cel-GPHR-1 exhibit anion-specific channel activity when expressed in a mammalian cell line (HEK-293) and the AtGTG1-dependent Cl- current is inhibited by the anion channel blocker 4,4-diisothiocyanatostilbene-2,2-disulfonic acid (DIDS). Furthermore, anion channel activity is confirmed when AtGTG1 is reconstituted in a planar lipid bilayer. By targeting the pH sensor pHluorin to different endomembrane compartments in Arabidopsis, we demonstrate a physiological role for AtGTG1 in regulating ER and Golgi pH. Overall, this study demonstrates a fundamental conserved function of the GTG/GPHRs as anion channels providing counter-ion conductance for regulating endomembrane pH.

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Contributors

Author: Maurits R.R. de Planque

Author: Matthew J. Terry

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