RRC ID 4046
Author Kovermann P, Meyer S, Hörtensteiner S, Picco C, Scholz-Starke J, Ravera S, Lee Y, Martinoia E.
Title The Arabidopsis vacuolar malate channel is a member of the ALMT family.
Journal Plant J
Abstract In plants, malate is a central metabolite and fulfills a large number of functions. Vacuolar malate may reach very high concentrations and fluctuate rapidly, whereas cytosolic malate is kept at a constant level allowing optimal metabolism. Recently, a vacuolar malate transporter (Arabidopsis thaliana tonoplast dicarboxylate transporter, AttDT) was identified that did not correspond to the well-characterized vacuolar malate channel. We therefore hypothesized that a member of the aluminum-activated malate transporter (ALMT) gene family could code for a vacuolar malate channel. Using GFP fusion constructs, we could show that AtALMT9 (A. thaliana ALMT9) is targeted to the vacuole. Promoter-GUS fusion constructs demonstrated that this gene is expressed in all organs, but is cell-type specific as GUS activity in leaves was detected nearly exclusively in mesophyll cells. Patch-clamp analysis of an Atalmt9 T-DNA insertion mutant exhibited strongly reduced vacuolar malate channel activity. In order to functionally characterize AtALMT9 as a malate channel, we heterologously expressed this gene in tobacco and in oocytes. Overexpression of AtALMT9-GFP in Nicotiana benthamiana leaves strongly enhanced the malate current densities across the mesophyll tonoplasts. Functional expression of AtALMT9 in Xenopus oocytes induced anion currents, which were clearly distinguishable from endogenous oocyte currents. Our results demonstrate that AtALMT9 is a vacuolar malate channel. Deletion mutants for AtALMT9 exhibit only slightly reduced malate content in mesophyll protoplasts and no visible phenotype, indicating that AttDT and the residual malate channel activity are sufficient to sustain the transport activity necessary to regulate the cytosolic malate homeostasis.
Volume 52(6)
Pages 1169-80
Published 2007-12-1
DOI 10.1111/j.1365-313X.2007.03367.x
PMID 18005230
MeSH Aluminum / metabolism Aluminum / pharmacology Animals Arabidopsis / genetics Arabidopsis / metabolism* Arabidopsis Proteins / genetics Arabidopsis Proteins / metabolism* Arabidopsis Proteins / physiology Biological Transport / drug effects Dicarboxylic Acid Transporters / genetics Dicarboxylic Acid Transporters / metabolism Dicarboxylic Acid Transporters / physiology Gene Expression Regulation, Plant Glucuronidase / genetics Glucuronidase / metabolism Green Fluorescent Proteins / genetics Green Fluorescent Proteins / metabolism Malates / metabolism* Membrane Potentials / physiology Mutation Oocytes / metabolism Oocytes / physiology Organic Anion Transporters / genetics Organic Anion Transporters / metabolism* Organic Anion Transporters / physiology Patch-Clamp Techniques Plants, Genetically Modified Recombinant Fusion Proteins / genetics Recombinant Fusion Proteins / metabolism Tobacco / genetics Tobacco / metabolism Vacuoles / metabolism* Xenopus
IF 6.141
Times Cited 144
Arabidopsis / Cultured plant cells, genes pda08640