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- 저자 : Scholz-Starke, Joachim (검색결과 1 건)
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The Arabidopsis vacuolar malate channel is a member of the ALMT family
Kovermann, Peter,Meyer, Stefan,Hö,rtensteiner, Stefan,Picco, Cristiana,Scholz-Starke, Joachim,Ravera, Silvia,Lee, Youngsook,Martinoia, Enrico Blackwell Publishing Ltd 2007 The Plant journal Vol.52 No.6
<P>Summary</P><P>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 (<I>Arabidopsis thaliana</I> tonoplast dicarboxylate transporter, <I>At</I>tDT) 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 <I>At</I>ALMT9 (<I>A. thaliana</I> 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 <I>Atalmt9</I> T-DNA insertion mutant exhibited strongly reduced vacuolar malate channel activity. In order to functionally characterize <I>At</I>ALMT9 as a malate channel, we heterologously expressed this gene in tobacco and in oocytes. Overexpression of <I>At</I>ALMT9-GFP in <I>Nicotiana benthamiana</I> leaves strongly enhanced the malate current densities across the mesophyll tonoplasts. Functional expression of <I>At</I>ALMT9 in <I>Xenopus</I> oocytes induced anion currents, which were clearly distinguishable from endogenous oocyte currents. Our results demonstrate that <I>At</I>ALMT9 is a vacuolar malate channel. Deletion mutants for <I>At</I>ALMT9 exhibit only slightly reduced malate content in mesophyll protoplasts and no visible phenotype, indicating that <I>At</I>tDT and the residual malate channel activity are sufficient to sustain the transport activity necessary to regulate the cytosolic malate homeostasis.</P>
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