Journal Article

<i>In planta</i> regulation of the <i>Arabidopsis</i> Ca<sup>2+</sup>/H<sup>+</sup> antiporter CAX1

Hui Mei, Jian Zhao, Jon K. Pittman, Jinesh Lachmansingh, Sunghun Park and Kendal D. Hirschi

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 58, issue 12, pages 3419-3427
Published in print September 2007 | ISSN: 0022-0957
Published online September 2007 | e-ISSN: 1460-2431 | DOI: https://dx.doi.org/10.1093/jxb/erm190

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Vacuolar localized Ca2+/H+ exchangers such as Arabidopsis thaliana cation exchanger 1 (CAX1) play important roles in Ca2+ homeostasis. When expressed in yeast, CAX1 is regulated via an N-terminal autoinhibitory domain. In yeast expression assays, a 36 amino acid N-terminal truncation of CAX1, termed sCAX1, and variants with specific mutations in this N-terminus, show CAX1-mediated Ca2+/H+ antiport activity. Furthermore, transgenic plants expressing sCAX1 display increased Ca2+ accumulation and heightened activity of vacuolar Ca2+/H+ antiport. Here the properties of N-terminal CAX1 variants in plants and yeast expression systems are compared and contrasted to determine if autoinhibition of CAX1 is occurring in planta. Initially, using ionome analysis, it has been demonstrated that only yeast cells expressing activated CAX1 transporters have altered total calcium content and fluctuations in zinc and nickel. Tobacco plants expressing activated CAX1 variants displayed hypersensitivity to ion imbalances, increased calcium accumulation, heightened concentrations of other mineral nutrients such as potassium, magnesium and manganese, and increased activity of tonoplast-enriched Ca2+/H+ transport. Despite high in planta gene expression, CAX1 and N-terminal variants of CAX1 which were not active in yeast, displayed none of the aforementioned phenotypes. Although several plant transporters appear to contain N-terminal autoinhibitory domains, this work is the first to document clearly N-terminal-dependent regulation of a Ca2+ transporter in transgenic plants. Engineering the autoinhibitory domain thus provides a strategy to enhance transport function to affect agronomic traits.

Keywords: Arabidopsis; autoinhibition; calcium; ionome; tobacco; transport

Journal Article.  5607 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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