A Putative Role for the Vacuolar Calcium/Manganese Proton Antiporter AtCAX2 in Heavy Metal Detoxification

G. Schaaf; E. Catoni; M. Fitz; R. Schwacke; A. Schneider; N. von Wirén; W. B. Frommer

doi:10.1055/s-2002-35432

Plant Biology, Table of Contents

Plant Biol (Stuttg) 2002; 4(5): 612-618
DOI: 10.1055/s-2002-35432

Original Paper

Georg Thieme Verlag Stuttgart ·New York

A Putative Role for the Vacuolar Calcium/Manganese Proton Antiporter AtCAX2 in Heavy Metal Detoxification

G. Schaaf ^1,4 , E. Catoni ^2,4 , M. Fitz ² , R. Schwacke ³ , A. Schneider ³ , N. von Wirén ¹ , W. B. Frommer ²

¹ Plant Nutrition, University of Hohenheim, Stuttgart, Germany
² ZMBP, Plant Physiology, University of Tübingen, Tübingen, Germany
³ Institut für Botanik, University of Cologne, Cologne, Germany
⁴ both authors contributed equally to this manuscript

Abstract

Regulation of uptake and compartmentation of metal ions is important for the maintenance of metal ion homeostasis. To identify mechanisms involved in the protection of plants from Mn toxicity, wild-type yeast was transformed with an Arabidopsis cDNA library and transformants were screened on toxic Mn concentrations. Wild-type yeast could not grow in the presence of 30 mM MnSO₄, while two transformants carrying variants of the same gene were able to grow. Database searches revealed that the isolated cDNAs correspond to AtCAX2, previously described as a vacuolar calcium-proton antiporter. Since no other genes could be identified, AtCAX2 might represent a major function permitting Mn detoxification in this suppressor screen. Furthermore, yeast transformed with the two AtCAX2 cDNAs showed increased sensitivity towards hydrogen peroxide, pointing to a limited availability of cytoplasmic Mn in the presence of AtCAX2 activity. The open reading frames of the cDNA encoded polypeptides that have a 42 and a 92 amino acids shorter N-terminal region relative to the predicted full-length coding region of AtCAX2. In contrast to both truncated cDNAs, the full-length clone was unable to confer Mn resistance to yeast, indicating that, similar to AtCAX1, AtCAX2 also carries an autoinhibitory N-terminal domain regulating the activity of AtCAX2.

Abbreviations

aa: amino acid

AtCAX1, AtCAX2: Arabidopsis cDNAs (genes) encoding Ca²⁺ exchangers 1 and 2, respectively

EST: expressed sequence tag

5-FOA: 5-fluoroorotic acid

PGK: phosphoglycerol kinase

TMD: transmembrane spanning domain

Key words

Manganese toxicity - vacuolar transporter - Arabidopsis thaliana - autoinhibitory domain - reactive oxygen species (ROS)

Full Text

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W. B. Frommer

ZMBP
Eberhard-Karls-Universität Tübingen

72076 Tübingen
Germany

Email: wbf@zmbp.uni-tuebingen.de

Section Editor: H. Rennenberg