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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Characterization of a Selenate-Resistant Arabidopsis Mutant. Root Growth as a Potential Target for Selenate Toxicity^1,[OA]

Laboratoire de Biochimie et Physiologie Moléculaire des Plantes, Ecole Nationale Supérieure Agronomique de Montpellier, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Montpellier II, 34060 Montpellier, France (E.E.K., N.C., H.R., P.F., P.B., J.-C.D.); and Department of Plant and Microbial Biology, University of California, Berkeley, California 94720–3102 (N.T.)

Screening an Arabidopsis (Arabidopsis thaliana) T-DNA mutant library for selenate resistance enabled us to isolate a selenate-resistant mutant line (sel1-11). Molecular and genetic characterization showed that the mutant contained a lesion in the SULTR1;2 gene that encodes a high affinity root sulfate transporter. We showed that SULTR1;2 is the only gene among 13 mutated genes of the Arabidopsis sulfate transporter family whose mutation conferred selenate resistance to Arabidopsis. The selenate resistance phenotype of the sel1-11 mutant was mirrored by an 8-fold increase of root growth in the presence of selenate as shown by the calculated lethal concentration values. The impairment of SULTR1;2 activity in sel1-11 resulted in a reduced ³⁵S-sulfate uptake capacity by both roots and calli and a reduced sulfate and selenate content in root, shoot, and calli. Comparing sulfate-to-selenate ratios instead of absolute sulfate and selenate contents in roots and shoots enabled us to gain better insight into the mechanism of selenate toxicity in Arabidopsis. Roots of the sel1-11 mutant line showed a higher sulfate to selenate ratio than that of wild-type roots, while there were no significant differences in sulfate to selenate ratios in shoots of wild-type and mutant lines. These results indicated that the mechanism that confers the selenate resistance phenotype to the sel1-11 line takes place rather in the roots. It might be in part the result of a lower selenate uptake and of a protective effect of sulfate against the toxic effects of selenate on root growth. These results revealed in plants a central and specific role of the transporter SULTR1;2 in selenate sensitivity; they further suggested that root growth and potentially the root tip activity might be a specific target of selenate toxicity in Arabidopsis.

² Present address: Center for Rhizosphere Biology, Department of Horticulture, Colorado State University, Fort Collins, CO 80523–1173.

³ Present address: Laboratoire de Biotechnologie des Plantes, Université de Lausanne, CH–1015 Lausanne, Switzerland.

The author responsible for distribution of materials integral to the findings presented in this article in accord with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jean-Claude Davidian (davidian{at}supagro.inra.fr).

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.091462

^* Corresponding author; e-mail davidian{at}supagro.inra.fr; fax 33–0467525737.

Received October 18, 2006; accepted December 26, 2006; published January 5, 2007.

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