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CELL BIOLOGY AND SIGNAL TRANSDUCTION

AtOPT6 Transports Glutathione Derivatives and Is Induced by Primisulfuron¹

Unité Mixte de Recherches, Centre National de la Recherche Scientifique 6161, Transport des Assimilats, Laboratoire de Physiologie, Biochimie et Biologie Moléculaire Végétales, Bâtiment Botanique, Unité de Formation et de Recherche Sciences Fondamentales et Appliquées, 86022 Poitiers Cédex, France

The oligopeptide transporter (OPT) family contains nine members in Arabidopsis. While there is some evidence that AtOPTs mediate the uptake of tetra- and pentapeptides, OPT homologs in rice (Oryza sativa; OsGT1) and Indian mustard (Brassica juncea; BjGT1) have been described as transporters of glutathione derivatives. This study investigates the possibility that two members of the AtOPT family, AtOPT6 and AtOPT7, may also transport glutathione and its conjugates. Complementation of the hgt1met1 yeast double mutant by plant homologs of the yeast glutathione transporter HGT1 (AtOPT6, AtOPT7, OsGT1, BjGT1) did not restore the growth phenotype, unlike complementation by HGT1. By contrast, complementation by AtOPT6 restored growth of the hgt1 yeast mutant on a medium containing reduced (GSH) or oxidized glutathione as the sole sulfur source and induced uptake of [³H]GSH, whereas complementation by AtOPT7 did not. In these conditions, AtOPT6-dependent GSH uptake in yeast was mediated by a high affinity (K_m = 400 µM) and a low affinity (K_m = 5 mM) phase. It was strongly competed for by an excess oxidized glutathione and glutathione-N-ethylmaleimide conjugate. Growth assays of yeasts in the presence of cadmium (Cd) suggested that AtOPT6 may transport Cd and Cd/GSH conjugate. Reporter gene experiments showed that AtOPT6 is mainly expressed in dividing areas of the plant (cambium, areas of lateral root initiation). RNA blots on cell suspensions and real-time reverse transcription-PCR on Arabidopsis plants indicated that AtOPT6 expression is strongly induced by primisulfuron and, to a lesser extent, by abscisic acid but not by Cd. Altogether, the data show that the substrate specificity and the physiological functions of AtOPT members may be diverse. In addition to peptide transport, AtOPT6 is able to transport glutathione derivatives and metal complexes, and may be involved in stress resistance.

² Present address: Chinese Academy of Sciences, Plant Physiology Laboratory, Botanical Institute of South China, 510650 Leyigu Guangzhou, China.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.039859.

^* Corresponding author; e-mail serge.delrot{at}univ-poitiers.fr; fax 33 (0)5 49 45 41 86.

Received January 28, 2004; returned for revision April 8, 2004; accepted April 13, 2004.

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