Plant Molecular Biology 40: 883–892, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
Regulation of the hvst1 gene encoding a high-afﬁnity sulfate transporter
from Hordeum vulgare
Joseph John Vidmar
, Jan. K. Schjoerring
, Bruno Touraine
and Anthony D.M. Glass
Department of Botany, University of British Columbia, 6270 University Blvd, Vancouver, British Columbia,
Canada, V6T 1Z4 (
author for correspondence);
Plant Nutrition Laboratory, Department of Agricultural
Sciences, Royal Veterinary and Agricultural University, Thorvaldsensvej 40, 1871 Frederiksberg C, Copenhagen,
Biochimie et Mol´eculaire Physiologie des Plantes, Ecole Nationale Sup´erieure d’Agronomique de
Monpellier/Institut National de la Recherche Agronomique/Centre National de la Recherche Scientiﬁque, Unit´ede
Recherche Associ´ee 2133, 34060 Montpellier Cedex 1, France
Received 11 October 1998; accepted in revised form 20 May 1999
Key words: co-regulation, Hordeum vulgare, nitrogen assimilation, sulfate transporter, sulfur assimilation
A cDNA, hvst1, was isolated from Hordeum vulgare by heterologous complementation in Escherichia coli.This
cDNA encodes a high-afﬁnity sulfate transporter that is 2442 bp in length and consists of 660 amino acids.
Under steady-state conditions of sulfate supply during culture, sulfate inﬂux (measured at 100 µM external
sulfate concentration) and hvst1 transcript level were inversely correlated with sulfate concentrations in the culture
solution. Glutathione (GSH) concentrations increased as external sulfate was increased from 2.5 to 250 µM. A
time-course study, designed to investigate effects of sulfate withdrawal on the abundance of hvst1 transcript,
showed a 5-fold increase of the latter within the ﬁrst two hours. This was followed by a further slight increase during
the next 46 h. These changes were accompanied by a parallel increase in sulfate inﬂux and a decrease of root GSH
concentrations. When plants that had been deprived of sulfate for 24 h were exposedto L-cysteine (Cys) or GSH for
3 h, GSH was the more effective down-regulator, reducing hvst1 transcript level to below that of unstarved controls.
The decrease in transcript abundance induced by sulfate or Cys was partially relieved by the addition of buthionine
sulfoximine (BSO), an inhibitor of GSH synthesis. Both hvst1 transcripts and sulfate inﬂux increased as a function
of N supply to N-starved plants. Amino oxyacetate acid (AOA), an aminotransferase inhibitor, when supplied
, increased transcript abundance of hvst1, while tungstate, methionine sulfoximine (MSO) and azaserine
(AZA), inhibitors of nitrate reductase, glutamine synthetase and glutamate synthase (GOGAT), respectively, were
without effect. AOA decreased root concentrations of aspartate (Asp), Cys and GSH; in contrast, glutamate (Glu)
concentrations remained unchanged.
The transport of sulfate (SO
) across the plasma
membranes of root cells is thought to be an active
process driven by proton motive force, through a
symporter (Laas and Ullrich-Eberius, 1984;
Clarkson et al., 1993; Hawkesford et al., 1993).
Transport is mediated by at least two transport sys-
The nucleotide sequence data reported will appear in the
EMBL, GenBank and DDBJ Nucleotide Sequence Databases under
the accession number U52867.
tems, referred to as high- and low-afﬁnity transport
systems, respectively (Datko and Mudd, 1984; Laas
and Ullrich-Eberius, 1984; Hawkesford et al., 1993).
In most organisms, and including higher plants, the
absorption and assimilation of sulfur (typically as sul-
fate) is highly regulated. The withdrawal of SO
from the external environment causes sulfate transport
to be up-regulated (Clarkson et al., 1983; Hawkesford
and Belcher, 1991). This regulation is considered to
be mediated by negative feedback control, in which
sulfate or products of sulfate assimilation such as Cys,