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Plant Physiol, February 2000, Vol. 122, pp. 379-388
Cloning and Functional Characterization of a Constitutively
Expressed Nitrate Transporter Gene, OsNRT1, from
Rice1
Chung-Ming
Lin,
Serry
Koh,
Gary
Stacey,
Su-May
Yu,
Tsai-Yun
Lin, and
Yi-Fang
Tsay*
Department of Life Science, School of Life Science, National Tsing
Hua University, 30043, Hsin-Chu, Taiwan (C.-M.L., T.-Y.L.); Institute
of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan (C.-M.L.,
S.-M.Y., Y.-F.T.); and Department of Microbiology and Center
for Legume Research, University of Tennessee, Knoxville, Tennessee
37996-0845 (S.K., G.S.).
Elucidating how rice (Oryza
sativa) takes up nitrate at the molecular level could help
improve the low recovery rate (<50%) of nitrogen fertilizer in rice
paddies. As a first step toward that goal, we have cloned a nitrate
transporter gene from rice called OsNRT1. OsNRT1 is a
new member of a growing transporter family called PTR, which consists
not only of nitrate transporters from higher plants that are homologs
of the Arabidopsis CHL1 (AtNRT1) protein, but also peptide transporters
from a wide variety of genera including animals, plants, fungi, and
bacteria. However, despite the fact that OsNRT1 shares a higher degree
of sequence identity with the two peptide transporters from plants
(approximately 50%) than with the nitrate transporters (approximately
40%) of the PTR family, no peptide transport activity was observed
when OsNRT1 was expressed in either Xenopus oocytes or
yeast. Furthermore, contrasting the dual-affinity nitrate transport
activity of CHL1, OsNRT1 displayed only low-affinity nitrate transport
activity in Xenopus oocytes, with a
Km value of approximately 9 mM.
Northern-blot and in situ hybridization analysis indicated that OsNRT1
is constitutively expressed in the most external layer of the root,
epidermis and root hair. These data strongly indicate that
OsNRT1 encodes a constitutive component of a
low-affinity nitrate uptake system for rice.
1
This work was supported by the biotechnology
program of the Academia Sinica, Taipei, Taiwan (grant nos. BT-85-06,
BT-86-03, and IBAS-87-01 to Y.F.T.), and by the Biomedical Research
Foundation, Taipei, Taiwan. Work performed in the laboratory of G.S.
was supported by the National Research Initiative Competitive Grants
Program, U.S. Department of Agriculture (grant no. 99-35304-8194).
*
Corresponding author; e-mail mbyftsay{at}ccvax.sinica.edu.tw; fax
886-2-2782-6085.
© 2000 American Society of Plant Physiologists
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