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First published online January 13, 2006; 10.1104/pp.105.074385 Plant Physiology 140:1036-1046 (2006) © 2006 American Society of Plant Biologists High-Affinity Nitrate Transport in Roots of Arabidopsis Depends on Expression of the NAR2-Like Gene AtNRT3.11Section of Cell and Developmental Biology, Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093–0116 (M.O., N.M.C.); and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 (A.K., W.L., Y.W., M.Y.S., A.D.M.G.)
The NAR2 protein of Chlamydomonas reinhardtii has no known transport activity yet it is required for high-affinity nitrate uptake. Arabidopsis (Arabidopsis thaliana) possesses two genes, AtNRT3.1 and AtNRT3.2, that are similar to the C. reinhardtii NAR2 gene. AtNRT3.1 accounts for greater than 99% of NRT3 mRNA and is induced 6-fold by nitrate. AtNRT3.2 was expressed constitutively at a very low level and did not compensate for the loss of AtNRT3.1 in two Atnrt3.1 mutants. Nitrate uptake by roots and nitrate induction of gene expression were analyzed in two T-DNA mutants, Atnrt3.1-1 and Atnrt3.1-2, disrupted in the AtNRT3.1 promoter and coding regions, respectively, in 5-week-old plants. Nitrate induction of the nitrate transporter genes AtNRT1.1 and AtNRT2.1 was reduced in Atnrt3.1 mutant plants, and this reduced expression was correlated with reduced nitrate concentrations in the tissues. Constitutive high-affinity influx was reduced by 34% and 89%, respectively, in Atnrt3.1-1 and Atnrt3.1-2 mutant plants, while high-affinity nitrate-inducible influx was reduced by 92% and 96%, respectively, following induction with 1 mM KNO3 after 7 d of nitrogen deprivation. By contrast, low-affinity influx appeared to be unaffected. Thus, the constitutive high-affinity influx and nitrate-inducible high-affinity influx (but not the low-affinity influx) of higher plant roots require a functional AtNRT3 (NAR2) gene.
1 This work was supported by the Natural Sciences and Engineering Research Council of Canada (to A.D.M.G) and by the National Institutes of Health (grant no. GM40672 to N.M.C.). 2 Present address: Department of Biology, Colorado State University, Fort Collins, CO 80525. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Anthony D.M. Glass (aglass{at}interchange.ubc.ca). Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.074385. * Corresponding author; e-mail aglass{at}interchange.ubc.ca; fax 604–822–6089. Received November 18, 2005; returned for revision January 3, 2006; accepted January 9, 2006. Related articles in Plant Physiol.:
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