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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

A Genetic Screen for Nitrate Regulatory Mutants Captures the Nitrate Transporter Gene NRT1.1^1,[W],[OA]

Section of Cell and Developmental Biology, Division of Biological Sciences, University of California at San Diego, La Jolla, California 92093–0116

Nitrate regulatory mutants (nrg) of Arabidopsis (Arabidopsis thaliana) were sought using a genetic screen that employed a nitrate-inducible promoter fused to the yellow fluorescent protein marker gene YFP. A mutation was identified that impaired nitrate induction, and it was localized to the nitrate regulatory gene NLP7, demonstrating the validity of this screen. A second, independent mutation (nrg1) mapped to a region containing the NRT1.1 (CHL1) nitrate transporter gene on chromosome 1. Sequence analysis of NRT1.1 in the mutant revealed a nonsense mutation that truncated the NRT1.1 protein at amino acid 301. The nrg1 mutation disrupted nitrate regulation of several endogenous genes as induction of three nitrate-responsive genes (NIA1, NiR, and NRT2.1) was dramatically reduced in roots of the mutant after 2-h treatment using nitrate concentrations from 0.25 to 20 mM. Another nrt1.1 mutant (deletion mutant chl1-5) showed a similar phenotype. The loss of nitrate induction in the two nrt1.1 mutants (nrg1 and chl1-5) was not explained by reduced nitrate uptake and was reversed by nitrogen deprivation. Microarray analysis showed that nitrate induction of 111 genes was reduced and of three genes increased 2-fold or more in the nrg1 mutant. Genes involved in nitrate assimilation, energy metabolism, and pentose-phosphate pathway were most affected. These results strongly support the model that NRT1.1 acts as a nitrate regulator or sensor in Arabidopsis.

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: Nigel M. Crawford (ncrawford{at}ucsd.edu).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.140434

^* Corresponding author; e-mail ncrawford{at}ucsd.edu.

Received April 28, 2009; accepted July 15, 2009; published July 24, 2009.

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On the Inside

Peter V. Minorsky
Plant Physiol. 2009 151: 1-2. [Full Text]