Identification of the Arabidopsis CHL3 Gene as the Nitrate Reductase Structural Gene NIA2

Abstract

Chlorate, the chlorine analog of nitrate, is a herbicide that has been used to select mutants impaired in the process of nitrate assimilation. In Arabidopsis thaliana, mutations at any one of eight distinct loci confer resistance to chlorate. The molecular identities of the genes at these loci are not known; however, one of these loci-chI3-maps very near the nitrate reductase structural gene NIA2. Through the isolation, characterization, and genetic analysis of new chlorate-resistant mutants generated by gamma irradiation, we have been able to demonstrate that the CHL3 gene and the NIA2 gene are identical. Three new chlorate-resistant mutants were identified that had deletions of the entire NIA2 gene. These nia2 null mutants were viable and still retained 10% of wild-type nitrate reductase activity in the leaves of the plants. All three deletion mutations were found to be new alleles of chI3. lntroduction of the NIA2 gene back into these ch13 mutants by Agrobacterium-mediated transformation partially complemented their mutant phenotype. From these data, we conclude that Arabidopsis has at least two functional nitrate reductase genes and that the NIA2 gene product accounts for the majority of the leaf nitrate reductase activity and chlorate sensitivity of Arabidopsis plants.

Environmental Nitrate Stimulates Abscisic Acid Accumulation in Arabidopsis Root Tips by Releasing It from Inactive Stores

“…We measured the expression of a set of three ABA-responsive genes, ABA-INSENSITIVE5 (ABI5) (Finkelstein and Lynch, 2000), RESPONSIVE TO ABA18 (RAB18) (Kim et al, 2011), and RESPONSIVE TO DESSICATION29A (RD29A) (Yamaguchi-Shinozaki and Shinozaki, 1993); three NO 3 2 -inducible genes, NITRATE REDUCTASE1 (NIA1) (Parinov et al, 1999), NIA2 (Wilkinson and Crawford, 1991), and NITRITE REDUCTASE1 (NIR1) (Hwang et al, 1997); the ABA biosynthesis gene ABA DEFICIENT2 (ABA2) (Léon-Kloosterziel et al, 1996); and ABA deconjugation enzyme BG2 (Xu et al, 2012; Figure 4P) in (A) ABA immunofluorescence intensity plotted as a percentage of intensity in control roots or roots treated for 2 d with either KCl, ABA, or KNO 3 . Fluorescence intensity was measured as the sum of total fluorescence of the transverse or vertical line scans of treated and untreated roots (n = 10 roots for each column).…”

Functional Assessment of the Medicago truncatula NIP/LATD Protein Demonstrates That It Is a High-Affinity Nitrate Transporter

“…Three days after ClO 3 2 treatment, plants were switched to irrigation medium lacking ClO 3 2 and NO 3 2 . Plants were examined 7 to 10 d after ClO 3 2 treatment for necrosis and bleaching symptoms characteristic of chlorate toxicity (Wilkinson and Crawford, 1991), and their fresh weights and chlorophyll contents were obtained. Digital color photographs of the plants were obtained, corrected for color balance (Supplemental Fig.…”

Identification of Arabidopsis Mutants Impaired in the Systemic Regulation of Root Nitrate Uptake by the Nitrogen Status of the Plant

“…These included NAR2.1(NRT3.1), encoding a protein required for NRT2.1-mediated transport activity (Orsel et al, 2006), NRT2.2 and NRT1.1, which encode NO 3 2 transporters involved in root NO 3 2 uptake (Tsay et al, 1993, Li et al, 2007, NIA1 and NIA2, encoding the two isoforms of the nitrate reductase apoprotein (Cheng et al, 1988, Wilkinson and Crawford, 1991, and AMT1.1, AMT1.2, and AMT1.3, encoding NH 4 + transporters contributing to root NH 4 + uptake (Loque et al, 2006, Yuan et al, 2007. NAR2.1 has been reported to be regulated similarly to NRT2.1 (Krouk et al, 2006;Okamoto et al, 2006).…”