Disease relevance of NIR1

• Transgenic plants of Arabidopsis bearing the spinach (Spinacia oleracea) nitrite reductase (NiR, EC 1.7.7.1) gene that catalyzes the six-electron reduction of nitrite to ammonium in the second step of the nitrate assimilation pathway were produced by use of the cauliflower mosaic virus 35S promoter and nopaline synthase terminator [1].

High impact information on NIR1

• In addition to known nitrate-responsive genes (e.g. those encoding nitrate transporters, nitrate reductase, nitrite reductase, ferredoxin reductase, and enzymes in the pentose phosphate pathway), genes encoding novel metabolic and potential regulatory proteins were found [2].
• Each of the latter three had one to two copies of spinach NiR cDNA per haploid genome [1].
• When these plants were grown in vitro on media containing either nitrate or ammonium as sole nitrogen source, NiR mRNA derived from transgene expression was constitutively expressed, whereas NiR activity and protein level were strongly reduced on ammonium-containing medium [3].
• Addition of a nitric oxide synthase inhibitor to block nitric oxide generation by the plant prevented gfp expression in infiltrated nitrite reductase mutants, demonstrating that plant-derived nitric oxide can activate nor expression in infiltrated cells [4].
• The amount of UN derived from NO2 was greatly increased in the transgenic tobacco clone 271 (Vaucheret et al., 1992) where the activity of nitrite reductase is suppressed less than 5% of that of the wild-type plant [5].

Biological context of NIR1

• Nucleotide sequence of a gene for nitrite reductase from Arabidopsis thaliana [6].
• Based on the comparison with the spinach cDNA, the Arabidopsis NiR gene was concluded to contain 4 exons [exon 1 of 376 bp (beginning with ATG start codon), exon 2 of 355 bp, exon 3 of 289 bp and exon 4 of 741 bp (ending at TGA stop codon)] and 3 introns (intron 1 of 196 bp, intron 2 of 81 bp and intron 3 of 77 bp) [6].
• The deduced amino acid sequence of the coding region of the Arabidopsis NiR gene had high similarities with those of NiR genes of other plants including spinach [6].
• A nitrite reductase (NiR) gene was recovered from Arabidopsis thaliana genomic library by the homology with a cDNA of spinach NiR and sequenced [6].

Associations of NIR1 with chemical compounds

• Higher plant nitrite reductase (NiR) is a monomeric chloroplastic protein catalysing the reduction of nitrite, the product of nitrate reduction, to ammonium [3].

References