Nitrite reductase gene expression

Back, E., Dunne, W., Schneiderbauer, A., de Framond, A., Rastogi, R. Rothstein, S.J. (1991). Isolation of the spinach nitrite reductase gene promoter which confers nitrate inducibility on GUS gene expression in transgenic tobacco. Plant Molecular Biology 17, 9-18. 

In various species of bacteria several different types of non-assimilatory nitrite reductases are found. Escherichia coli has a cytoplasmic NAD(P)H-dependent enzyme whose role seems to be detoxification of nitrite. This type of enzyme, coded for by the nirB gene, also contains siroheme as the redox active catalytic center (Cole, 1988). Additionally in E. coli, and expressed under different conditions to the cytoplasmic enzyme, is a periplasmic nitrite reductase that catalyses formation of ammonia from nitrite (Cole, 1988). This enzyme has five c-type (Figure 1) hemes per polypeptide chain one of these hemes, the catalytic site, has the unique CXXCK sequence as its attachment site (Einsle et al., 1999). Electrons reach this type of nitrite reductase, which is fairly widely distributed amongst the microbial world, from the cytoplasmic membrane electron transfer chain. The exact electron donor partner from such chains for this type of nitrite reductase is unknown (Berks et al., 1995). 

Kramer etfl/., 1989 Wvalle eta/., 1989). Nitrite reductase mRNA was present in small amounts in uninduced leaves of both species but not in roots of maize. Induction by nitrate increased the NiR mRNA in both species and in both the roots and leaves of maize. Perhaps one of the two NiR genes present in maize is expressed constitutively in leaves (Kramer et al., 1989). The NiR mRNA induction pattern in maize (Kramer et al., 1989) is similar to the NR mRNA induction pattern in barley (Melzer et al., 1989). Nitrite reductase mRNA is rapidly induced by nitrate, reaching a peak within 5 hr and then declining to a lower level even in the presence of continued nitrate. The NiR mRNA appears to be short lived with a half-life as short as 30 min (Kramer et al, 1989). The mechanisms regulating these fluctuations in NiR mRNA are not known at this time. Nitrite was capable of limited induction of NiR mRNA in spinach leaves (Back etal, 1988), although the role of nitrite is equivocal due to Ae possibility of in vivo oxidation of nitrite to nitrate (Aslam et al, 1987). 

Nitrate assimilation is an important process in rice regeneration. A quantitative trait loci gene encoding the ferrodoxin-nitiite reductase (NiR), an enzyme that catalyzes the reduction of nitrite to ammonium leading to the accumulation of toxic nitrite in culture media, was isolated from the high-regeneration rice strain Kasalath. The level of NiR expression in the... 

---