Transcription factors involved in controlling the expression of nitrate reductase genes in higher plants

Nitrate reductase is a key enzyme in nitrogen assimilation, and it catalyzes the nitrate-to-nitrite reduction process in plants. A variety of factors, including nitrate, light, metabolites, phytohormones, low temperature, and drought, modulate the expression levels of nitrate reductase genes as well as nitrate reductase activity, which is consistent with its physiological role. Recently, several transcription factors involved in controlling the expression of nitrate reductase genes have been identified in Arabidopsis. NODULE-INCEPTION-like proteins (NLPs) are transcription factors responsible for nitrate-inducible expression of nitrate reductase genes. Since NLPs also control nitrate-inducible expression of genes encoding nitrate transporter, nitrite transporter, and nitrite reductase, the expression levels of nitrate reduction pathway-associated genes are coordinately modulated by NLPs in response to nitrate. LATERAL ORGAN BOUNDARIES DOMAIN (LBD) transcription factors (LBD37-LBD39) are strong candidates for transcription factors mediating negative feedback regulation in response to increases in the contents of nitrogen-containing metabolites, whereas LONG HYPOCOTYL 5 (HY5) that promotes photomorphogenesis in light may be a transcription factor involved in light-induced expression of a nitrate reductase gene. Furthermore, unidentified transcription factors likely mediate other signals and regulate the expression of nitrate reductase genes. This review presents a summary of our current knowledge of such transcription factors.