NLP Transcription Factors Governing Nitrate-Responsive Gene Expression

Nitrate is the most abundant inorganic form of nitrogen in soils and a major source of nitrogen for plants. As a signaling molecule in plants, nitrate also plays critical roles in regulating a variety of physiological processes, including expression of nitrogen assimilation-related genes. We previously identified a nitrate-responsive cis-element (NRE) that is conserved among promoters of nitrite reductase gene from many plant species (1,2). Recently, we found that NIN-like proteins (NLPs) bind to the NRE and function as transcriptional activators that mediate nitrate signal (3,4). NLPs directly regulated expression of genes encoding nitrogen assimilation-related proteins, including nitrate transporter, nitrate reductase, chroloplastic nitrite transporter and nitrite reductase, in Arabidopsis (3,5-9). Furthermore, by transcriptome analysis with transgenic Arabidopsis plants in which NLP activity was reduced, NLPs were found to control expression of most of nitrate-responsive genes directly or indirectly. Hence, NLPs were identified as master regulators for nitrate response (8). These may implicate that enhancing NLP activity leads to improvement of nitrogen utilization efficiencies (NUE) of plants. However, since NLP activity is post-translationally regulated by nitrate signal (4), contrivances are necessary for development of a new strategy for improvement of NUE with NLPs. I will discuss our future challenge to improve NUE with NLPs. (1) Plant J. 63:269, 2010. (2) BBRC, 411:708, 2011. (3) Nat. Commun. 4:1617, 2013. (4) Plant Signal Behav. 8: e25975, 2013. (5) PCP 52:824, 2011. (6) SSPN 59:612, 2013. (7) PCP 55:1311, 2014. (8) JXB, 65:5589, 2014. (9) Plant Sci. 229:167, 2014.