Molecular physiology of plant nitrogen use efficiency and biotechnological options for its enhancement

Nitrogen use efficiency (NUE) in plants is a complex phenomenon that depends on a number of internal and external factors, which include soil nitrogen availability, its uptake and assimilation, photosynthetic carbon and reductant supply, carbon-nitrogen flux, nitrate signalling and regulation by light and hormones, to name a few. The molecular basis for organism-wide regulation of nitrate assimilation is not yet fully understood, and biotechnological interventions to improve crop NUE have met with limited success so far. This article summarizes the physiological, biochemical and molecular aspects of NUE, QTL mapping studies as well as transgenic efforts to improve it in crop plants and model plants. It encompasses primary and secondary N-assimilatory pathways and their interplay with carbon metabolism, as well as signalling and regulatory components outside the metabolic cascade. The article highlights the need for an integrated approach combining fertilizer management techniques with biotechnological interventions to improve N flux and NUE for Indian crop cultivars.