Recent Advancements in Nitrogen Use Efficiency in Crop Plants Achieved by Genomics and Targeted Genetic Engineering Approaches

Nitrogen plays a crucial role in plant metabolism, growth, and development of plants, and its deficiency leads to severe growth retardation and reduced grain yield. The efficient utilization of nitrogenous fertilizers is needed to enhance crop yield and also to fetch the food demand of the world population. The accumulated nitrogen in the ecosystem leads to severe environmental pollution and health hazards to inhabited animals. However, nitrogen inside plants is regulated by a set of nitrogen metabolism genes, promoters, and transcription factors. Further, the identification and characterization of nitrogen metabolism genes in crop plants is a prerequisite for developing tailored crop plants for increased nitrogen use efficiency (NUE), grain yield, biomass, and other economic traits. Moreover, NUE is a complex trait, and breeding crops for improving NUE is still in the infancy stage. Therefore, a targeted and holistic approach is required for enhanced nitrogen uptake and its utilization. The precise modulation of key genes of nitrogen metabolism, amino acid biosynthesis, and carbon metabolism could result in enhancement of NUE, and the engineered crop plants for NUE traits were reported to be superior in terms of NUE and also incurred higher grain yield, biomass, and improved agronomical parameters as that of cultivated crop cultivars. In this review, we described the basics of nitrogen metabolism, genomics, and recently targeted genetic engineering strategies employed in crop plants for improving NUE.