Genomics of Nitrogen Use Efficiency in Maize: From Basic Approaches to Agronomic Applications

Maize farming requires high amounts of nitrogen (N) fertilizer, which can have detrimental effects on agronomic sustainability and the environment. Thus, irrespective of the mode of N fertilization, an increased knowledge of the mechanisms controlling plant N metabolism is essential for improving nitrogen use efficiency (NUE) in maize. This new knowledge will reduce the excessive input of fertilizers, while maintaining an acceptable yield and a sufficient profit margin for the farmers. It is now possible to further develop whole-plant agronomic and physiological studies. These can be combined with gene, protein, and metabolite profiling to build up a comprehensive picture depicting the different steps of N uptake, assimilation, and recycling to produce either biomass in vegetative organs or proteins in storage organs. We provide an overview describing how our understanding of the physiological and molecular controls of N assimilation in maize has been advanced using combined approaches. These are based on agronomic, whole-plant physiology, genetic, modeling, and systems biology approaches. Current knowledge and prospects for selecting high-yielding maize genotypes adapted to lower N fertilizer input and for identifying biological markers representative of the plant N status for breeding and agronomic purposes are reviewed.