Breeding for Higher Yields of Wheat and Rice through Modifying Nitrogen Metabolism

Wheat and rice produce nutritious grains that provide 32% of the protein in the human diet globally. Here, we examine how genetic modifications to improve assimilation of the inorganic nitrogen forms ammonium and nitrate into protein influence grain yield of these crops. Successful breeding for modified nitrogen metabolism has focused on genes that coordinate nitrogen and carbon metabolism, including those that regulate tillering, heading date, and ammonium assimilation. Gaps in our current understanding include (1) species differences among candidate genes in nitrogen metabolism pathways, (2) the extent to which relative abundance of these nitrogen forms across natural soil environments shape crop responses, and (3) natural variation and genetic architecture of nitrogen-mediated yield improvement. Despite extensive research on the genetics of nitrogen metabolism since the rise of synthetic fertilizers, only a few projects targeting nitrogen pathways have resulted in development of cultivars with higher yields. To continue improving grain yield and quality, breeding strategies need to focus concurrently on both carbon and nitrogen assimilation and consider manipulating genes with smaller effects or that underlie regulatory networks as well as genes directly associated with nitrogen metabolism.

Automated summary

Wheat and rice are nutritious grains that contribute 32% of the protein in the human diet worldwide. Genetic modifications to enhance the assimilation of inorganic nitrogen forms into protein have been explored to improve the grain yield of these crops. However, there are still gaps in our understanding of nitrogen metabolism genes, species differences, the impact of soil environments, and the genetic architecture of nitrogen-mediated yield improvement. To continue increasing grain yield and quality, breeding strategies should focus on both carbon and nitrogen assimilation and consider manipulating genes with smaller effects or that are part of regulatory networks.