It is a global challenge to enhance yield while still maintaining grain-quality attributes such as grain protein content in wheat breeding programme due to the negative correlation between grain yield and grain protein content. Protein abundance in wheat grain is determined by the relative rates of protein synthesis and protein degradation occurring during grain development.

The stability of any given protein during grain development defines its N sink strength in the formation of mature grain. Through combining in vivo 15N stable isotope labelling and in-depth quantitative proteomics, we have measured the turnover rates and N sink strength of 1400 different types of proteins during wheat grain development.

Our data show that approximately 20% of total grain ATP production is used for grain protein biogenesis and maintenance, and nearly half of this energy budget is invested exclusively in storage protein synthesis. We demonstrate that wheat storage proteins are not as stable as we traditionally thought, and about 25% of newly synthesized storage proteins are turned over during grain development rather than stored, causing a 20% loss of N sink on a grain basis and a 6.6% loss of NUE on applied nitrogen basis.

Our approach to measure protein turnover rates at proteome scale reveals how different functional categories of grain proteins accumulate, calculates the ATP cost and N sink strength of each protein as it accumulates during wheat grain development and identifies the most and the least stable proteins in the developing wheat grain.

This can provide a new perspective on targets in quality wheat breeding through improving N sink strength and NUE by stabilizing storage proteins that turnover rapidly. Success in this pursuit could also help negate the inverse relationship between grain yield and grain protein content by making grain protein accumulation cheaper in terms of cellular energy costs.