Root-associated microbiota involved the protein quality formation of grains under nitrogen application in wheat: Implications for sustainable production and industrial applications

Wheat grain protein possess multifunctional properties that make them valuable for industrial applications. Nitrogen is an important factor affecting the accumulation of protein in wheat grains. Root-associated microbiota plays a critical role in plant nutrition and productivity, which is susceptible to the influence of environmental factor nitrogen. However, how microbial communities assemble in wheat rhizosphere under elevated nitrogen input to affect grain protein quality is not well understood. This study investigated the effects of nitrogen application on bacterial communities, agronomic traits, nitrogen accumulation, and grain protein quality in wheat. Nitrogen application significantly decreased richness, diversity, and evenness of the rhizospheric bacterial community, whereas it increased richness of root endophytes. 34 and 10 differential bacterial taxa were identified in the rhizosphere soil and root endosphere under nitrogen treatment, respectively. The genera Bosea, Alysiosphaera, Sphingopyxis, Devosia, Nitrosospira, and Taibaiella were markedly enriched in the rhizosphere under nitrogen treatment. Nitrogen-induced shifts in root-associated bacterial communities subsequently caused changes in wheat growth traits, with enhanced nitrogen remobilization from stems to grains under nitrogen application. Meanwhile, the grain total protein content with 26.30 % of enhancement at N150 level and 49.29 % of enhancement at N300 level was primarily reflected in the increase of gliadin and glutenin accumulation. Mantel test results showed that nitrogen-enriched bacterial taxa, mainly within the phyla Proteobacteria and Bacteroidota, were significantly correlated with grain protein content with correlation coefficient of 0.77 in the rhizosphere soil and 0.71 in the root endosphere respectively. In conclusion, nitrogen-driven enrichment of bacterial taxa in wheat rhizosphere could improve grain protein quality by promoting root growth and enhancing nitrogen utilization and remobilization. The results provided new insights into the role of root-associated microbiota in grain quality formation under nitrogen regulation, which is of great importance for wheat sustainable production and the industrial application of wheat protein.