Comparative Proteomic Analysis of Two Contrasting Maize Hybrids' Responses to Low Nitrogen Stress at the Twelve Leaf Stage and Function Verification of

Nitrogen is one of the essential nutrients for plant growth and development. However, large amounts of nitrogen fertilizer not only increase the production costs, but also lead to serious environmental problems. Therefore, it is particularly important to reduce the application of nitrogen fertilizer and develop maize varieties with low nitrogen tolerance. The aim of this study was to determine the phenotypic and proteomic alterations of maize affected by nitrogen deficiency and to elucidate the molecular and physiological mechanisms underpinning maize tolerance to low nitrogen. Two maize hybrids with contrasting low nitrogen tolerance were used as the experimental materials. Maize plants were grown under different nitrogen application levels (N0 and N240) and proteomic analysis performed to analyze leaf differentially abundant proteins (DAPs) under different nitrogen conditions. The results showed that under the nitrogen deficiency condition, the nitrogen content, leaf dry weight, leaf area, and leaf area index of XY335 decreased by 15.58%, 8.83%, 3.44%, and 3.44%, respectively. However, in the variety HN138, the same parameters decreased by 56.94%, 11.97%, 8.79%, and 8.79%, respectively. Through proteomic analysis, we found that the low nitrogen tolerance variety responded to low nitrogen stress through lignin biosynthesis, ubiquitin-mediated proteolysis, and stress defense proteins. Transmembrane transporters were differentially expressed in both hybrids after low nitrogen treatment, suggesting that this was a common response to low nitrogen stress. Using bioinformatics analysis, we selected the key candidate gene (