Optimization of carbon and nitrogen utilization for enhanced photosynthesis, biomass and yield by coexpression of phosphoenolpyruvate carboxylase, aspartate aminotransferase and glutamine synthetase in Brassica juncea

Summary Coexpression of genes involved in carbon (C) and nitrogen (N) metabolism offers a promising avenue for improving crop yield. This study investigated the impact of coexpressing phosphoenolpyruvate carboxylase [ ZmPEPC ( P )], aspartate aminotransferase [ GmAspAT ( A )] and glutamine synthetase [ NtGS ( G )] in Brassica juncea to enhance plant yield through improved C and N utilization. Plants coexpressing three genes ( BjPAG ) showed a significant increase in plant growth, biomass, chlorophyll and carotenoid content, while exhibiting decreased anthocyanin and hydrogen peroxide production. These improvements were observed under both ambient (~400 ppm; ACO 2 ) and low (~200 ppm; LCO 2 ) atmospheric CO 2 conditions. Chlorophyll fluorescence study revealed that BjPAG plants had higher photosynthetic efficiency, particularly increased maximum quantum yield of PSII and performance index. This facilitated increased CO 2 assimilation, total soluble sugar and starch accumulation, along with altered stomatal traits under both ACO 2 and LCO 2 conditions. Additionally, BjPAG plants accumulated less ammonium than control plants under both CO 2 levels, indicating effective functioning of the overexpressed genes. Improved performance (enhanced photosynthetic rates, biomass and seed yield) of BjPAG plants under various N environments (6, 3 and 0.3 m m N) also supported improved N utilization. NMR analysis suggested that PAG ‐coexpression resulted in a higher flux of assimilated CO 2 and NH 3 towards sugars, amino acids, organic acids, polyphenols and glucosinolates. In conclusion, this study highlights the effectiveness of coexpressing ZmPEPC , GmAspAT and NtGS in B. juncea , leading to efficient C and N utilization, ultimately resulting in enhanced photosynthesis, plant biomass and seed yields, and as a promising strategy for increasing the yield of food crops.