Enhancing seed yield and nitrogen use efficiency of Brassica napus L. under low nitrogen by overexpression of G-proteins from Arabidopsis thaliana.

Heterotrimeric G-proteins, composed of Gα, Gβ, and Gγ subunits, are involved in the regulation of multiple signaling pathways in plants. OsDEP1 (Gγ subunit-encoded protein) of rice and TaNBP1 (Gβ subunit-encoded protein) of wheat are homologs of Arabidopsis AGG3 and AGB1, respectively, which are regulators of grain size and also involved in nitrogen responses. However, the function of Arabidopsis G-proteins in nitrogen utilization under different nitrogen conditions has not been fully investigated. In this study, to evaluate the role of Arabidopsis G-proteins towards yield and nitrogen use efficiency (NUE), overexpressing transgenic lines AtGPA1, AtAGB1 together with AtAGG1 (AGB1-AGG1), with AtAGG2 (AGB1-AGG2), and with AtAGG3 (AGB1-AGG3) were created in the "K407" Brassica napus (B. napus). Analysis of multiple transgenic B. napus lines showed that overexpression of GPA1, AGB1-AGG1, AGB1-AGG2, or AGB1-AGG3 increased the biomass of seedling plants including a well-developed root system and increased nitrogen uptake under low and high nitrogen conditions. The activity of glutamine synthetase (GS), a key nitrogen assimilating enzyme, as well as the expression levels of genes that are involved in nitrogen uptake and assimilation were significantly increased in overexpressing plants under low nitrogen conditions. These properties enabled overexpressing plants to increase the number of seeds per silique by 12%-27% only under low nitrogen condition, effectively improving yield per plant by 9%-69% and NUE by 7%-49%. These results reveal roles of G-proteins in regulating seed traits and NUE, and provide a strategy that can substantially improve crop yield and NUE.