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

[Objective]Heterotrimeric G-proteins,composed of Gα,Gβ,and Gγ subunits,are involved in the regulation of a variety of 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.[Method]overexpressing transgenic lines AtAGB1 and AtAGG1(AtGβγ1),AtAGB1 and AtAGG2(AtGβγ2),and AtAGB1 and AtAGG3(AtGβγ3)were created in K407 Brassica napus(B.napus)backgrounds concurrent as well as AtGPA1(AtGα1)overexpressing lines.The yield,nitrogen utilization efficiency(NUE),and related parameters of overexpressed Arabidopsis G-protein were determined.[Result]Analysis of multiple transgenic B.napus lines showed that overexpression of AtGα1,AtGβγ1,AtGβγ2 and AtGβγ3 could increase the biomass of seedling plants with a well-developed root system and increased nitrogen uptake under both nitrogen conditions.Under low nitrogen,the activity of glutamine synthetase(GS),a key nitrogen assimilating enzymes,and the expression levels of genes involved in nitrogen uptake and assimilation exhibited a significant increase in root of overexpressed plants.More importantly,these properties enabled overexpressing plants to increase the number of seeds per silique only under low nitrogen condition,effectively resulting in a significant increase in yield per plant and better NUE.Especially,overexpression of AtGβγ3 increased seed yield by 31%-69%and NUE by 27%-42%compared with wild-type(WT).[Conclusion]These results draw the positive roles of G-protreins in regulating two key parameters,seed traits and nitrogen use efficiency,and provide a strategy that can substantially improve crop yield and nitrogen use efficiency.