The responses of genotypes with contrasting NUtE to exogenous ABA during the flowering stage in Brassica napus

[Objective]Abscisic acid(ABA)has been reported to have crosstalk with nitrate().The aim of this study was to explore the responses of genotypes with contrasting nitrogen utilization efficiency(NUtE)to exogenous ABA during the flowering stage in Brassica napus,and to identify candidate genes that may be involved in the regulation of NUtE.[Method]In the pot experiment,"Zheyou 18"and"Sollux"were grown in a greenhouse.On the tenth day after flowering,bottom leaves were sprayed with 2 μM ABA.For the hydroponic experiment,plants were treated with 50 μM ABA on the tenth day after flowering.The leaves and roots were sampled after a six-hour treatment for transcriptome analysis.[Result]The results showed that ABA application on leaf promoted the N allocation from vegetative organs to grain and increased the number of seeds per silique,grain yield,N harvest index(NHI),and the NUtE in N-efficient rapeseed,while that in the N-inefficient genotype showed a declined trend.After hydroponic ABA treatment,transcriptome analysis showed that there were more differentially expressed genes(DEGs)in the N-efficient genotype than that in the N-inefficient genotype.The DEGs were mainly enriched in N metabolism,ABC transporters,and MAPK signaling pathways.Among them,Glutamate dehydrogenase(GDH)genes(BnaC09g47860D,BnaC03g03050D)and Glutamine synthetase(GS)gene(BnaC03g40250D)was more highly expressed in the leaf of N-efficient genotype than that of N-inefficient genotype after ABA treatment,whereas the opposite expression level was observed in seven genes,including nitrate transporter(NRT)2.1(BnaA06g04570D),Nitrate Reductase(NR)genes(BnaC06g20690D,BnaA07g20840D),GSs(BnaC04g29670D,BnaC08g07930D,BnaA08g29950D,BnaA04g07450D),and Abscisic acid-responsive element binding factor(ABFs)genes(BnaC07g44670D,BnaC05g33570D)in the root.[Conclusion]the shoot and root of rapeseed may have different response mechanisms to ABA stimulation,and N-efficient rapeseed is more sensitive to ABA treatment than N-inefficient rapeseed,which may be one of the reasons for the difference in NUtE.The study revealed the critical role of ABA in regulating N allocation and utilization in rapeseed with contrasting NUtE and identified several candidate genes involved in the crosstalk between ABA and signaling,which provided target genes for breeding N-efficient rapeseed.