The Responses of Genotypes with Contrasting NUtE to Exogenous ABA During the Flowering Stage in Brassica Napus

A large amount of nitrogen (N) fertilizer is applied to maintain a stable yield because of the low N utilization efficiency (NUtE) in rapeseed (Brassica napus L.), which increases production costs and has a negative impact on the environment. Abscisic acid (ABA) has been reported to have crosstalk with nitrate. In this study, exogenous ABA treatment and RNA-seq were used to explore the response patterns of rapeseed with contrasting NUtE to ABA signals. Our 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. Transcriptome analysis showed the DEGs were mainly enriched in N metabolism, ABC transporters, and MAPK signaling pathways. Among them, the Glutamate dehydrogenase (GS) genes and the Glutamine synthetase gene were more highly expressed in the N-efficient genotype leaf than the N-inefficient genotype after ABA treatment. In contrast, the opposite expression level was observed in seven genes, including nitrate transporter 2.1, Nitrate Reductase genes, and GS genes in the root. In 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, which may be one of the reasons for the difference in NUtE