Integrated BSA-seq and RNA-seq analysis to identify candidate genes associated with nitrogen utilization efficiency (NUtE) in rapeseed (Brassica napus L.)

Rapeseed (Brassica napus L.) is one of the important oil crops, with a high demand for nitrogen (N). It is essential to explore the potential of rapeseed to improve nitrogen utilization efficiency (NUtE). Rapeseed is an allotetraploid crop with a relatively large and complex genome, and there are few studies on the mapping of genes related to NUtE regulation. In this study, we used the combination of bulk segregant analysis sequencing (BSA-Seq) and RNA sequencing (RNA-Seq) to analyze the N-efficient genotype 'Zheyou 18' and N-inefficient genotype 'Sollux', to identify the genetic regulatory mechanisms. Several candidate genes were screened, such as the high-affinity nitrate transporter gene NRT2.1 (BnaC08g43370D) and the abscisic acid (ABA) signal transduction-related genes (BnaC02g14540D, BnaA03g20760D, and BnaA05g01330D). BnaA05g01330D was annotated as ABA-INDUCIBLE bHLH-TYPE TRANSCRIPTION FACTOR (AIB/bHLH17), which was highly expressed in the root. The results showed that the primary root length of the ataib mutant was significantly longer than that of the wild type under low N conditions. Overexpression of BnaA5.AIB could reduce the NUtE under low N levels in Arabidopsis (Arabidopsis thaliana). Candidate genes identified in this study may be involved in the regulation of NUtE in rapeseed, and new functions of AIB in orchestrating N uptake and utilization have been revealed. It is indicated that BnaA5.AIB may be the key factor that links ABA to N signaling and a negative regulator of NUtE. It will provide a theoretical basis and application prospect for resource conservation, environmental protection, and sustainable agricultural development.