Integrated genomic and transcriptomic insights into the two-component high-affinity nitrate transporters in allotetraploid rapeseed

Abstract

The two-component high-affinity nitrate (NO3-) transport system (THATS) proteins (NRT2/NAR2) play key roles in the efficient nitrogen (N) uptake and transport under N limitations. We aimed at uncovering the core THATS gene(s) regulating N use efficiency (NUE) in allotetraploid rapeseed (Brassica napus L.). Genomic information, high-throughput transcriptome sequencing and gene co-expression network were integrated to identify and characterize the core THATS genes. We identified 17 BnaNRT2 and eight BnaNAR2.1 homologs spanning across the rapeseed genome. Copy number and gene presence/absence variations of BnaNRT2s/BnaNAR2.1 s, undergoing strong purifying selection, occurred. The over-representation of Dof, MYB and WRKY cis-regulatory elements and the enrichment of CpG islands, and protein phosphorylation sites indicated the importance of transcriptional and epigenetic regulation in the BnaNRT2 activities, respectively. qRT-PCR assays and high-throughput RNA-seq revealed that both BnaNRT2s and BnaNAR2.1 s were expressed preferentially in the roots; and they showed significantly differential expression under different N forms or different levels of NO3- supply. A gene co-expression network identified BnaC8.NRT2.1a and BnaC2.NAR2.1 as the core THATS genes. The core THATS members can serve as elite gene resources for crop NUE improvement. The transcriptomics-assisted gene co-expression network analysis provides novel insights regarding the rapid identification of central members within large gene families of plant species with complex genomes.