Identification and expression profiling analysis of NBS–LRR genes involved in Fusarium oxysporum f.sp. conglutinans resistance in cabbage

Abstract

As one of the most important resistance (R) gene families in plants, the NBS–LRR genes, encoding proteins with nucleotide-binding site (NBS) and leucine-rich repeat (LRR) domains, play significant roles in resisting pathogens. The published genomic data for cabbage (Brassica oleracea L.) provide valuable data to identify and characterize the genomic organization of cabbage NBS–LRR genes. Ultimately, we identified 105 TIR (N-terminal Toll/interleukin-1 receptor)-NBS–LRR (TNL) genes and 33 CC (coiled-coil)-NBS–LRR (CNL) genes. Further research indicated that 50.7% of the 138 NBS–LRR genes exist in 27 clusters and there are large differences among the gene structures and protein characteristics. Conserved motif and phylogenetic analysis showed that the structures of TNLs and CNLs were similar, with some differences. These NBS–LRRs are evolved under negative selection and mostly arose from whole-genome duplication events during evolution. Tissue-expression profiling of NBS–LRR genes revealed that 37.1% of the TNL genes are highly or specifically expressed in roots, especially the genes on chromosome 7 (76.5%). Digital gene expression and reverse transcription PCR analyses revealed the expression patterns of the NBS–LRR genes upon challenge by Fusarium oxysporum f.sp. conglutinans: nine genes were upregulated, and five were downregulated. The major resistance gene Foc1 probably works together with the other four genes in the same cluster to resist F. oxysporum infection.