Background: Plants have evolved disease resistance (R) genes encoding for nucleotide-binding site (NB) and leucine-rich repeat (LRR) proteins with N-terminals represented by either Toll/Interleukin-1 receptor (TIR) or coiled-coil (CC) domains. Here, a genome-wide study of presence and diversification of CC-NB-LRR and TIR-NB-LRR encoding genes, and shorter domain combinations in 19 Arabidopsis thaliana accessions and Arabidopsis lyrata, Capsella rubella, Brassica rapa and Eutrema salsugineum are presented.
Results: Out of 528 R genes analyzed, 12 CC-NB-LRR and 17 TIR-NB-LRR genes were conserved among the 19 A. thaliana genotypes, while only two CC-NB-LRRs, including ZAR1, and three TIR-NB-LRRs were conserved when comparing the five species. The RESISTANCE TO LEPTOSPHAERIA MACULANS 1 (RLM1) locus confers resistance to the Brassica pathogen L. maculans the causal agent of blackleg disease and has undergone conservation and diversification events particularly in B. rapa. On the contrary, the RLM3 locus important in the immune response towards Botrytis cinerea and Alternaria spp. has recently evolved in the Arabidopsis genus.
Conclusion: Our genome-wide analysis of the R gene repertoire revealed a large sequence variation in the 23 cruciferous genomes. The data provides further insights into evolutionary processes impacting this important gene family.