Identification and mapping of a novel dominant resistance gene, TuRB07 to Turnip mosaic virus in Brassica rapa.

KEY MESSAGE: A novel dominant resistance gene, TuRB07, was found to confer resistance to an isolate of TuMV strain C4 in B. rapa line VC1 and mapped on the top of chromosome A06. The inheritance of resistance to Turnip mosaic virus in Brassica rapa was investigated by crossing the resistant line, VC1 with the susceptible line, SR5, and genotyping and phenotyping diverse progenies derived from this cross. Both a doubled haploid population, VCS3M-DH, an F2 and two BC1 (F1 × VC1 and F1 × SR5) populations were created. Population tests revealed that the resistance to the TuMV C4 isolate in B. rapa is controlled by a single dominant gene. This resistance gene, TuRB07 was positioned on the top of linkage group A06 of the B. rapa genome through bulk segregation analysis and fine mapping recombinants in three doubled haploid- and one backcross population using microsatellite markers developed from BAC end sequences. Within the region between the two closely linked markers flanking TuRB07, H132A24-s1, and KS10960, in the Chiifu reference genome, two genes encoding nucleotide-binding site and leucine-rich repeat proteins with a coiled-coil motif (CC-NBS-LRR), Bra018862 and Bra018863 were identified as candidate resistance genes. The gene Bra018862 is truncated, but the gene Bra018863 has all the domains to function. Furthermore, the analysis of structural variation using resequencing data of VC1 and SR5 revealed that Bra018863 might be a functional gene because the gene has no structural variation in the resistant line VC1 when compared with Chiifu, whereas at the other NBS-LRR genes large deletions were identified in the resistant line. Allelic differences of Bra018863 were found between VC1 and SR5, supporting the notion that this gene is a putative candidate gene for the virus resistance.