Synthetic <i>Raphanobrassica</i> Genome Reveals Functional and Evolutionary Insights Into Clubroot Resistance Genes on Chromosome <scp>R5</scp>

Clubroot, a severe soil-borne disease caused by Plasmodiophora brassicae, poses a severe threat to global production of Brassicaceae oilseed crops and vegetables. To date, there has been a serious lack of clubroot-resistant germplasms in Brassica napus (AACC), necessitating the urgent development of novel disease-resistant germplasm. We present a high-quality genome assembly of an artificially synthesised allotetraploid Raphanobrassica (RRCC), which exhibits broad-spectrum immunity to diverse P. brassicae pathotypes. Using a sesquidiploid RACC as a genetic bridge, we developed B. napus-R. sativus (AACC-R) monosomic addition lines and mapped a major clubroot resistance (CR) locus on chromosome R5. Comparative genomic analysis identified 30 candidate CR genes in this region. Notably, overexpression of CRR5.5.11, which encodes a receptor-like protein, via hairy root transformation conferred significant resistance in susceptible B. napus. Evolutionary and functional analyses revealed conserved homologues of CRR5.5.11 in diploid Isatis tinctoria and triploid turnip ECD04. Furthermore, the ECD04 allele CRA3.2.2 also conferred clubroot resistance, indicating that CRR5.5.11 and CRA3.2.2 have originated from the same diploid ancestor. Our study elucidates the genetic and evolutionary basis of clubroot resistance in Raphanobrassica, providing novel germplasm, gene resources and theoretical insights for clubroot-resistance breeding in rapeseed and other Brassicaceae crops.