Genomics-assisted discovery of clubroot resistance gene Crr5 and its application in breeding of Chinese cabbage

Here, we presented a high-quality chromosome-level genome sequence of clubroot resistant line DH40, a doubled haploid line derived from the hybrid offspring of a Europe turnip ECD01 and two Chinese cabbage lines. The assembly was 420.92 Mb in length with a contig N50 of 11.97 Mb. The DH40 genome provided direct reference and greatly facilitate the map-based cloning of the clubroot resistance gene Crr5, encoding a nucleotide-binding leucine-rich repeat (NLR) protein. Further functional analysis showed that the Crr5 conferred clubroot resistance in Arabidopsis and Chinese cabbage, responded with the inoculation of Plasmodiophora brassicae, expressed both in roots and leaves, localized in nucleus, and the TIR domain alone could be autoactivated and elicited cell death. Most importantly, we developed two Crr5-specific KASP markers and successfully applied in breeding of clubroot resistant varieties through marker-assisted selection. Overall, our study provides valuable resource for genetic and genomic studies in B. rapa, and deepens our understanding of molecular mechanism underlying clubroot resistance against to Plasmodiophora brassicae.