Researchers Discover Novel Clubroot Resistance Gene Crr5 in Chinese Cabbage

Clubroot disease, caused by Plasmodiophora brassicae, is a devastating soil-borne pathogen that severely threatens global production of cruciferous crops. It can persist in soil for up to two decades, causing yield losses exceeding 40% in severe outbreaks. Although over 20 clubroot-resistant loci have been reported in Brassica rapa, only two genes-CRa and Crr1a-had been successfully isolated and functionally validated. Moreover, resistance breakdown has frequently occurred in cultivated varieties. Due to these challenges, it is necessary to conduct in-depth genomic and functional research to identify novel resistance genes and develop reliable molecular markers for sustainable clubroot control.

Researchers from the Henan Academy of Agricultural Sciences and Peking University have constructed a chromosome-level reference genome of the doubled haploid line DH40 and identified the clubroot resistance gene Crr5. The study (DOI: 10.1093/hr/uhae338), published on March 1, 2025, in Horticulture Research, provides a new molecular framework for combating P. brassicae infection in Chinese cabbage. By integrating next-generation sequencing, PacBio HiFi, and Hi-C technologies, the team pinpointed Crr5 on chromosome A08 and demonstrated its functional role in both Chinese cabbage and transgenic Arabidopsis thaliana.

The DH40 genome, spanning 420.92 Mb with a contig N50 of 11.97 Mb, represents one of the most complete assemblies for B. rapa. Comparative genomic analysis revealed that DH40 is genetically closer to the Chinese cabbage cultivar 'Chiifu' than to the turnip 'ECD04'. Bulked segregant analysis (BSA) combined with map-based cloning rapidly located the Crr5 locus on chromosome A08. The gene encodes a TIR-NBS-LRR protein localized in the nucleus, with its TIR domain capable of self-activation and cell death induction-key features of plant immune signaling. Expression profiling showed that Crr5 responds to P. brassicae inoculation, with peak expression at 7 days post-infection in resistant lines. Functional validation through transgenic Arabidopsis confirmed that Crr5 alone is sufficient to confer clubroot resistance. To accelerate breeding applications, researchers developed two Crr5-specific Kompetitive Allele-Specific PCR (KASP) markers, enabling efficient marker-assisted selection. Using these markers, a resistant near-isogenic line, R16-Crr5, was successfully developed through backcrossing, showing complete resistance to P. brassicae isolate PbXY-2.

Crr5 not only represents a novel resistance gene but also a key molecular tool for developing durable clubroot-resistant cultivars. By providing a high-quality reference genome, our study enables precise gene discovery and comparative genomic analysis in Brassica rapa. The identification of Crr5 opens new possibilities for stacking multiple resistance loci and designing improved breeding strategies to protect cruciferous crops from one of the most persistent soil-borne pathogens."

Dr. Xiaowei Zhang, corresponding author 

The discovery of Crr5 offers a crucial advancement for breeding clubroot-resistant Chinese cabbage and related Brassica crops. The availability of a high-quality genome sequence for DH40 facilitates rapid gene mapping and provides valuable genomic resources for resistance improvement. The newly developed Crr5-specific molecular markers can be directly applied in marker-assisted selection to produce resistant varieties efficiently. Beyond practical breeding, the functional characterization of Crr5 deepens understanding of plant immune signaling, contributing to future efforts in engineering multi-gene resistance systems and enhancing global crop resilience against clubroot disease.