The recent identification of the Crr5 gene in a clubroot-resistant Chinese cabbage line represents a significant advancement in combating the soil-borne pathogen Plasmodiophora brassicae, which poses a severe threat to cruciferous crop production worldwide. This groundbreaking research, conducted by scientists from the Henan Academy of Agricultural Sciences and Peking University, was published on March 1, 2025, in Horticulture Research.
Clubroot disease is notorious for its ability to persist in soil for up to 20 years, leading to yield losses that can exceed 40% during severe outbreaks. While more than 20 loci associated with clubroot resistance have been identified in Brassica rapa, only two genes—CRa and Crr1a—have previously been isolated and functionally validated. The frequent breakdown of resistance in cultivated varieties underscores the necessity for comprehensive genomic studies to discover new resistance genes and to create reliable molecular markers for sustainable management of clubroot.
The researchers successfully constructed a chromosome-level reference genome of the doubled haploid line DH40, which is pivotal in identifying the Crr5 gene. Using advanced techniques including next-generation sequencing and Hi-C technologies, the team localized Crr5 on chromosome A08 and demonstrated its functional significance in both Chinese cabbage and transgenic Arabidopsis thaliana. The DH40 genome, measuring 420.92 Mb with a contig N50 of 11.97 Mb, is one of the most comprehensive assemblies for this species to date.
Through comparative genomic analysis, DH40 was found to be more genetically similar to the Chinese cabbage cultivar “Chiifu” than to the turnip “ECD04”. The researchers employed bulked segregant analysis (BSA) alongside map-based cloning to swiftly identify the Crr5 locus on chromosome A08. This gene encodes a TIR-NBS-LRR protein located in the nucleus, characterized by a TIR domain that can self-activate and induce cell death—crucial elements of plant immune signaling.
Expression profiling indicated that Crr5 is responsive to inoculation with P. brassicae, showing peak expression levels seven days post-infection in resistant lines. Functional validation in transgenic Arabidopsis confirmed that the presence of Crr5 alone is sufficient to confer resistance against clubroot.
In a bid to facilitate breeding efforts, the researchers also developed two Kompetitive Allele-Specific PCR (KASP) markers specific to Crr5, which enable efficient marker-assisted selection. The successful development of a resistant near-isogenic line, R16-Crr5, through backcrossing demonstrated complete resistance to the P. brassicae isolate PbXY-2.
Dr. Xiaowei Zhang, the corresponding author of the study, emphasized, “Crr5 not only represents a novel resistance gene but also a key molecular tool for developing durable clubroot-resistant cultivars.” The researchers believe that their high-quality reference genome will facilitate precise gene discovery and comparative genomic studies in Brassica rapa. The identification of Crr5 paves the way for stacking multiple resistance loci and designing improved breeding strategies aimed at protecting cruciferous crops from long-lasting soil-borne pathogens.
The finding of the Crr5 gene is a significant leap forward in breeding efforts for clubroot-resistant Chinese cabbage and related Brassica crops. The availability of a high-quality genome sequence for DH40 not only streamlines gene mapping but also provides essential genomic resources for improving disease resistance. The new Crr5-specific molecular markers are set to enhance the efficiency of producing resistant varieties through marker-assisted selection, and the functional characterization of Crr5 enriches the understanding of plant immune signaling, aiding future endeavors in engineering multi-gene resistance systems to bolster global crop resilience against clubroot disease.
Funding for this study was provided by the National Natural Science Foundation of China, Zhongyuan Sci-Tech Innovation Leading Talents, the Key Sci-Tech R&D Project of Joint Foundation in Henan Province, and other distinguished scholarship programs.
About Horticulture Research: Horticulture Research is an open access journal published by Nanjing Agricultural University, recognized as the top journal in the Horticulture category according to the 2023 Journal Citation Reports from Clarivate. It aims to publish original research articles, reviews, and other contributions related to all major horticultural plants and disciplines.
