Transport inhibitor response 1/auxin signaling f-box proteins (TIR1/AFBs) play important roles in the process of plant growth and development as auxin receptors. To date, no information has been available about the characteristics of the TIR1/AFB gene family in Brassica juncea var. tumida. In this study, 18 TIR1/AFB genes were identified and could be clustered into six groups. The genes are located in 11 of 18 chromosomes in the genome of B. juncea var. tumida, and similar gene structures are found for each of those genes. Several cis-elements related to plant response to phytohormones, biotic stresses, and abiotic stresses are found in the promoter of BjuTIR1/AFB genes. The results of qPCR analysis show that most genes have differential patterns of expression among six tissues, with the expression levels of some of the genes repressed by salt stress treatment. Some of the genes are also responsive to pathogen Plasmodiophora brassicae treatment. This study provides valuable information for further studies as to the role of BjuTIR1/AFB genes in the regulation of plant growth, development, and response to abiotic stress.

Disease caused by Plasmodiophora brassicae severely disrupts cruciferous crops by altering root physiology and rhizosphere ecology. While pathogen-induced shifts in rhizosphere microbiomes are documented, the mechanisms linking root exudate reprogramming to microbial community remodeling remain poorly understood. Here, we integrated untargeted metabolomics and 16S rRNA sequencing to investigate how root exudates reshape the rhizosphere microbiome of tumorous stem mustard (Brassica juncea var. tumida) through P. brassicae infection. Metabolomic profiling identified 1718 root exudate metabolites, with flavones (e.g., apigenin 7-O-β-D-rutinoside, VIP > 1.5) and phenolic derivatives (e.g., gastrodin) being selectively enriched in infected plants. P. brassicae infection significantly increased rhizobacterial richness (ACE index, p < 0.05) and restructured the community composition, marked by enrichment of Paenibacillus (LDA score > 3.0). Procrustes analysis revealed tight coupling between microbial community shifts and metabolic reprogramming (M² = 0.446, p = 0.005), while Spearman correlations implicated pathogen-induced metabolites like geniposidic acid in recruiting beneficial Paenibacillus. Our results reveal that plant hosts dynamically secrete defense-related root metabolites to remodel the rhizosphere microbiome in response to P. brassicae infection. This dual-omics approach elucidates a chemical dialogue mediating plant–microbe–pathogen interactions, offering novel insights for engineering disease-suppressive microbiomes through root exudate manipulation.

Clubroot, incited by the obligate biotrophic protist Plasmodiophora brassicae, poses a severe threat to cruciferous crop production worldwide. Building on the concept of exogenous NLR protein delivery, we tested whether a bacterially expressed CRr protein (a recombinant Crr1a protein fused with an RXLR motif) could confer protection against clubroot in tumorous stem mustard (Brassica juncea var. tumida). Seedling roots were exposed to a crude lysate harboring the RXLR–Crr1a chimera, after which the fate of the protein and its downstream consequences were monitored across molecular, ecological, and metabolic levels. Time-resolved fluorescence imaging demonstrated that the recombinant signal became broadly distributed throughout the root system within a 24 h window, concomitant with a marked alleviation of disease severity. An empty vector control (equal protein, pET-28a(+) lysate) showed no significant protection versus the pathogen-only control (p > 0.05), suggesting that the observed protection is associated with the CRr protein lysate rather than general bacterial components. At the microbial level, the treatment fostered a more interconnected rhizosphere co-occurrence network and selectively promoted taxa, recognized as beneficial bacteria. At the metabolic level, several defense-associated compounds were elevated, among them jasmonic acid methyl ester, (2R)-2-hydroxyphenethylglucosinolate, 8-hydroxyluteolin 4′-methyl ether 8-glucuronide, and 4-hydroxyglucobrassicin. Furthermore, soil populations of beneficial bacteria including the Gram-positive genera Bacillus and Priestia exhibited strong positive associations with host defense metabolites. Collectively, these findings support a model in which externally supplied CRr protein lysate induces a response that can be observed at the metabolite and microbiome levels via rapid protein dissemination. This work lays a conceptual foundation for protein-based, microbiome-oriented management of soil-borne diseases without genetic modification of the crop.

Clubroot, caused by the obligate biotrophic protist Plasmodiophora brassicae, is a devastating soil-borne disease threatening global cruciferous crop production. To explore non-transgenic control strategies, this study investigated the efficacy of a crude protein extract containing RXLR motif-fused recombinant CRa protein against clubroot in tumorous stem mustard (Brassica juncea var. tumida) and its regulatory mechanisms in the rhizosphere. Mechanistically, fluorescence tracking confirmed that the CRa protein exploits the xylem stream for systemic translocation, colonizing the stele and vascular tissues within 24 h and significantly reducing the disease index. Ecologically, CRa protein reshaped the rhizosphere microbiome by enhancing α-diversity (Shannon and Simpson indices), increasing network complexity, and specifically enriching beneficial genera such as Pseudomonas. Metabolically, CRa protein induced the reprogramming of root exudates, upregulating defensive compounds including jasmonic acid methyl ester, 4-hydroxyglucobrassicin, and (2R)-2-hydroxy-2-phenethylglucosinolate. Overall, exogenous CRa protein activates a coordinated defense response through three key mechanisms: rapid vascular translocation, recruitment of beneficial microbiota, and metabolic reprogramming. This study provides novel insights for developing non-transgenic, microbiome-based green control strategies.