Effector proteins secreted by pathogens play critical roles in suppressing host immunity and facilitating infection. In this study, we identified and characterized the putative disulfide-isomerase effector protein Pb001683 from the clubroot pathogen Plasmodiophora brassicae, a major threat to cruciferous crops. Transgenic plants overexpressing Pb001683 exhibited increased susceptibility to P. brassicae, supporting its role in pathogenicity. Subcellular localization analysis showed that Pb001683 was localized in the endoplasmic reticulum (ER) and nucleus in host cells. Co-immunoprecipitation coupled with mass spectrometry (CoIP-MS) analysis identified 353 candidate host proteins associated with Pb001683, suggesting a broad network of potential host targets. Gene Ontology (GO) enrichment indicated that these proteins were enriched in processes such as carboxylic acid metabolic process and oxoacid metabolic process. The interaction between Pb001683 and BrCYP83A1 was further validated using the split-luciferase assay. In addition, reactive oxygen species (ROS) assays showed that Pb001683-overexpressing plants exhibited elevated ROS levels compared with the control. Collectively, these findings provide new insights into the molecular mechanisms of clubroot pathogenesis and highlight potential strategies for enhancing crop resistance by targeting effector-host interactions.

BrRLP1 positively regulates the resistance to downy mildew in Brassica rapa by interacting with the monodehydroascorbate reductase BrMDAR1. Downy mildew is a devastating disease that severely affects the yield and quality in Brassica rapa. Receptor-like protein (RLP) is important for plants disease-resistant response. Here, a new downy mildew resistance gene, BrRLP1, was identified in Brassica rapa through GWAS analysis and QTL mapping. BrRLP1 encodes a membrane-localized receptor-like protein, and its expression level showed significant differences in the resistant and susceptible materials after inoculation with downy mildew. Transient expression and transgenic functional verification revealed that BrRLP1 is a positive regulator for the downy mildew resistance. All the BrRLP1R overexpressed plants exhibited a high-resistance phenotype to downy mildew after inoculation. Haplotype analysis revealed that the SNP309 in the LRR domain of BrRLP1 is a key functional site for the resistance difference to downy mildew. Y2H and LCI assays showed that BrRLP1 can interact with the monodehydroascorbate reductase BrMDAR1, which is involved in the ascorbic acid metabolic pathway. Our results revealed the function of BrRLP1 in regulation of downy mildew resistance by interacting with BrMDAR1, which provides new insight into the molecular mechanism underlying disease resistance immune response in Brassica rapa.

Chinese cabbage (Brassica rapa ssp. pekinensis) is a key leafy vegetable crop across Asian. In recent years, premature bolting has been exacerbated by global climate change and off-season cultivation practices. Chinese cabbage (Brassica rapa ssp. pekinensis) is a key leafy vegetable crop across Asia. Premature flowering frequently occurs under abiotic stresses, while parallel growth retardation significantly reduces plant yield. Here we showed that overexpression of BrHIS4.A04 significantly accelerated flowering, mediated by upregulation of FT1 and SOC1 alongside suppression of FLC homologs. This genetic reprogramming, however, increases drought susceptibility through concurrent downregulation of stress-responsive genes. Mechanistically, BrHIS4.A04 triggered ROS biosynthesis, while pharmacological inhibition of ROS delayed flowering specifically in overexpression lines. Notably, BrHIS4.A04 overexpression suppressed a key regulatory network governing cell proliferation, including downregulation of TCP14/TCP24, SDD1, and six other genes critical for cell cycle progression and meristem activity. This suppression led to reduced rosette diameter, plant height, and leaf number, culminating in a decrease in biomass. Collectively, our findings reveal a histone protein that integrates redox signaling and cell cycle regulation to orchestrate developmental transitions, offering insights for crop improvement strategies targeting flowering time and yield stability.

Choy Sum (Brassica rapa subsp. chinensis var. parachinensis), also known as flowering Chinese cabbage, is an important stalk vegetable in Asia. However, the unique regulatory mechanism governing its "easy-bolting yet susceptible to premature bolting" trait remains poorly understood. The phosphatidyl ethanolamine-binding protein (PEBP) family serves as a central regulator of bolting, flowering, and growth development in plants. But this gene family has not been systematically identified and studied in Choy Sum yet. Therefore, this study systematically identified and analyzed the members of the PEBP gene family in Choy Sum using bioinformatics, transcriptomics, real-time fluorescence quantification, subcellular localization, and transgenic techniques. A total of 12 BcPEBP genes were identified and categorized into three subfamilies: FT-like, TFL1-like, and MFT-like. Phylogenomic analyses revealed family expansion through whole-genome duplication with strong purifying selection. Most members have highly conserved core motifs and gene structures. Protein sequence alignment showed that BcFT-2 and BcTFL-2 underwent non-synonymous mutations at key residues. The analysis of cis-acting elements suggests that the BcPEBP gene may be influenced by complex hormone and light regulatory networks. Expression profiling demonstrated leaf-specific upregulation of BcFT-1/2 during development and shoot apices-predominant expression of BcTFL1 genes, and the expression between homologous genes of BcTFL1-1/3 is more refined. Subcellular localization confirmed dual nuclear and plasma membrane targeting of BcFT-1/2 proteins. Overexpression of BcFT-1/2 in transgenic Arabidopsis promotes flowering. These findings establish BcPEBP genes as key bolting regulators and provide molecular targets for breeding-improved varieties.

Introduction:Brassica rapa plants often face combined or sequential abiotic stresses, but the potential negative association between salt/drought tolerance and thermotolerance remains poorly understood. Most studies have focused on individual stress responses, leaving the regulatory networks that may constrain broad-spectrum resilience largely unexplored. Methods:Here, we propose a hormone- and anthocyanin-centered framework for understanding this apparent negative association in B. rapa, based on integrated physiological, transcriptomic, hormonal and metabolic analyses across diverse inbred lines. Results:Physiological characterization of 11 lines revealed an apparent negative association (salt vs. heat: r = -0.555; drought vs. heat: r = -0.339). Time-resolved transcriptomics uncovered stress-specific temporal patterns: a triphasic response under salt stress, a 'rapid response-readjustment-reactivation' pattern under drought, and a biphasic mechanism under heat stress. Hormonal profiling identified ABA and ethylene biosynthesis-related metabolites as correlates of osmotic adaptation. The chalcone synthase gene BraA10g024990.3C (CHS) showed genotype- and stress-specific expression and correlated with anthocyanin accumulation. Exogenous hormone treatments indicated that ABA and ethylene induce, while GA represses, CHS-mediated anthocyanin production. Discussion:Despite the correlative nature of these data, this study provides a candidate regulatory axis and suggests that hormone-directed anthocyanin metabolism may contribute to the negative association between osmotic tolerance and thermotolerance in B. rapa, offering targets for breeding multi-stress-resilient crops.

Downy mildew, caused by the biotrophic oomycete Hyaloperonospora parasitica, is one of the most devastating diseases affecting global Brassica production. Despite its significant impact, the molecular and cellular mechanisms underlying both compatible and incompatible interactions of H. parasitica and Brassica rapa remain poorly understood. In this study, we identified an H. parasitica RXLR effector, DM459, which demonstrates the ability to induce autophagy by targeting BraATG8i, a key component of autophagosome formation, as confirmed by multiple in vivo and in vitro assays. BraATG8i is a positive regulator of defense against downy mildew, which was determined by the BraATG8i overexpression and RNA interference in B. rapa. Furthermore, the effector DM459 interacts with BraATG8i as well as BraATG4, BraATG3, and BraATG7-core proteins required for autophagosome assembly. This interaction-enhanced autophagy contributed to elevated disease resistance. Moreover, pathogen inoculation or DM459 presence stimulated salicylic acid (SA) biosynthesis, which in turn activated BraATG8i expression and further elevated autophagy. Collectively, our results demonstrated that the effector DM459 triggers autophagy by directly targeting BraATG proteins and simultaneously activates SA signaling, which consequently enhances plant resistance to downy mildew.

Brassica rapa is one of the most important vegetable crops with the largest cultivation area in China. Compared with other genotyping technologies, the Affymetrix Axiom genotyping with single nucleotide polymorphism (SNP) array has become popular due to its high-throughput, flexibility, and efficiency. In this study, we successfully developed the first SNP14K array for B. rapa based on resequencing data from 189 accessions. The array contains 148,399 high-quality SNPs evenly distributed across the genome. Minor Allele Frequency (MAF) analysis indicated that these SNPs are highly polymorphic. Principal component analysis (PCA) clearly distinguished different subspecies among the 189 ​B. rapa accessions. Population structure and phylogenetic analyses demonstrated that the 148,399 high-quality SNPs are representative. Next, we assessed the genetic relationships of 97 ​B. rapa varieties using the SNP14K array on the Axiom genotyping system. Phylogenetic analysis showed that these 97 cultivars were divided into seven distinct subpopulations: Chinese cabbage, Pak choi, Wawacai, Baibangkuaicai, Qingbangkuaicai, Caixin, and one mixed type. In addition, major quantitative trait loci (QTLs) related to leaf trichome and flowering time were accurately identified using the SNP14K array. This newly developed SNP14K array provides a valuable tool for genetic diversity analysis, gene/QTL mapping, and molecular breeding in B. rapa.

Postharvest leaf senescence is a pivotal determinant influencing the quality and shelf life of leafy vegetables, exemplified by pak choi (Brassica rapa L. subsp. chinensis). While the regulatory role of gibberellin (GA) in modulating leaf senescence has been documented across diverse plant species, the underlying physiological and molecular mechanisms remain insufficiently characterized. This study, through a combination of transcriptomic and metabolomic analyses, investigated the effect of exogenous GA on postharvest leaf senescence in pak choi. GA treatment alleviated etiolation, maintained chlorophyll levels, reduced conductivity and malondialdehyde content, and delayed the onset of senescence symptoms in postharvest pak choi. Transcriptome profiling indicated that GA suppressed the expression of the senescence-associated genes BraSRGs and BraSAGs. In addition, GA influenced chlorophyll degradation and preserved chlorophyll content by modulating the expression of genes implicated in chlorophyll metabolism, including BraPPH, BraSGR1, BraNYCI, and BraPAO. GA treatment impacted lipid levels and regulated the degradation of membrane phospholipids. Furthermore, exogenous GA treatment disrupted the efficacy of the jasmonic acid signal pathway, primarily through the transcriptional downregulation of key regulatory genes, including BraJAZ10 and BraJAR1. These results provide insights into the role of GA in delaying postharvest leaf senescence and highlight potential targets for improving postharvest management in leafy vegetables.

Chinese cabbage production faces critical mechanization challenges due to traditional plant architectures that limit mechanical harvesting efficiency. Traditional breeding prioritized short-hypocotyl varieties to prevent damping-off, but long hypocotyls are now critical for mechanical harvesting. We identified BrHB52, an HD-Zip transcription factor, as a key regulator of hypocotyl elongation through quantitative trait locus (QTL) mapping, RNA-seq, and haplotype analysis. BrHB52 expression was significantly higher in the long-hypocotyl variety R031L than in the short-hypocotyl variety R032S. Overexpression of BrHB52 in both Chinese cabbage and Arabidopsis led to elongated hypocotyls. The silencing of BrHB52 in R031L resulted in a reduction of hypocotyl length. Sequence alignment revealed a 251-bp insertion in the BrHB52 promoter of the long-hypocotyl variety R031L, which introduced the light-responsive GT-1 motifs. The upstream transcription factors Phytochrome-interacting factor4 (PIF4) and B-box zinc finger 24 (BBX24) were identified through yeast one-hybrid screening using the BrHB52 R031L promoter sequence. PIF4 were found to bind to the both BrHB52 R031L and BrHB52 R032S promoters and activate their expression through G-box, while light-induced factor BBX24 only bind to the BrHB52 R031L promoter and activate its expression by light-responsive element GT-1. Our findings elucidate a BrPIF4/BrBBX24-BrHB52 regulatory module that controls plant architecture through hypocotyl elongation. These findings not only provide critical genetic targets for developing mechanization-compatible Chinese cabbage, but also develop transgenic prototypes with elongated hypocotyls, offering practical resources for mechanized breeding.

Pathogens significantly restrict the production of Brassica rapa (B. rapa L. ssp. Pekinensis), with climate change and evolving planting patterns exacerbating disease prevalence. Multichannel rapid diagnostic methods in the field can facilitate the early detection and control of diseases in B. rapa. Here, we established a multichannel lateral flow biosensor (LFB) combined with a CRISPR/Cas12a cleavage assay for the simultaneous detection of four B. rapa diseases. Key innovations of this study include: (1) High specificity and sensitivity, down to pathogen concentrations of 1.5 pg/mu l-due to the optimization of crRNA secondary structure: the more stable the crRNA, the higher its detection sensitivity. (2) Optimized visual detection parameters. We identified ideal concentration ratios for the visual fluorescence detection system: 50 nM Cas12a, 50 nM crRNA, and 500 nM ssDNA fluorescent probe. Furthermore, the optimal concentrations of components on the LFB detection system were 3 mu l SA-GNPs, 500 nM ssDNA test strip probe, 0.5 mg/ml biotin-BSA as the test line, and 1 mg/ml anti-FITC as the control line. (3) Field-Ready Cas-AIRPA Platform. We developed the on-site Cas-AIRPA platform for the simultaneous detection of B. rapa pathogens by combining rapid nucleic acid extraction and a four-channel lateral flow biosensor (4-LFB), which quickly provides disease-related information through a specific 2D barcode. Analysis of B. rapa samples in the field confirmed the suitability of the Cas-AIRPA platform for rapid (similar to 25 min) and simultaneous on-site detection of four diseases of B. rapa. This platform can also be adapted to detect other plant diseases in the field.

The soil-resident pathogen, Plasmodiophora brassicae, infects cruciferous crops, causing obligate parasitic clubroot disease and posing a significant threat to the Brassica vegetable industry in China. To learn more about its pathogenesis, we reported a Nanopore sequencing-derived 25.3 Mb high-quality genome sequence of P. brassicae pathotype 4 strain (P.b 4). Comparing the P.b 4 genome with that of the published P. brassicae e3 genome (P.b e3) identified single nucleotide polymorphisms, structural variations, and small insertions and deletions. We then carried out RNA-sequencing of root samples from a clubroot-susceptible line at 5, 14, and 28 days after inoculation (DAI), and classified genes into five categories based on their expression patterns. Interestingly, 158 genes were highly expressed at 14 DAI, which were enriched in budding cell isotropic bud growth, ascospore wall assembly, spore wall assembly, spore wall biogenesis, and ascospore wall biogenesis. Subsequently, we bioinformatically predicted 555 secreted effector candidates, among which only 125 were expressed during infection and had amino acid lengths less than 400. The putative effector Pb010018, which was highly expressed at 14 DAI, was validated to have a signal peptide using a yeast secretion system. Luciferase activity and co-immunoprecipitation assays demonstrated that Pb010018 interacts with serine hydroxymethyltransferase BrSHMT1, and expression analysis showed that SHMT1 was upregulated in both Arabidopsis and B. rapa during infection. Furthermore, after infection, the Arabidopsis shmt1 mutant (atshmt1) showed reduced severity of clubroot disease, together with downregulated expression of Pb010018. Our results offer new insights into plant-pathogen interaction mechanisms, and provide the possibility for improving Brassica resistance to clubroot disease.

Downy mildew is a major disease that significantly impacts the yield and quality of Brassica rapa. While histone deacetylase (HDAC) family members are implicated in stress responses, their role in regulating downy mildew resistance in B. rapa remains unclear. Herein, we treated the susceptible B. rapa line R32 with Trichostatin A (TSA), a potent HDAC inhibitor. Notably, TSA application significantly enhanced the susceptibility of B. rapa seedlings to downy mildew infection, demonstrating that HDAC plays a crucial role in mediating resistance against this pathogen. Subsequently, we conducted phylogenetic analysis of HDAC family members and performed high-throughput sequencing to assess HDAC gene expression patterns in the resistant (R31) and susceptible (R32) lines following downy mildew inoculation. Notably, the expression of BrHDA6 was significantly higher in the resistant line R31 compared to the susceptible line R32, suggesting its potential role in disease resistance. Using a genetic transformation system, we generated stable transgenic B. rapa plants overexpressing or silenced for BrHDA6. Inoculation with the downy mildew pathogen revealed that BrHDA6 positively regulates disease resistance. Modification omics and parallel reaction monitoring analysis demonstrated that BrHDA6 directly reduces the acetylation level of sulphotransferase 12 (BrSOT12), which likely enhances sulfotransferase activity, consequently boosting salicylic acid production during downy mildew infection. Interaction between BrHDA6 and BrSOT12 was further validated through yeast two-hybrid and dual-luciferase assays. Our study reveals that BrHDA6 confers downy mildew resistance in B. rapa through nonhistone protein deacetylation of BrSOT12, uncovering a novel regulatory mechanism in plant-pathogen interactions.

The diversity in alternative splicing of long noncoding RNAs (lncRNAs) poses a challenge for functional annotation of lncRNAs. Moreover, little is known on the effects of alternatively spliced lncRNAs on crop yield. In this study, we cloned nine isoforms resulting from the alternative splicing of the lncRNA LAIR in rice. The LAIR isoforms are generated via alternative 5 '/3 ' splice sites and different combinations of specific introns. All LAIR isoforms activate the expression of the neighboring LRK1 gene and enhance yield-related rice traits. In addition, there are slight differences in the binding ability of LAIR isoforms to the epigenetic modification-related proteins OsMOF and OsWDR5, which affect the enrichment of H4K16ac and H3K4me3 at the LRK1 locus, and consequently fine-tune the regulation of LRK1 expression and yield-related traits. These differences in binding may be caused by polymorphic changes to the RNA secondary structure resulting from alternative splicing. It was also observed that the composition of LAIR isoforms was sensitive to abiotic stress. These findings suggest that the alternative splicing of LAIR leads to the formation of a functional transcript population that precisely regulates yield-related gene expression, which may be relevant for phenotypic polymorphism-based crop breeding under changing environmental conditions.

Global warming has a severe impact on the flowering time and yield of crops. Histone modifications have been well-documented for their roles in enabling plant plasticity in ambient temperature. However, the factor modulating histone modifications and their involvement in habitat adaptation have remained elusive. In this study, through genome-wide pattern analysis and quantitative-trait-locus (QTL) mapping, we reveal that BrJMJ18 is a candidate gene for a QTL regulating thermotolerance in thermotolerant B. rapa subsp. chinensis var. parachinensis (or Caixin, abbreviated to Par). BrJMJ18 encodes an H3K36me2/3 Jumonji demethylase that remodels H3K36 methylation across the genome. We demonstrate that the BrJMJ18 allele from Par (BrJMJ18(Par)) influences flowering time and plant growth in a temperature-dependent manner via characterizing overexpression and CRISPR/Cas9 mutant plants. We further show that overexpression of BrJMJ18(Par) can modulate the expression of BrFLC3, one of the five BrFLC orthologs. Furthermore, ChIP-seq and transcriptome data reveal that BrJMJ18(Par) can regulate chlorophyll biosynthesis under high temperatures. We also demonstrate that three amino acid mutations may account for function differences in BrJMJ18 between subspecies. Based on these findings, we propose a working model in which an H3K36me2/3 demethylase, while not affecting agronomic traits under normal conditions, can enhance resilience under heat stress in Brassica rapa.

Turnip mosaic virus （TuMV） constitutes one of the primary diseases affecting Brassica rapa,severely impacting its production and resulting in crop failures in various regions worldwide.Recent research has demonstrated the significance of plant translation initiation factors,specifically the eIF4E and eIF4G family genes,as essential recessive disease resistance genes.In our study,we conducted evolutionary and gene expression studies,leading us to identify e IF（iso）4E.c as a potential TuMV-resistant gene.Leveraging CRISPR/Cas9 technology,we obtained mutant B.rapa plants with edited eIF（iso）4E.c gene.We confirmed eIF（iso）4E.c confers resistance against TuMV through phenotypic observations and virus content evaluations.Furthermore,we employed ribosome profiling assays on eif（iso）4e.c mutant seedlings to unravel the translation landscape in response to TuMV.Interestingly,we observed a moderate correlation between the fold changes in gene expression at the transcriptional and translational levels （R 2 =0.729）.Comparative analysis of ribosome profiling and RNA-seq data revealed that plant-pathogen interaction,and MAPK signaling pathway-plant pathways were involved in eIF（iso）4E.c-mediated TuMV resistance.Further analysis revealed that sequence features,coding sequence length,and normalized minimal free energy,influenced the translation efficiency of genes.Our study highlights that the loss of e IF（iso）4E.c can result in a highly intricate translation mechanism,acting synergistically with transcription to confer resistance against TuMV.

ABSTRACTThe senescence of leafy vegetables is inherent and general after harvest. DNA methylation affects the senescence process of plant leaves. Limited studies have explored the impact of exogenous methylation inhibitors on postharvest vegetables and the mechanisms of their effects on the transcriptome and metabolome during storage. In this study, pak choi was immersed in 100 mg L−1 of 5‐azacytidine (AZ) (an inhibitor of methyltransferase) solutions, indicated that AZ yielded significant acceleration in leaf senescence. Compared to the control group, the AZ‐treated pak choi exhibited faster weight loss, higher malondialdehyde content, greater color change, and higher chlorophyllase activity. Transcriptomic and widely targeted metabolomic analyses were then performed on pak choi samples. Transcriptomic investigation disclosed that the chlorophyll degradation genes BraSGR2 and BraPPH were upregulated by AZ, leading to the degradation of more chlorophyll content. AZ effectively stimulated upregulation of the senescence‐associated genes (BraSAG20, BraSAG21, BraSRG1, and BraSRG2), thereby accelerating the pace of the senescence process. The widely targeted metabolomic analyses demonstrated that AZ downregulated the flavonoid synthase genes BraFLS1 and BraF3H, causing a relative decline in flavonoid levels. The study also unveiled a diminution in carbohydrate content during storage, further exacerbated by AZ. To encapsulate, our preliminary findings suggest that the application of AZ effectively accelerates the process of leaf senescence in stored pak choi, which helps us understand the relationship between DNA demethylation and vegetable senescence.

In four rice genomes, 85 ABC1-family genes were identified by comparative genomics, evolution, genetics, and physiology. One, OsABC1-13, was shown by knockdown and knockout experiments to affect plant height, grain size, and photosynthetic capability.

Amylose content (AC) is the main factor determining the palatability, viscosity, transparency, and digestibility of rice (Oryza sativa) grains. AC in rice grains is mainly controlled by different alleles of the Waxy (Wx) gene. The AP2/EREBP transcription factor OsEBP89 interacts with the MYC-like protein OsBP5 to synergistically regulate the expression of Wx. Here, we determined that the GLYCOGEN SYNTHASE KINASE 5 (OsGSK5, also named SHAGGY-like kinase 41 [OsSK41]) inhibits the transcriptional activation activity of OsEBP89 in rice grains during amylose biosynthesis. The loss of OsSK41 function enhanced Wx expression and increased AC in rice grains. By contrast, the loss of function of OsEBP89 reduced Wx expression and decreased AC in rice grains. OsSK41 interacts with OsEBP89 and phosphorylates four of its sites (Thr-28, Thr-30, Ser-238, and Thr-257), which makes OsEBP89 unstable and attenuates its interaction with OsBP5. Wx promoter activity was relatively weak when regulated by the phosphomimic variant OsEBP89E -OsBP5 but relatively strong when regulated by the nonphosphorylatable variant OsEBP89A -OsBP5. Therefore, OsSK41-mediated phosphorylation of OsEBP89 represents an additional layer of complexity in the regulation of amylose biosynthesis during rice grain development. In addition, our findings provide four possible sites for regulating rice grain AC via precise gene editing.

Increasing plant resistance to Verticillium wilt (VW), which causes massive losses of Brassica rapa crops, is a challenge worldwide. However, few causal genes for VW resistance have been identified by forward genetic approaches, resulting in limited application in breeding. We combine a genome-wide association study in a natural population and quantitative trait locus mapping in an F2 population and identify that the MYB transcription factor BrMYB108 regulates plant resistance to VW. A 179 bp insertion in the BrMYB108 promoter alters its expression pattern during Verticillium longisporum (VL) infection. High BrMYB108 expression leads to high VL resistance, which is confirmed by disease resistance tests using BrMYB108 overexpression and loss-of-function mutants. Furthermore, we verify that BrMYB108 confers VL resistance by regulating reactive oxygen species (ROS) generation through binding to the promoters of respiratory burst oxidase genes (Rboh). A loss-of-function mutant of AtRbohF in Arabidopsis shows significant susceptibility to VL. Thus, BrMYB108 and its target ROS genes could be used as targets for genetic engineering for VL resistance of B. rapa.

The plant cell wall is the first line of defence against physical damage and pathogen attack. Wall-associated kinase (WAK) has the ability to perceive the changes in the cell wall matrix and transform signals into the cytoplasm, being involved in plant development and the defence response. Downy mildew, caused by Hyaloperonospora brassicae, can result in a massive loss in Chinese cabbage (Brassica rapa L. ssp. pekinensis) production. Herein, we identified a candidate resistant WAK gene, BrWAK1, in a major resistant quantitative trait locus, using a double haploid population derived from resistant inbred line T12-19 and the susceptible line 91-112. The expression of BrWAK1 could be induced by salicylic acid and pathogen inoculation. Expression of BrWAK1 in 91-112 could significantly enhance resistance to the pathogen, while truncating BrWAK1 in T12-19 increased disease susceptibility. Variation in the extracellular galacturonan binding (GUB) domain of BrWAK1 was found to mainly confer resistance to downy mildew in T12-19. Moreover, BrWAK1 was proved to interact with BrBAK1 (brassinosteroid insensitive 1 associated kinase), resulting in the activation of the downstream mitogen-activated protein kinase (MAPK) cascade to trigger the defence response. BrWAK1 is the first identified and thoroughly characterized WAK gene conferring disease resistance in Chinese cabbage, and the plant biomass is not significantly influenced by BrWAK1, which will greatly accelerate Chinese cabbage breeding for downy mildew resistance.