Cytological,Physiological And Biochemical And Transcriptomic Analyses Of Chinese Cabbage Response To Plasmodiophora Brassicae Infection

Clubroot is a global soil-borne disease caused by Plasmodiophora brassicae infecting Brassica crops,causing serious economic losses to cabbage and other Brassica crops.Analyzing the resistance mechanism of Clubroot and cultivating clubroot-resistant varieties is an effective way to reduce loss.In this study,clubrootresistant(DH40R)and clubroot-susceptible(DH199S)Chinese cabbage lines were used as experimental materials,and the resistance mechanism of Clubroot was analyzed through cytological observation,physiological and biochemical index determination and transcriptome analysis.The main results were as follows:1.The disease resistance and phenotype of 18 Chinese cabbage DH lines were investigated by the method of inoculating Plasmodiophora brassicae in the field,and a total of 10 high-susceptible clubroot and 8 immune-clubroot Chinese cabbage were obtained;combined with phenotypic investigation a pair of clubroot-resistant(DH40R)and clubroot-susceptible(DH199S)Chinese cabbage lines with little phenotypic difference were obtained.2.Through the dynamic observation of the cytology after the infection of Plasmodiophora brassicae,in both clubroot-resistant(DH40R)and clubrootsusceptible(DH199S)Chinese cabbage lines,the primary(root hair infection)and secondary infection(cortical infection)stages started 2 and 5 days after inoculation(dai),respectively.With the extension of the infection time,cortical infection was blocked and showed complete P.brassica resistance in DH40R;while disease scales of 1,2 and 3 were observed at 8,13 and 22 dai in DH199 S.3.At 2,5,8,13 and 22 dai,the physiological and biochemical indexes(defense enzymes,malondialdehyde,soluble sugar,and soluble protein)of the roots of the resistant and susceptible materials were measured,which showed that in the resistant materials catalase(CAT),superoxide dismutase(SOD),peroxidase(POD)activity,soluble sugar and soluble protein content increased significantly on the 8 dai(cortical infection period),which strongly resists the infection of P.brassicae.The content of malondialdehyde in the susceptible material began to rise sharply at 13 dai,indicating that the roots were severely damaged.4.Transcriptome analysis at 0,2,5,8,13 and 22 dai of the resistant and susceptible materials identified 3,851 differentially expressed genes(DEGs)between clubrootresistant(DH40R)and clubroot-susceptible(DH199S)Chinese cabbage lines.The analysis showed that: Genes related to auxin,disease-related proteins,disease-resistant proteins,cell wall tissue and biosynthesis,WRKY and MYB transcription factors are involved in the process of clubroot-resistant.5.Weighted gene coexpression network analysis(WGCNA)identified 3 gene modules that are highly related to clubroot resistance.Through the analysis of gene expression regulation in the modules,12 key genes for resistance to clubroot disease were screened.They are MYB44,AGP12,WRKY28,EIL3,ERF060,EXO,NHL13,LOX4,FMO,AOP1,POD56 and COMTL,these 12 genes work together to resist the infection of rhizobia,POD56 and AGP12 are the key genes for the next functional study.