| Ralstonia solanacearum species complex(RSSC)is rich in host diversity,among which R.pseudosolanacearum is the most widely distributed,and the plant bacterial wilt caused by this pathogen often causes great economic losses.In recent years,bacterial wilt of Cucurbitaceae crops has a tendency to gradually serious in a few regions of China.However,the pathogenicity of strains from different hosts to Cucurbitaceae and other families plants is unclear,and the mechanism of resistance of Cucurbitaceae plants to different pathogenic strains is not clear,it is difficult to make effective measures to control bacterial wilt of Cucurbitaceae crops.Our previous studies had confirmed that Cucurbitaceae crops such as pumpkin,towel gourd and balsam pear could occur bacterial wilt.In this study,the pathogenicity of 22 R.pseudosolanacearum stains from different hosts to three melon crops was determined,and the race was classified.The strains with different pathogenicity to pumpkin were screened,and the physiological and biochemical characteristics,transcriptome and metabolome of pumpkin plants inoculated with the strains were analyzed to reveal the resistance mechanism of pumpkin to different pathogenic strains.The main results were as follows:1.The pathogenicity of 22 strains from different hosts to pumpkin,towel gourd and balsam pear was determined.The results showed that Cucurbitaceae strains(Cq01,Bg07 and Tg03)and kidney bean strains(Kb01)had strong pathogenicity to the three melon crops,and five strains from tobacco,peanut and pepper had weak pathogenicity,but most of non Cucurbitaceae strains had no pathogenicity.The model strain GMI1000(Race 1)of RSSC was used to inoculated 8 plants based on wound root inoculated with bacterial suspension as reference,the races of 16 representative strains were determined,and it was found that these strains were all race 1.Five strains were inoculated into pumpkin plants with different concentrations by means of irrigating the roots with wound and inject bacterial suspension,and the strong pathogenic strain Cq01 and non pathogenic strain GMI1000 were screened out.One day after inoculation,bacteria were detected in the root system of both pumpkin plants inoculated with Cq01 and GMI1000 strain.Pumpkin inoculated with Cq01 strain 5 day and 7day,with the wilt incidence 30.56% and 77.78% respectively,while pumpkin plants inoculated with GMI1000 strain had not been infected.2.Both Cq01 and GMI1000 strains could induce reactive oxygen species and hypersensitive response in pumpkin,and the former was more intense.In pumpkin plants infected by Cq01 strain,the activities of phenylalnine ammonialyase(PAL),peroxidase(POD),superoxide dismutase(SOD)and polyphenol oxidase(PPO)were significantly increased from the early stage of infection to the middle stage of infection,and the production of malondialdehyde(MAD)was also promoted.GMI1000 strain could also significantly enhance POD activity in pumpkin plants,but it was significantly lower than that of Cq01 treatment.GMI1000 could only enhance the activities of PAL,SOD and PPO in pumpkin plants at the early stage of infection,and could not promote the production of MAD.The results showed that the activities of PAL,POD,SOD,PPO and the content of MAD in pumpkin plants inoculated with bacteria were related to the virulence of the bacteria.3.Transcriptome analysis of pumpkin in response to infection by strains Cq01 and GMI1000 showed that there were 146 differentially expressed genes in pumpkin plants inoculated with Cq01 strain,and 110 genes were up-regulated.GO annotation of differentially expressed genes is mainly enriched in ethylene-activated signaling pathway,jasmonic acid mediated signaling pathway,defense response to bacterium,response to salicylic acid and pectin catabolic process,etc.KEGG annotation is mainly enriched in pectate lyase related to plant cell wall degradation,calcium-binding protein and ethylene-responsive transcription factor 1 related to signal transduction,RPM1-interacting protein 4,transcription factor MYB and EREBP-like factor related to disease resistance,and acetylornithine deacetylase related to amino acid synthesis,etc.There were 53 differentially expressed genes and 49 up-regulated genes in pumpkin plants inoculated with GMI1000.GO annotation of differentially expressed genes is mainly enriched in nitrate assimilation,oligopeptide transport,nitrate transport,and plant-type cell wall organization,etc.KEGG annotation is mainly enriched in Pathogenesis-related protein 1,cinnamyl-alcohol dehydrogenase and beta-glucosidase related to pentose phosphate,glutathione S-transferase and glutaredoxin related to antioxidation,fructose-1,6-bisphosphatase I related to energy metabolism,and nitrate/nitrite transporter related to nitrogen metabolism,etc.Eight genes of Cq01 and GMI1000 interacting with host were selected for q RT-PCR verification,and the results were basically consistent with the results of transcriptome sequencing.4.The results of metabolome analysis of pumpkin response to Cq01 and GMI1000 infection showed that there were three different metabolites(ornithine,D-erythronolactone and threonic acid)in pumpkin plants inoculated with Cq01 strain,which were all up-regulated.There were three different metabolites in pumpkin plants inoculated with GMI1000 strain,gluconic acid was up-regulated,raffinose and 1,3-Diaminopropane were down-regulated.The results of transcriptome and metabolome association analysis showed that arginine biosynthesis pathway was the closest metabolic pathway in response to Cq01 infection,and pentose phosphate pathway was the closest metabolic pathway in response to GMI1000 infection.In summary,Cucurbitaceae and a few non-Cucurbitaceae strains showed pathogenicity to cucurbitaceae plant,while most non-cucurbitaceae strains showed no pathogenicity.Defense related physiological and biochemical reactions induced by Cq01 strain were stronger than those induced by GMI1000 strain.According to the results of transcriptome and metabolome association analysis in response to the infection of Cq01 and GMI1000 strains in pumpkin,it was speculated that ornithine metabolites were produced in the pumpkin plants infected by Cq01 strain through the arginine biosynthesis pathway,which reduced the resistance of the plant to bacterial wilt and led to plant disease,while GMI1000 strain could induce the production of disease-resistant substances by enhancing the pentose phosphate pathway in pumpkin plant,which inhibited the expansion of the bacteria in the plant and prevented the plant from being harmed by the bacteria. |
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