Transcriptome Analysis Of Acidovorax Citrulli--Cucumber Interaction And Preliminary Identification Of T3SE Genes In Acidovorax Citrulli

The bacterial fruit blotch(BFB)of cucurbits caused by Acidovorax citrulli(Ac)has severely affected the production of watermelons and other cucurbitaceous crops,causing huge economic losses.At present,the understanding of the pathogenic mechanism of Ac is extremely limited.Existing studies have found that type ? secretion effector(T3SE)secreted by the type ? secretion system(T3SS)are the key pathogenic factors in the pathogenic host process of Ac,but the research and understanding of T3SEs are still poor.Therefore,in this study,Ac FC440 strain was used as the research object to carry out the identification and functional analysis of T3SE in Ac.The main results are as follows:1.Transcriptome analysis of the interaction between Ac-cucumberThe result of transcriptome analysis of the interaction 48 h between Ac and 6 d`s cucumber cotyledons shows that the quality of transcriptome sequencing data of Ac and cucumber interaction was high.Quorum sensing correlated to the pathogenicity of FC440 strain in Ac.The main path that cucumber's defense reaction against to Ac infection is activated by Ca²⁺signal.PAL and GST play an important role in resistance of cucumber to Ac.This study lays the foundation for further exploration on the interaction mechanism between Ac and its host.2.Screening and preliminary identification of candidate T3SE genes in AcCombining the Ac FC440 strain genome database and the transcriptome database of Ac--cucumber interaction,20 candidate T3SE genes were obtained through bioinformatics analysis.Fce1-Fce10 was preliminarily identified as type ? effector protein in Ac.3.Preliminary analysis of the function of the candidate T3SE gene fce3 in AcBioinformatics analysis showed that Fce3 was type ? effector protein.The pathogenicity test results show that the fce3 mutant has significantly enhanced pathogenicity to the host,and can induce non-host hypersensitive response.This result shows that:Fce3 participates in the pathogenic mechanism of Ac to the host,and negatively regulates the pathogenicity.There is no obvious correlation between Fce3 and bacteria's extracellular secretase activity,biofilm formation ability and swimming ability.Fce3 did not inhibit the Bax-induced PCD response.These results suggest that Fce3may be a non-toxic protein involved in plant ETI immune signaling pathway.4.Preliminary analysis of the function of the candidate effector gene fce4 in AcBioinformatics analysis showed that Fce4 was type ? effector protein.The pathogenicity test results showed that the pathogenicity of the fce4 mutant to the host was significantly weakened,and can induce non-host hypersensitive response.This result shows that:Fce4 participates in the pathogenic mechanism of Ac to the host,and positively regulates the pathogenicity.There is no obvious correlation between Fce4 and bacteria's extracellular secretase activity,biofilm formation ability and swimming ability.Fce4 had the functional characteristics of the PCD reaction induced by Bax,indicating that Fce4 could inhibit the plant ETI reaction for toxic proteins.In conclusion,through transcriptome analysis of the interaction between Ac and cucumber,genes and metabolic pathways that play an important role in pathogen pathogenicity and host disease resistance were found in this study.The Fce1-Fce10 was identified as type ? effector protein in Ac.The expression of Fce3 and Fce4 could regulate the pathogenicity of Ac.The results of this study laid an important foundation for further analysis of the characteristics and pathogenic mechanism of T3ES in Ac.