Response Of Psl To Cucumber Defense And Mechanism Of Melatonin Alleviating Its Pathogenesis

Cucumber bacterial angular leaf spot(BALS)is caused by Pseudomonas syringae pv.lachrymans(Psl).The disease spread rapidly,and the yield of infected plants decreases seriously or even failed,which seriously affects cucumber production in China.Therefore,it is of great significance to study the response of Psl to cucumber defense and the induced resistance of cucumber by applying exogenous substances to control BALS.In this study,we analyzed the response of Psl to cucumber defense based on transcriptome and physiological methods,and explored the mechanism of melatonin(MT)in alleviating BALS.The main results are as follows:(1)Cucumber defense caused the expression of the 2475 differentially expressed genes(DEGs)in Psl,and these DEGs were mainly involved in NLR signaling,bacterial chemotaxis,quorum sensing,plant-pathogen interaction,and bacterial secretion system pathways.It was suggested that Psl used type III secretion system,chemotaxis to attack the host and escape from plant defense.(2)MT inhibited the growth of Psl,reduced the cell necrosis area of infected leaves,and alleviated BALS,and there was a dose effect.(3)Based on the transcriptome analysis of cucumber,MT treatment could induce cucumber resistance and enhance immunity in cucumber seedlings under normal conditions.After Psl invasion,MT alleviated BALS by preventing Psl invasion,activating plant signal transduction,inducing defense-related gene expression,and enhancing antioxidant and defense system activity(4)Pretreatment of MT enhanced the activities of antioxidant enzymes(superoxide dismutase,SOD;peroxidase,POD;catalase,CAT)and defense enzymes(phenylalanine ammonia-lyase,PAL;polyphenol oxidase,PPO);reduced the degree of stomatal opening;increased the intrinsic photochemical efficiency(Fv/Fm);electron transport rate(ETR);non-ohotochemical quenching confficient(NPQ).