Analysis Of Resistance Mechanism Of Mango To Bacterial Leaf Spot Based On Proteomics

Mango is known as ’ tropical fruit king ’ and is an important economic crop in China.Mango bacterial leaf spot caused by X.campestris pv.mangiferaeindicae seriously affects the appearance and commercial value of fruits,and hinders the production of mango greatly.Scientific research has confirmed that breeding resistant mango species was the most economical and effective strategy to prevent this disease.Therefore,analyzing the molecular mechanism of mango resistance to bacterial leaf spot will help accelerate the process of disease-resistant breeding.In our study,we used high-resistant and susceptible cultivars’ sick and healthy fruits to perform physiological and biochemical assay and proteomic study.To obtain hub-protein and explore the signal pathways that they may participate in,the WGCNA was used to combine representative biochemical data with proteomics for analysis.Finally,we analyzed the Nudix gene family of the hub-protein NUDT19.This study will further reveal the rearch of molecular mechanism of resistance to bacterial leaf spot in mango,and increase new high-quality gene resources for mango bacterial angular leaf spot resistance breeding.The results obtained are as follows:1.Effects of Xcm infection on physiological indexes related to mango resistance: The fruits of ’ Keitt ’ and ’ Renong No.1 ’ inoculated with Xcm and LB liquid medium at 0 d,2d and 6 d were used as experimental and control groups.We used the phloroglucinol method to dye the lignin near the mango inoculation point,it was found that the coloring depth and diffusion range of the two varieties of lignin increased with the inoculation time,and the global change was ’ Renong No.1 ’ > ’ Keitt ’.Compared with the non-inoculated treatment,the levels of POD,SOD,CAT and MDA of the two varieties increased,which increased by 92.67%,675.06%,135.32% and 27.06% in the resistant varieties,respectively.PPO activity increased by 71.08 % in susceptible varieties.PAL activity increased significantly with the delay of inoculation time in resistant varieties,and decreased slowly in susceptible varieties.POD,SOD,CAT and PAL activities were significantly different between the two varieties(P<0.01),while PPO activity and MDA content were not significantly different between the two varieties.Therefore,it is speculated that the changes of POD,SOD,PAL and CAT activities with variety response can be used as an auxiliary physiological index of mango resistance to bacterial leaf spot.2.Proteomic analysis of mango in response to Xcm infection: DIA quantitative proteomics technology was used to sequence the proteins of ’ Renong No.1 ’ and ’ Keitt ’on 0 d,2 d and 6 d after inoculation with Xcm and LB,then 8,775 proteins were obtained after filtering low-quality proteins.The protein set was classified into 18 modules using WGCNA.Trait module association showed that Green,Brown,Grey60 and Midnightblue were determined as the key modules.According to the visualization results of the protein interaction network in the module,a total of 40 hub-proteins were screened,including NUDT19,AAE1,PEX16,IDH1 and other proteins regulating cell redox homeostasis,At1g27190 and IAN9 two defensive proteins,GAPCp2,At4g26390,tal and other proteins involved in glycolysis,APP1,PYD1,MGL and other proteins involved in amino acid biosynthesis,DGK and APR9 two signal transduction proteins.Protein expression analysis showed that NUDT19,GAPCp2 and PYD1 were significantly up-regulated in’ Renong 1 ’,while the expression level in ’ Keitt ’ was relatively low.3.Analysis of mango Nudix gene family: A total of 9 Mi Nudix were identified using genome and proteome data.All Mi Nudixs contain three conserved domains(Motif1,Motif4,Motif5).Mi Nudix contain cis-acting elements(methyl jasmonate,gibberellin,and salicylic acid)that respond to hormones.The phylogenetic tree of Nudix gene family between mango and six common fruits was constructed,and it was found that Mi Nudix was closest to grape and sweet orange.After the mango was infected by Xcm,the results of protein sequencing showed that Mi Nudix6 was not expressed in the two varieties,Mi Nudix9 was specifically induced in the resistant variety ’ Renong No.1 ’,and the other seven Mi Nudixs were induced in both resistant and susceptible varieties.Mi Nudix3,Mi Nudix5,Mi Nudix7 and Mi Nudix8 expressed quite different among mango varieties.