The Different Responses Of Pectin Metabolism In Resistnt And Suceptible Banana (Musa Spp.AAA) To Foc4

Banana(Musa spp.)is one of the most important fruits in the tropical and subtropical regions.Banana Fusarium wilt is a soil-borne disease caused by Fusarium oxysporum f.sp.cubense(Foc),which seriously threatens the banana industry.In recent years,the technical application represented by the breeding of resistant cultivars and comprehensive control measures has reduced the degree of damage by banana Fusarium wilt.The research on the mechanism of banana disease resistance can provide a theoretical reference for the breeding of disease resistant varieties,and the cloning of resistant genes will provide materials for resistant breeding directly.The plant cell wall is an important place for the host to interact with the pathogen,and the cell wall pectin plays a major barrier in the process of invasion of the host by the pathogen.In the present study,‘Dong Jiao 1’(Musa spp.AAA)and its susceptible mutant ke2(Musa spp.AAA)against Fusarium oxysporum f.sp.cubense race 4(Foc4)at different developmental stages were used to analyze and compare the differences in the enzyme activities of pectin methylesterase(PME)and polygalacturonase(PG)in the hosts.In additional,differences in the spatial distribution and changes in the pectins with different degree of methylesterification as well as banana PME were investigated with immunofluorescence labelling method using monoclonal antibodies.Pectin metabolism-related genes were screened from the transcriptome database of ‘Dong Jiao 1’ and ke2 in response to Foc4 stress at inflorescence emerging plants.Gene cloning was also carried out with screened PMEs and PGs from both ‘Dong Jiao 1’ and ke2,respectively.The main results obtained are showed as follows: 1.The changes in PME and PG enzyme activities in banana roots after Foc4 infectionPathogen infections resulted in an increase of PME enzyme activity in the resistant cultivar and a decrease in the susceptible mutant ke2,independing on the developmental stages.Furthermore,the PME enzyme activity in both the control and pathoen-infected resistant plants was significantly higher than that of the susceptible mutant(except no significant difference at bagging stage).That indicates the PME enzyme activity in banana roots is related to its disease resistance.Relatively higher PME enzyme activity is beneficial to the degradation of cell wall pectin to oligogalacturonides,which could induce banana disease resistance.Similarly,pathogen infections resulted in an increase in the activity of PG enzymes in resistant cultivar,and a decrease in susceptible mutants.The difference was that the PG enzyme activity in the control resistant cultivar was equal to or lower than that of the susceptible mutant.2.The changes in PME and PG enzyme activities in banana leaf after Foc4 infectionUnder Foc4 stress,the activities of PME and PG in banana leaves were not completely consistent with the changes in roots.The PME and PG enzyme activities of the tissue cultured leaves showed no significant differences between the resistance and susceptibility materials,or the controls and pathogen infected treatments.On the contrary,at the bagging stage,the PME enzyme activity of the resistant cultivar ‘Dong Jiao 1’ was lower than that of the susceptible mutation ke2,both for the control and the pathogen infected treatment,while the PG enzyme activity was on the contrary.Pathogen infection resulted in higher emzyme activities except PME in the resistant cultivar.3.Temporal and spatial distribution and changes of cell wall pectin polysaccharideUnder Foc4 stress,the changes of cell wall pectin polysaccharide contents in the roots at different developmental stages were consistent well with those in the leaves.Pathogen infention resulted in an increase in the JIM5 antigen(low methyl esterification degree pectins)in the susceptible mutant ke2 but it was on the contrary for the resistant cultivar ‘Dong Jiao 1’.However,the content of high methylation degree pectins recognized by JIM7 antibody and PME expression level decreased in both ‘Dong Jiao 1’ and ke2 after infection.Decrease/increase in JIM5 antigen possibly was one of the typical responses of resistant /susceptible banana cultivars to Foc4.4.Screening of differentially expressed genes related to pectin metabolism in transcriptome databaseIn total,11 PME/PMEI and 13 PG genes were found to be differentially expressed in ‘Dong Jiao 1’ and ke2 after infected with Foc4.The 11 PME/PMEI genes were down-and up-regulated only in the susceptible ke2,and only one PME/PMEI gene was up-regulated in resistance and susceptibility materials.suggesting that PMEs/PMEIs were involved in the resistance of banana to Foc4.On the other hand,six and four PG genes were found to be up-and down regulated in the susceptible ke2,while it was one and two for resistant ‘Dong Jiao 1’.These results possibly suggested that PMEs were possible related to the susceptibility of banana to Foc4.5.Cloning of genes related to pectin metabolismA Ma PME8(GSMUA＿Achr7G15620＿001)gene and a Ma PG7(GSMUA＿Achr10G04160＿001)gene were cloned from ‘Dong Jiao 1’ and ke2,respectively.Amino acid sequence analysis showed that there were different three amino acids of Ma PME8 between ‘Dong Jiao 1’ and ke2.The Ma PG7 cloned from ‘Dong Jiao 1’ was exactly the same as that from ke2.