Biocontrol Against Wheat Diseases Caused By Fusarium Graminearum And Mechanisms Study

Fungal diseases on wheat cause heavy loss on gloable food production.Biocontrol,as an environmental friendly control strategy against plant diseases,attracts lots of attentions around the world.However,no attempt has been conducted on screening BCAs against several diseases occurred on same plant.In this study,we first isolated 966 bacterial strains from different part of wheat,of which potential biocontrol values were detected according to their abilities in antagonism inhibition and secreting extracellular hydrolytic enzyme.As our aim is to control fusarium head blight and fusarium root rot at the same time,slight modifications were applied on the previous assessing strategy.Finally,37 bacterial strains with good assessing results were tested in both green chamber and field biocontrol tests,and 10 of them showed high biocontrol efficacy against fusarium head blight and fusarium root rot.Statistically,the correlation coefficient between green chamber test results and assessing results is 0.720 and between field test results and assessing results is 0.806,which means our modified assessing method is applicable in this study.Furthermore,we also studied one Bacillus subtilis strain BsEl,which displayed high biocontrol efficacy against fusarium root rot(62.14%)while it does no have antagonism ability against the pathogen fungi or extracellular hydrolytic enzyme secretion ability.The y-PGA production ability of BsEl has been proved to be one of the major factors that conducted to its biocontrol efficacy.To further study the biocontrol mechanism mediated by Bacillus spp.,we got into the aspect of bacterial secretion system,especially the bacterial type IV secretion system(T4SS).The analysis of genome sequence of B.cereus AR156 reveal that it has one set of virulence protein coding sequence.We also studied the mechanisms of the protein interaction between T4SS effector VirE2 and Arobidopsis VIP1.1.Conjunctively screening BCAs against fusarium head blight and fusarium root rot.Fusarium graminearum can cause fungal disease in different growth periods of wheat.Our study is aiming to screening BCAs with potential biocontrol capacity against fusarium head blight and fusarium root rot from different part of wheat tissue.Totally 966 bacterial strains were proceeded by antagonism test against F.graminearum and extracellular hydrolytic enzyme tests,etc.,cellulase,chitinase,glucanase,protease and siderophores.37 bacterial strains with potential biocontrol efficacy were selected for further bicocontrol assay against fusarium root rot in green chamber and fusarium head blight in field.Total of 8 bacterial strains displayed more than 40%biocontrol efficacy in green chamber test against fusarium root rot and 3 in field test against fusarium head blight.Our results also confirmed the revised BCAs assessing strategy,which has acceptable correlation coefficient in green chamber and field biocontrol assays(0.720 and 0.806).We also found B.cereus AR156 treated wheat plants showed biocontrol efficacy against wheat head blight by 42.63%and wheat root rot by 45.22%.2.Study of function of y-PGA in biocontrol against fusarium root rot mediated by Bacillus subtillis BsEl.In previous study,one B.subtillis strain BsEl displays 62.14%biocontrol efficacy against fusarium root rot under green chamber condition.We tried to associate y-PGA productivity of BsEl and its biocontrol efficacy.The PGA productivity was impaired after knock-out of gene pgsB(PGA-synthase-CapB).ApgsB mutant strain also showed decreased motile ability on soild surface,lower colonization ability on wheat root system and biocontrol efficacy against fusarium root rot compared with wildtype BsEl.Moreover,these decreases were complemented by complementing pgsB back to ApgsB mutant,and these indicators were increased after two y-PGA degradation enzyme coding gene pgdS and ggt were knocked out from wildtype BsEl.Next we examined the gene level changes on wheat tissue after treated by BsE1.The ROS(Reactive oxygen species)related genes were delayed in expression level and phytoalexin related genes were induced in expression level 48 hours after BsEl treatment,which indicate BsEl might increase resistance against fungi infection on wheat.3.Interaction between bacterial T4SS effector VirE2 and homologues of Arabidopsis VIP1.Bacterial T4SS(Type IV secretion system)is a special bacterial machinery for transferring single-strand DNA(ssDNA)and protein effectors in to target cell.A set of T4SS related virulence protein homologues coding sequences were acquired,after analysis of whole genome sequencing data of B.cereus AR156,which is an effective biocontrol B.cereus strain.In previous study,bacterial T4SS related effector VirE2 was reported to bind Arabidopsis VIP1 and VIP1,as a member of plant bZIPs family proteins,was suggested to be an adaptor between VirE2 and several host cell proteins,and probably helping nuclear localization of VirE2 and the T-DNA integration into host genome.AR156 coding BcVirE2 was shown the interaction with Arabidopsis VIP1 and its homologue in T.aestivum named TaFD-like 2.Our study found the interaction between VirE2 and VIP1 could be extended to VIP1 homologues in different plant species.By amino acid mutation screening,we acquired one quadruple amino acid points mutant of VirE2,which was incapable to bind Arabidopsis VIP1.After complement this mutant version VirE2 back to one AvirE2 C58 strain,it still maintained the ability of transferring T-DNA into host cells.These results might reveal that multiple bZIPs in plant might share redundant function of facilitating the A.tumefaciens mediated microbes and plant interaction.