Plant-Microbe Interactions To Improve Plant Resistance To Biotic And Abiotic Stresses

Plants live in complex environments where they interact with multiple detrimental organisms such as herbivorous insects and microbial pathogens,but also with beneficial organisms,such as carnivorous insects that reduce herbivore pressure and beneficial fungi and rhizobacteria.Beneficial microbes such as rhizobacteria and mycorrhizal fungi can help plants to 'deal' with pathogens and herbivorous insects as well as to tolerate abiotic stress.In this study,we had proved that benefical microbes could:(1)regulate the host plant growth by root exudates and bacterial secretions;(2)enhace host plant resistance to biotic and abitic stress by manipulating the composition of plant metabolits and phytohormones.Moreover,we studied the application ways of the benefical microbes in the fied and found the effects on growth promotion and disease resistance were involved in the applied manners.1.Mitsuaria sp.and Burkholderia sp.from Arabidopsis Rhizosphere Enhance Drought Tolerance in Arabidopsis and Maize(Zea mays L.)Some rhizosphere microbes,such as plant growth-promoting rhizobacteria(PGPRs),can alleviate drought stress in plants and improve crop productivity and water use efficiency under drought condition.In the present study,20 bacterial isolates from the Arabidopsis rhizosphere microbiome have been screened for their ability to improve Arabidopsis drought tolerance.Two bacterial strains,Burkholderia sp.ADR 10 and Mitsuaria sp.ADR17 had the greatest influence on drought tolerance and were further characterized.Both Burkholderia sp.ADR 10 and Mitsuaria sp.ADR 17 produced exopolysaccharides(EPS)and exhibit 1-Aminocyclopropane-l-carboxylic acid deaminase(ACCd)activity.Moreover,inoculation of both strains increased the plant survival rate,relative water content,and denfense enzyme activity of Zea mays L.plantlets subjected to drought stress which indicates both strains also alleviate the drought stress of maize under drought condition.2.Trichoderma gamsii Changed Leaf Metabolome in Arabidopsis thaliana and Affected Herbivore Feeding BehaviorPlants reprogram their transcriptome,proteome,and metabolome to fit different environments,leading improvements of capacity to deal with stress tolerance.Some studies have shown that endophyte fungus and plant growth promoting rhizobacteria(PGPR)can be positively affected plant metabolites and play an important role in inhibiting insect attack.Limited is known how rhizosphere fungus modulates the metabolites of plant and the signaling pathway it involved in.We obtained a newly isolated Trichoderma gamsii from Arabidopsis thaliana soil with capacity to inhibit feeding behavior of Trichopulsia ni larvae on Arabidopsis and studied possible mechanisms.We experimentally determined the leaf metabolome and phytohormones by GC-MS and LC-MS analysis.T.gamsii showed inhibition to larvae feeding compared with un-inoculated control plants.The application of T.gamsii altered the leaf metablome as well as phytohormones content.Arabidopsis inoculated with T.gamsii had higher amino acids,whereas un-inoculated plants had higher sugars in leaf tissues.Arabidopsis inoculated with T.gamsii had increased ABA content and decreased SA and IAA content compared to un-inoculated plants.Our study indicates that T.gamsii altered leaf metabolites and phytohormones,suggesting that fungus from soil could modulate plant leaf primary metabolites and secondary metabolites such as phytohormones.3.Root and Bacterial Secretions Regulate the Interaction between Plants and PGPR and Lead to Distinct Plant Growth Promotion EffectsPlant growth-promoting rhizobacteria(PGPR)have garnered great interest in agriculture due to their ability to influence the growth of host plants in specific ways.ABC transporters play important roles in the plant-microbe interactions through modulating plant root exudates.In the present study,we aimed at a more precise understanding of the mechanism and specificity of the interaction between PGPR and plants by using Bacillus cereus AR156 with wildtype(Col-0)and ABC transporter mutants(Atabcg30,Atabcg36,Atabcg37,Atabcc2,and Atabcc5)of Arabidopsis thaliana.The plant growth promotion effects of AR156 on Col-0 and different ABC transporter mutants were determined.The possible mechanisms of the various effects of AR156 were explored by studying the bacterial volatiles and secretions,expression level of candidate genes,and plant root exudates.We observed that AR156 promoted the shoot growth of Col-0 and Atabcg30,Atabcg36,Atabcg37 but repressed that of Atabcc5.The volatiles and secretions of AR156 promoted the shoot growth of Col-0 and Atabcg30 but had no effect on Atabcc5.We also found that root exudates of Col-0 induced the expression of AR156 genes related to siderophore and chitinase production;while root exudates of Atabcc5 inhibited the expression level of these genes.Further analysis of root exudates by Gas chromatography-mass spectrometry(GC-MS)revealed that amino acids,organic acids,and sugars were significantly less abundant in Atabcc5 when compared to the Col-0.Our findings highlight that both host plant and PGPR play active roles on the outcome of the plant-microbe interaction.4.Field Evaluation of Different Application Methods of the Mixture of Bacillus cereus strain AR156 and Bacillus subtilis strain SM21 on Pepper Growth and Disease-resistanceThe mixture of Bacillus subtilis strain SM21 andBacillus cereus strain AR156,referred to as ASB,is a biopesticide in the process of registration in China,which has the capacity of controlling root-knot nematode in cucumber,Phytophthora wilt in pepper and Ralstonia wilt in tomato.In this study,we tested its effects on a range of physiological indicators of plant growth including biomass,yield,chlorophyll content and fruit nutrients of pepper as well as its efficacy in controlling bacterial wilt caused by Ralstonia solanacearum under field conditions in 2009 and 2010 by a variety of inoculation methods.Three application methods—soaking seeds,drenching soil around seeds right after sowing and drenching the rhizosphere of transplanted seedling with the aqueous solution(as a soil drench)—and three concentrations of ASB(1.0×10~6 CFU/mL,1.0×10~7 CFU/mL,and 1.0×10~8 CFU/mL)were employed.The results showed that both soaking seeds with ASB at 1.0×10~7CFU/mL as well as drenching rhizosphere with ASB at 1.0×10~6 CFU/mL and 1.0×10~7 CFU/mL promoted growth,increased yield and fruit nutrient contents of pepper.The combination of these two inoculation methods led to significant increases in growth and fruit nutrient contents.We found that the most effective way was the combination of soaking seeds with the ASB at 1.0×10~7CFU/mL and drenching rhizosphere with it at 1.0×10~6CFU/mL,which is also easy for Chinese farmers to implement.