| Rhizosphere microbiota are closely related to plants.Among them,arbuscular mycorrhizal fungi(AMF)that can symbiose with plants and rhizobacteria are two important groups.In the rhizosphere zone,AMF and rhizobacteria often exist together.However,most of the researches about plant-microbe interaction only focuse on the relationship between plant-AMF or plant-rhizobacteria,ignoring the interaction among host plants,AMF and rhizobacterial community.In order to deep our understanding of plant-microbe interaction,we started from the important crops: wheat(Triticum aestivum)and rice(Oryza sativa),explored structure and function of rhizobacteria communities of these two crops that inoculated AMF.To be specific,we targeted on these questions:(1)How does AMF influence rhizobacterial community composition and diversity?(2)How does the rhizobacterial community at plants that inoculated AMF respond to pathogen,and what kind of function does bacteria perform? We drew conclusions as following:1.AMF influenced the structure and diversity of rhizosphere microbial communityWe collected rhizosphere soil of rice and wheat inoculated AMF(Glomus tortuosum)or not,extracted DNA from which and used 16 S r RNA sequencing technology to analyze the structure and diversity of rhizobacterial communities.Results showed that in the rhizosphere of rice inoculated AMF,abundance of Alphaproteobacteria was highest,in the rhizosphere of wheat inoculated AMF,class with highest abundance was Gammaproteobacteria.In addition,AMF changed βdiversity of rhizobacterial community.These indicated that AMF can influence the structure and diversity of rhizobacterial community significantly.Moreover,we found that rhizobacterial community of rice inoculated with AMF shifted at different development stage.Abundance of Bacillaceae decreased along the rice growth,while the abundance of Sphingomonadaceae increased.We noticed that abundance of some bacteria showed opposite trends in the rice and wheat after inoculating AMF: the relative abundance of Alphaproteobacteria in the rhizosphere of rice decreased by 50%,while the relative abundance of this class in wheat increased by 2 times;the relative abundance of Gammaproteobacteria in the rhizosphere of rice didn’t show significantly change,while the abundance of this class in the rhizosphere of wheat increased 2 times.These two classes include a variety of plant growth-promoting rhizobacteria(PGPR)such as Rhizobiaceae and Pseudomonadaceae,which may play important roles in the process of plant growth.Further,we set up treatment that inoculated Acaulospora scrobiculata,Glomus tortuosum,Gigaspora margarita,mixed AMF,bacteria within AMF inoculant respectively and control group without AMF inoculation on wheat and performed 16 S r RNA sequencing on rhizobacterial communities for each treatment.Results showed that β diversity of control and treatment that inoculated bacteria within AMF inoculant was similar,but rhizobacterial community changed after inoculating wheat with AMF:Pseudomonas dominated the wheat rhizosphere microbial community after AMF inoculation,and the abundance of this genus increased 3 times compared with the control group.In conclusion,it is AMF rather than bacteria within AMF inoculant that changed rhizobacterial community,and AMF increased abundance of bacteria that can improve plant fitness such as Pseudomonas.2.AMF helped plants reduce the negative impacts of pathogen by regulating the composition of the rhizobacterial communityWe set up pathogen(Fusarium oxysporum)treatment and non-pathogen treatment for the wheat didn’t inoculated AMF and wheat inoculated with different AMF,then verified the protective ability of AMF on plants by examining the changes of plant biomass and analyzed rhizosphere microbial community structure and diversity shift by16 S r RNA sequencing.In addition,we picked bacteria that could antagonize pathogen from the rhizosphere of wheat inoculated with both AMF and pathogen,then tested the ability of bacteria to protect plants by comparing the biomass changes of wheat and treatment inoculated with antagonistic bacterial community when facing pathogen.Our results illustrated that AMF could help plant reduce negative influence caused by F.oxysporum,and we noticed that AMF treatment changed rhizobacterial community composition after inoculating plant with pathogen.To be specific,abundance of Pseudomonadaceae and Burkholderiaceae in the rhizosphere increased to about 2 times at AMF treatment after inoculating plants with pathogen.Then,we isolated and identified the bacteria in the rhizosphere,and picked two strains with the function of inhibiting pathogen growth and spore germination(Pseudomonas soli strain F-279 and Beijerinckia fluminensis)from 220 strains isolated from rhizoshpere.Results showed community composed by Pseudomonas soli strain F-279 and Beijerinckia fluminensis were able to release the stress of pathogen on plants.Collectively,rhizobacteria played an important role in disease resistance process: AMF help plant antagonize pathogen by the way of enriching biocontrol bacteria such as Pseudomonas.Taken together,our experiments explored the rhizobacterial community that is often neglected in AMF studies,anchored bacteria that may respond to AMF,highlighted the important role of crop rhizobacterial community in the process of antagonize pathogen,and laid a good foundation for further study about interaction of microbe in the rhizosphere. |
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