| Root-knot nematode has been regcognized as one of the most important crop pests and main limiting factors for sustainable crop production.The studies have recently demonstrated a great correlation between the occurrence and development of phytopathogenisis and the plant-associated microbiome.Therefore,understanding of rhizobacterial and endophytic community composition,structure,succession and diversity in the root-knot nematode-infected plant,their shaoping mechanism ans their interaction with host and nematode pest will be a great theoretical and scientific significance to develop new biocontrol resources and biological control strategies for the plant-parasitic nematodes.In this study,to reveal the bacteria associated with root-knot nematode infestation,the community structure and diversity of rhizosphere and endophytic bacteria in different plants infected by root-knot nematodes was first investigated by using high-throughput sequencing technology.The results showed that there as a similar community structure of endophytes in different plants infected by root-knot nematode.And also,there was no significant difference in bacterial diversity.Nematode infestation had an significant effect on the species abundance of endophytic bacteria.For example,Burkholderiales,Sphingobacteriales,and Pseudomonadales were more abundant in infected nematode samples than healthy plant samples.In the nematode-infected plants,there was a similar microbial structure and abundance of endophytes between root knots and non-root-knot roots,but with a higher abundance of the dominant species Sphingobacteriales in root knots.The Beta diversity analysis showed that the plant species had a predominant influence on microbial structure and diversity of plant endophytic and rhizobacterial communities,while nematode infestation had an effect on species abundance in both root knots and non-root-knot root microbiome.No obvious separation tendency was observed between diseased plant samples and healthy samples in the cluster analysis.Community structure and diversity of endophytic and rhizospheric bacterial populations at different stages of the tomato root-knot nematode infestation was further investigated.The dominant flora of non-knot roots(TR)included Rhizobiales,Burkholderiales,Streptomycetales,Micrococcales and Bacillales etc,while the dominant population of the root-knot(TRK)endophytes are mainly composed of Rhizobiales,Burkholderiales,Streptomycetales,Micrococcales,Enterobacteriales etc.The microbial diversity of soil samples was significantly higher than those of root knots and non-kont root samples,while there was no significant difference between root knots and non-kont samples.The dominant bacterial populations of root endophytes were significantly different at different stages of the nematode-infected tomato samples,indicating that nematode infestation had a significant effect on the community composition and bacterial diversity of tomato endophyte microbiome.Beta diversity analysis showed a similar commmunity coposition of rhizobacteria and a significantly different endophytic bacteria at different stages of the nematode-infected tomato root.Functional analysis for microbiome associated the tomato root knots(IRG),non-knot root(IRH)and rhizosphere soil was performed through metagenome sequencing based the previous knowledge on community composition and bacterial diversity of the nematode-infected tomato-associated microbiome.In the 77.63%.40.07%,and 31.07%of the known functional proteins,with a high proportion of functional proteins related to metabolim,were annotated in the three metagenomic samples IRG,IHR and IRS,respectively.The analysis results showed the invovlement of plant microorganisms in the metabolism of carbohydrates,proteins,coenzymes,and vitamins.Further functional analysis demonstrated that the enzymes involved in cell wall degradation were identified in the three metagenomic samples IRG,IHR and IRS,with the largest number of enzyme genes in root knots microbiome,followed by the rhizosphere soil bacteria.The result provide the clues to for the understanding of the process of nematode infestation on plants,for example the endophytic bacteria may secrete cellulase to help the formation of root knots—the infective structure caused by nematode.In addition,abundant functional genes associated with nitrogen metabolism,have complete and 2-3 incomplete pathways of indole-acetic acid(IAA)biosynthesis in KEEG metabolic pathway analysis. |
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