| Arthropods are frequently associated with multiple endosymbionts.In the insect-symbiont-plant tripartite interaction systems,insect symbionts have been showed to be an important role in insect-plant interactions.The interaction among insect,endosymbiont and plant are explored to clarify the mechanism of outbreaks of insect populations and the incidence of symbiotic bacteria,as well as the co-evolution process of plant-endosymbiont-insect.The spider mite,Tetranychus truncatus Ehara,is an impotant pest that feeds on many agricultural crops causing extensive damage leading to crop and productivity loss.In recent years,there were devastating outbreaks of T.truncatus in China.The spider mite has become the dominant species on many crops.The spider mite' harbored a wide variety of endosymbiotic bacteria and these endosymbionts significantly improved their host fitness,which is potentially an important factor in the outbreaks of the host.However,the incidence of endosymbiont distribution and the infection patterns in spider mite are mostly poorly understood.The change of bacterial diversity and community composition of spider mites under different environmental factors remains unclear.The mechanisms underlying the symbiont-mediated interaction between spider mite and host plants are still unclear.Considering that the correlation involving resource and space between spider mite,symbiont and plant,and the potential role of symbiorits in outbreaks of mites,a complete and systematic studies,from the perspective of mite-symbionts-plant interaction,involved in the changes of the bacterial community of spider mite influence the interaction between host and plant should be performed.In this study,we firstly examined the occurrence patterns of the endosymbiont in natural populations of the spider mite and investigated the association between endosymbionts prevalence and environmental factors.Secondly,we characterized the bacterial diversity and community composition of spider mites,especially the change of the abundance of endosymbionts,under different conditions in the laboratory.To explore the role of endosymbionts in host fitness.Finally,we investigated the influence of the endosymbionts of spider mite on plant defense and amino acid metabolism,and identified the components of saliva in endosymbiont infected and uninfected mites,which will reveal the mechanism of symbionts-mediated interactions between mite and host plant.The results are summarized as follows:I.Incidence of facultative bacterial endosymbionts in the natural population of spider mites associated with local environments and host plantsWe surveyed endosymbionts in natural populations of the spider mite,T.truncatus,in China,screening 935 spider mites from 21 localities and 12 host plant species.Three facultative endosymbiont lineages,Wolbachia,Cardinium,and Spiroplasma,were detected.The infection frequencies of those three endosymbionts were variable among different sampling locations.Endosymbiont infection frequencies exhibited associations with environmental factors.The frequencies of Wolbachia,Cardinium,and Spiroplasma may be driven by factors associated both with geography(i.e.,latitude,longitude,and altitude)and with climate(i.e.,annual mean temperature and annual precipitation).Geographical factors have a dominant effect on the frequencies of the endosymbionts in spider mites.Host plants exhibited significant effects on the infection frequencies of Wolbachia.Multiple endosymbiont infections were observed and co-infections of unrelated endosymbionts in spider mite individuals were significantly higher than expected across populations.II.A change in the bacterial community of spider mites decreases fecundity on multiple host plantsBy using a high-throughput 16S rRNA amplicon sequencing approach,we characterized the bacterial diversity and community composition of spider mites fed on five host plants after communities were modified following tetracycline exposure.Bacterial diversity tended to decrease after antibiotic exposure but was also influenced by host plant type.In particular,abundance of the maternally inherited endosymbionts Wolbachia and Spiroplasma was reduced following antibiotic exposure although the reduction differed among host plants.Across all host plants,there was a tendency for daily fecundity to be lower in the mites with reduced bacterial diversity following the antibiotic treatment.Our data suggest that host plants and antibiotics can shape spider mite bacterial communities and that bacterial symbionts improve mite performance.III.Temperature influence spider mite bacterial communities that mediate host fecundityBy using a high-throughput 16S rRNA amplicon sequencing approach,we examined the effect of different developmental temperature(20,25,30 and 35?)on the microbial community and fecundity of spider mites.The bacterial diversity and community composition of spider mites were influenced by temperature.Particularly,abundance of the endosymbionts Wolbachia was also influenced by temperature.The spider mite reared at low temperature(20?)for one generations,the endosymbiont Wolbachia was not detected.Across all temperature,daily fecundity tended to be lower after the antibiotic treatment.?.Influence of spider mite microbial symbionts on plant defense and amino acid metabolism:consequences for spider mite fitnessHerbivorous spider mites possess different species of bacterial symbionts that alter the interaction of plants and mites.We tested to which extent mites with and without symbiotic bacteria induce plant defences in terms of phytohormone accumulation and defence gene expression,and assessed mite oviposition and survival as a measure for plant resistance.The facultative symbionts Wolbachia and Spiroplasma co-infected spider mite T.truncates can significantly enhance the reproductive performance of mites on tomato.We also observed that the absence of these bacteria altered distinct plant defence parameters,such as defense enzyme activity and JA/SA-marker gene expression,but no effect on phytohormone accumulation,suggesting that spider mites alter tomato induce defenses downstream of the JA and SA biosynthesis pathway and independently from hormonal crosstalk.These results indicate that bacterial endosymbionts of spider mites can modulate the plant's defense response to mites.In addition,the presence of endosymbionts in spider mites can decreased the accumulation of tomato free amino acid.The data revealed that spider mite-associated bacterial symbionts can change the plant defense and amino acid metabolism that enhance the mite performance.?.Comparative analyses of salivary proteins from the facultative symbionts-infected and uninfected spider mitesSalivary constituents of spider mites have been proposed to play an important role in manipulating the outcome of plant-mite interactions.By using shotgun LC-MS/MS analysis,we identified and characterized the components of saliva in Wolbachia-Spiroplasma infected and uninfected spider mite T.truncatus.In total,177 putative salivary proteins were identified,among those proteins,14 proteins were only found in Wolbachia-Spiroplasma infected spider mite.The saliva enzymes included oxidoreductase,hydratase,isomerase,transferase,protease,esterase,ribonuclease,kinase,lyase and phosphorylase.Other proteins,such as ATP-binding,actin,heat shock proteins and vitellogenin were also detected in the T.truncatus saliva.The function of many proteins are unknown,while in numerous cases belong to catalytic activity and binding proteins.Endosymbionts infection in spider mite alters the host saliva protein is likely as a key factors in manipulating the outcome of plant-insect interactions.In summary,we investigated the incidence of facultative bacterial endosymbionts in the natural population of spider mites.Combined with the laboratory and field studies,we explored the influences of different environmental factors(i.e.,host plant species and temperature)on spider mites bacterial community and fecundity.We also clarified the mechanism of endosymbiots-mediated interaction between T.truncatus and host plants.The present study contributes to clarify the interaction between plant-endosymbiont-insect,and that could be useful in controlling of mite pests and ensure the safety of agricultural production. |
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