Interactions Between Bemisia Tabaci And Its Endosymbionts Wolbachia And Cardinium And Their Biological Effects On The Host

As a wordwide "super pest",Bemisia tabaci can not only directly feed on vegetables and flowers,but indirectly transmit plant viruses,causing huge economic losses to agricultural production.The symbiotic bacteria Wolbachia and Cardinium are widely distributed in arthropods.The use of Wolbachia-induced cytoplasmic incompatibility(CI)to control medical vector insects has been proven to be feasible,while Cardinium-induced CI effects are rarely reported.The wMel strain in Drosophila melanogaster has attracted attention due to the induction of CI and blocks the spread of dengue disease.However,it is unclear whether this strain can colonize and induce CI in distant host insect.In our study,the Wolbachia strain was artificially transferred into the distant host B.tabaci by microinjection investigating the stable inheritance and monitoring the titers of the exogenous Wolbachia in the new host.Dynamic changes and the host phenotype induced by the two commensal bacteria provided a theoretical basis for the use of Wolbachia to control B.tabaci populations.In addition,the transcriptome sequencing was used to study the molecular responses of B.tabaci to exogenous Wolbachia transfection and to explore the interaction mechanism between Wolbachia and the host.After a lot of work,a series of important research results has obtained as follows:(I)Wolbachia was isolated and purified fom Drosophila melanogaster and transferred into B.tabaci by microinjection,simultaneously a whitefly-transplanted isofemale line was constructed.Based on the molecular detection of isofemale,,the results showed that wMel strains could still be detected in the 15th generation(G15)of B.tabaci after transfection,indicating that the exogenous Wolbachia wMel strain has been successfully transferred to a new host and could be inherited stably in offsprings,but the maternal transmission rate of each generation shows a fluctuating trend,presumably this may be the result of the interaction between defense and anti-defense between B.tabaci and invasive strains.(2)FISH was used to detect and localize Wolbachia and Cardinium in B.tabaci.The results showed that the fluorescence signal was detected in different generations and at different developmental stages of B.tabaci,and the signal was strongest in bacteriocyte.Cardinium had a strong fluorescence signal in the pseudopupa,bacteriocyte and surrounding tissues and the upper part of the head.Both are distributed,and the adults are mainly distributed in the abdominal bacteria cells.(3)Using real-time fluorescence quantitative PCR to analyze the titer of wMel strains transfected with B.tabaci in different generations and different genders.The results of continuous testing for 12 generations showed that the titer of the strains between different generations showed a fluctuation pattern that decreased at first and then increased,and the titer reached the peak in the G6 generation.Overall,the titer in females was higher than that in males.The nymph titers were higher than adults.However,the linear correlation analysis showed that there was no significant correlation between the changes in titer and the dynamics of transmission efficiency.(4)Biological hybridization experiments.Through different combinations of transfected and non-transfected B.tabaci,the results showed that wMel strain could induce strong Cl in B.tabaci and had no significant effect on the acceptor host fitness.Cardinium did not induce Cl in the population of B.tabaci,further demonstrating the CI effect of exogenous Wolbachia-induced within B.tabaci.(5)Covering population control experiments.In this study,different methods were used to release transfected whitefly to investigate the feasibility of using Wolbachia to regulate the population of B.tabaci.The results showed that compared with the continuous three generations of releasing only transfected females or cross-combining release of transfected females or males,only males infected with the males resulted in 73.3%of male offspring,which could severely distort the sex ratio of the target population.This provides valuable evidence for using the wMel strains to control B.tabaci population.(6)Transcriptomic sequencing was performed on B.tabaci by transfected after 24h and the wild population.Data analysis showed that there are 1579 Unigene induced differential expression post transfection.GO and KEGG pathway enrichment analysis showed that wMel transfection significantly activated basal metabolic pathways,humoral and cellular immune pathways,and stress pathways.This study lays a solid foundation for further in-depth understanding of the interaction between Wolbachia and host insects.In conclusion,this research successfully transfected exogenous Wolbachia into B.tabaci,and monitored the transmission dynamics of wMel strains in offspring populations for a longer period of time.On this basis,a bio-hybridization experiment was conducted to prove that wMel strain can induce strong CI in B.tabaci.Based on this,this paper carried out experiments on population control of B.tabaci,and showed a good application prospect.Finally,the authors performed transcriptome sequencing and data analysis on the transfected single female line and found a large number of valuable candidate genes,laying a solid foundation for further verification of candidate gene function and in-depth study of Wolbachia-host interactions,and also provides an important scientific basis for the use of Wolbachia for the regulation of important agricultural pest populations.