| Wolbachia are intracellular bacteria that widely infect among arthropods. Previous studies have revealed that Wolbachia have a wide range of arthropods host and are genetically diverse. To date, eleven groups (A-K) of Wolbachia strains were detected in estimated 40% of terrestrial arthropods. Wolbachia are maternally inherited through the cytoplasm, and form a stable symbiotic relationship with their hosts. However, several independent lines of evidence clearly indicate Wolbachia are also horizontally transmitted both within and among different host species. In addition, Wolbachia infection dynamics are also affected by many external conditions. Wolbachia can manipulate host reproduction and influence host fitness, immunity and other physiological function in diverse ways. As a result, Wolbachia have theoretical and practical significances in arthropod evolution, pest and human diseases control.Spider mites are cosmopolitan agricultural pests with an extensive host plant range and strong pesticide resistance, which are recognized as the most difficult control pests. Wolbachia infect various species of spider mites and have complex effects on host biology. Using symbiotic bacteria to carry out spider mites control provides us a new insight. Thus, we will unravel Wolbachia infection characters and its influences in the spider mites, and further applying Wolbachia in spider mites control.Wolbachia-associated complex biological effects on spider mites are strain specific. In this study, we first used PCR technique to examine the infection statuses of six spider mites species (Tetranychua truncatus, T. phaselus, T. pueraricola, T. urticae, T. kanzawai and Amphitetranychus viennensis), which often cause serious damge in China. Then, the sequences and recombination of wsp gene were analyzed. Results indicate that there was a high level of Wolbachia diversity in spider mites, for instance, two divergent strains were observed in T. truncatus. Distinctive strain was only found in corresponding spider mites, suggesting the potential codivergence of Wolbachia strains with their hosts. The event that T. truncatus and T. urticae were infected with an identical Wolbachia strain might be caused by horizontal transmission. Recombination events of wsp genes were also discovered.Because single gene wsp has a high recombination rate, thus the results of phylogenetic analyses based on wsp may not accurately reflect the true evolutionary and demographic histories of Wolbachia isolates. Here, we used Multilocus Sequence Typing (MLST) to confirm Wolbachia infection status, and examined the relationship between Wolbachia infection status and host phylogeny, mitochondrial diversity and geographical range in five Tetranychus species (T. truncatus, T. urticae, T. pueraricola, T. phaselus and T. kanzawai) from 21 populations in China. The prevalence of Wolbachia within the five Tetranychus species ranged from 31.4% to 100%and the strains were remarkably diverse. Together, these observations indicate that Wolbachia was introduced to these populations on multiple separate occasions. As in other arthropods, the same Tetranychus species can accommodate very different strains, and identical Wolbachia occasionally infect different species. These observations suggest that Wolbachia are transmitted both vertically and horizontally. Horizontally transmission is probably mediated by the host plants. The distribution patterns of Wolbachia were quite different among populations of the same species, suggesting that the dynamics of Wolbachia in nature may be affected by ecological and other factors.Hawthorn spider mite(Amphitetranychus viennensis), one of the most important pest mites on fruit trees, often causes serious damage to agricultural industry. However, little is known about the characteristic and reproductive effects of Wolbachia infection in A. viennensis. The Wolbachia infection of natural population spider mite was analyzed using MLST. By crossing and biological experiments, the effects of Wolbachia on host reproduction were observed. Results indicated that A. viennensis infected with a Wolbachia strain, wVie, which has a closer phylogenetic relationship with Wolbachia from Orius strigicollis and Nasonia vitripennis than with Wolbachia from other spider mite of Tetranychus genus. Wolbachia are associated with four little divergence mitochondrial haplotypes, suggesting a recent Wolbachia infection. No effect of Wolbachia on A. viennensis fecundity was detected. Wolbachia induced weak CI in A. viennensis, showing that infected male mated with uninfected female, egg hatching rate was significantly lower, while offspring sex ratio and mortality did not change significantly.By comparing the relationship between Wolbachia infection types and spider mites mitochondrial haplotypes, we explored the influences of Wolbachia on spider mites mitochondrial diversity and evolution. In seven natural populations of Tetranychus truncatus in current study, five Wolbachia strains (wtrul, wtru5, wtru7, wtru8 and wtrul2) were detected, suggesting that multiple separate introductions have occurred. Part of mitochondrial COI gene was sequenced from infected individuals revealing ten different haplotypes. As predicted, the haplotype and nucleotide diversity were lower in infected individuals than in uninfected individuals. Furthermore, phylogenetic and AMOVA analyses revealed that the distribution of mtDNA haplotypes is not associated with geography. Rather, it is strongly concordant with infection status. This data supports the hypothesis that Wolbachia infection can affect the genetic structure and diversity of the host.In spider mites, multiple studies have concluded that Wolbachia can induce complex cytoplasmic incompatibility (CI) phenotypes and fitness changes. However, little is known about the molecular mechanisms underlying these phenotypic effects. In this study, we selected a strain of T. urticae, in which Wolbachia infection was associated with strong CI and enhanced female fecundity, to investigate the transcriptional responses of T. urticae to Wolbachia infection through transcriptome analyses. After sequencing and mapping to reference genome, sufficient transcriptome data for downstream analyses were obtained. Results indicated that the T. urticae transcriptional patterns are sex-specific. A subset of genes showed differential expression in response to Wolbachia infection in female and male respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of differentially expressed genes revealed that many metabolic pathways were affected by Wolbachia infection. The expressions of genes related to oxidation-reduction process, digestion and detoxification, lipocalins and unknown function were profoundly influenced. In addition, several regulated genes with potential roles in reproduction were detected. Interestingly, unlike other studied Wolbachia-host associations, no clear evidence of host immune priming by Wolbachia was found, although a few potential immune genes were affected. This study provided us a new insight for understanding of the complex interactions between arthropods and Wolbachia. |
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