| Wolbachia are maternally inherited intracellular bacteria of a wide range of arthropods and filarial nematode, capable of spreading through populations by reproductive manipulation such as cytoplasmic incompatibility (CI), parthenogenesis inducing, feminization and male killing. In addition, Wolbachia can also affect their hosts’ fitness including fertility, longevity, female ratio and development time. Currently, Wolbachia has been one of the most striking leading edge due to its roles on manipulating the hosts’ reproduction. The most common phenotype is CI, but the molecular mechanisms are still unknown. Studies on CI show that sperm is modified by Wolbachia during spermatogenesis and this modification prevents the paternal chromosomes from entering the anaphase of the first division leading to a defect in embryogenesis. Some other studies show that Wolbachia could interfere with the gene expression level of the host which results in the different phenotypes. The molecular mechanism between Wolbachia and its hosts is striking and the researchers have been engaged in solving this problem. Tetranychus urticae Koch belongs to Arachnida, Acari, Acariformes, Tetranychidae, Tetranychus. T. urticae, which infected with Wolbachia naturally, is a very important mite pest. Our results help to comprehend the relationship between Wolbachia and the two-spotted spider mite preliminarily and it will be helpful to use Wolbachia as a biocontrol approach to control the mite pest. This will be significant in agricultural production.Two populations of T. urticae, the Fujian (FJ) and Huhhot (HU), were used in this study to understand the effect of Wolbachia on the reproduction and fitness of the two-spotted spider mite in China. The reproduction and fitness of Fujian population (FJ) were compared with the result performed on Huhhot population (HU) before. The transcriptome of Huhhot (HU) was sequenced and qRT-PCR validation was performed in the two populations. Our study showed that the effect of Wolbachia on the reproduction and fitness of the T. urticae host was essentially dependent on the host genetic background. It also revealed that the different gene expression in the host induced by Wolbachia led to the abnormal special biological phenotypes. This provided a theoretical basis for us to understand the molecular mechanism between Wolbachia and the hosts deeply.We got two strains of T. urticae collected from Fujian (FJ) respectively:one was naturally infected with Wolbachia and the other one was naturally uninfected. The hybridization experiments showed that Wolbachia induced intermediate CI. This result was different with the data of Huhhot population (HU) in which Wolbachia induced strong CI. Then we sequenced wsp gene of Wolbachia, the COI gene and ITS section of the two populations. We found the sequences of Wolbachia wsp genes were identical. The ITS sections were of the same sequence but the sequences of COI genes were different. This suggested Wolbachia strain was identical in two populations while the genetic backgrounds of the two hosts were different. This study defined that Wolbachia could regulate the reproduction of the Fujian population (FJ) of T. urticae. In addition, the degree of CI might be modified by the host genetic background.We measured the potential effect of Wolbachia on infected and uninfected strains in the Fujian population (FJ) of T. urticae by using the methods established before. The results showed Wolbachia could improve the hatch rate of eggs and the female ratio while could extend the development time of the offsprings. There was no effect on fecundity and host longevity. There were also many differences with the results of Huhhot population (HU). Furthermore, this comparison also confirmed that the host genetic background played an important role in the interactions of the symbiont. The interaction in different symbionts might be different.On the base of the results of biological experiments, the transcriptome of Huhhot population (HU) was sequenced. We expected to get more genetic information and tried to give some fundamental explanations of the molecular mechanisms of the interaction between Wolbachia and their hosts. Comparison of gene expression profiles revealed significant differences in the presence of Wolbachia. Expression profiles for a few genes were confirmed by Quantitative Reverse Transcriptase PCR (qRT-PCR) in Huhhot population (HU) and the results were almost consistent with the profiles. Based on the Gene Ontology (GO) and KEGG Pathway, a large number of genes were enriched in redox and metabolic biological processes (BP). In addition, many significantly expressed genes were enriched for putative protein and their functions were unclear. To our surprise, no gene related to reproduction and immune was enriched. We know that the genome information is not perfect now and new data had been submitted. This might be a reason for the imperfection of gene functional annotation. From these significantly expressed genes, we chose some genes related to redox and metabolic, and some potential genes related to reproduction and immune processes to study the potential molecular mechanisms in reproduction and fitness regulations of T. urticae induced by Wolbachia. For another reason, we performed qRT-PCR to quantify the gene expression in Fujian population (FJ) of T. urticae. And a large number of genes also showed different expression levels in infected and uninfected hosts. But the expression manner was different with the profile in Huhhot population (HU). This difference might also be the contribution of the host genetic background, the interaction and co-evolution of the symbiont. But the main genes had the same expression behaviour in the two populations, so we presumed Wolbachia might use the same molecular mechanism to manipulate the reproduction and fitness in T. urticae populations. These results provided a favorable theoretical foundation for further deeply exploring the molecular mechanisms of the interaction between Wolbachia and its two-spotted spider mite or other insect hosts’ reproduction and fitness. |
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