Tripartite Associations Among Bacteriophage WO, Wolbachia, and Host Affected in the Two-Spotted Spider Mite Tetranychus Urticae Koch
|School||Nanjing Agricultural College|
|Course||Agricultural Entomology and Pest Control|
|Keywords||Two-spotted spider mite (red form) Wolbachia WO Temperature Age Cardinium|
Wolbachia are maternally inherited obligatory intracellular symbionts that infect a wide range of arthropods, and can induce various reproductive disorders, such as cytoplasmic incompatibility (CI), thelytokous parthenogenesis, feminization and male killing. CI is the most common reproductive disorder, the phenotype of which is usually expressed as reduced hatchability or strongly male-biased sex ratios when uninfected females cross with infected males (unidirectional CI) or infected females cross with males infected different Wolbachia strains (bidirectional CI). When the mechanisms involved in the effect of CI are studied, an extraordinary high level of mobile elements in the genome of Wolbachia is discovered. Many studies have proved that there are bacteriophages in Wolbachia, which named WO, and proposed as a potential tool for genetically modifying mosquito vectors.The absence of relation between phage phylogeny based on orf7 sequences and the effects induced by Wolbachia suggests that WO is not directly involved in these effects. Furthermore, several studies have demonstrated a negative correlation between WO density and Wolbachia density, and a positive correlation between Wolbachia density and CI. Based on these, the Phage Density Model is proposed. However, this model is not universal. The hypothesis that has been posed is that WO might alternate lytic and lysogenic life cycles or change phage production under certain conditions including temperature, insect age and host species background and other intracellular symbionts in the same host.In this study,20 isolated geographic populations of the two-spotted spider mite were collected, and the diversity and evolutionary dynamics of WO-Wolbachia associations was studied. To better understand the tripartite associations among WO, Wolbachia and host, different temperature and different insect age were set, and another intracellular symbiont Cardinium in the same host was used.1. All of the 20 isolated geographic populations of the two-spotted spider mite were infected with Wolbachia, and only six geographic populations were found carrying WO. There were four different Wolbachia strains that carrying WO, and belonged to two subgroups of B-Wolbachia, Con and Ori. Sequences of WO in six geographic populations can be divided into two types:WOwUrtl (HM623911) and WOwUrt2 (HM623912), which had 16 bases of difference. No phylogenetic congruence was found between WO and Wolbachia in our study. Besides, divergent Wolbachia strains that co-infect same host shared identical phage. Based on these, WO may transfer horizontally between Wolbachia endosymbionts in the two-spotted spider mite. In addition, based on phylogenetic analysis, WO in Wolbachia that infected the two-spotted spider mite was confirmed to belong to group II, which was the foundation for further study.2. To better understand the tripartite associations among WO, Wolbachia and host, the experiment was carried out at the following temperatures:19℃,22℃,25℃,28℃and 31℃. The ZJ and YC geographic populations, which were infected with two different Wolbachia but carried the same WO type (WOwUrtl), were studied. The result showed that WO might alternate from lysogenic to lytic cycles at extreme high or low temperatures, and changed the tripartite associations.3. To better understand the effect of male age on the abundance of WO and Wolbachia, 8 divergent male ages were used. In our study, the abundance of WO increased with age, while the abundance of Wolbachia first increased with age, then keep invariant, and at last decreased when WO changed to the lytic cycle (1.4×105 copy number, different value in different hosts).4. The abundance of WO and Wolbachia were studied on the effect of another intracellular symbiont Cardinium by Realtime quantitative PCR. Two lines of ZJ population (Wolbachia-Cardinium double-infected line W+C+and Wolbachia single-infected line W+C－) were used as the subjects. The result showed that the effect of Cardinium on the abundance of WO and Wolbachia may be impacted by sex. Cardinium promoted both Wolbachia and WO increasing in female mites, while Cardinium restrained Wolbachia by promoting the WO increasing in male mites.