Effects Of Host Interaction With Wolbachia On Cytoplasmic Incompatibility In The Two-spotted Spider Mite Tetranychus Urticae

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(Cl),parthenogenesis inducing,feminization and male killing.The most common phenotype is Cl,but the molecular mechanisms are still unknown.Tetranychus urticae Koch belongs to Arachnida.Acari,Acariformes,Tetranychidae,Tetranychus.T.urticae,which infected with Wolbachia naturally,is a very important mite pest.It will be helpful to use Wolbachia as a biocontrol approach to control the mite pest.Ankyrin repeat(ANK),which is a ubiquitous structural motif consisting of about 33 residues,has been identified in a large number of proteins.ANK proteins can mediate protein-protein interactions,studies have suggested that ANK genes may be implicated in the molecular basis of CI.Three populations of T.urticae,the Yunnan(YN),Huhbot(HU)and Fujian(FJ),were used in this study to understand the effect of Wolbachia on the reproduction of the two-spotted spider mite in China.The hybridization experiments showed that Wolbachia induced strong Cl in YN,intermediate Cl in HU,weak Cl in FJ.This moderate to strong Cl was also found in inter-population crosses including two introgression results:being weak in crosses involving FJ nuclear background males and strong in those with YN nuclear background males.Then we sequenced wsp gene and a set of housekeeping genes of Wolbachia,the COI gene and ITS section of three populations.We found the sequences of Wolbachia wsp genes and a set of housekeeping genes were identical among three populations.The ITS sections were of the same sequence but the sequences of COI genes were different.This suggested Wolbachia strain was identical in three populations while the genetic backgrounds of the hosts were different.This study showed that Wolbachia could regulate the reproduction of T.urticae.In addition,the degree of CI might be modified by the host genetic background.Moreover,relative density of Wolbachia in male mites and effect of male age were also analyzed.Our results suggested that male age,Wolbachia density are not factors determining intensity of Cl in T.urticae.To understand the relationship between ANK genes and Cl,we identified ANK homologues in three different T.urticae populations with the wMel Wolbachia strain,which causes Cl in Drosophila.Quantification of ANK gene expression was also carried out in adults over time to understand its expression dynamics in Wolbachia-infected T.urticae.Quantitative analysis and comparison of ANK homologues expression in male adult T.urticae indicated they were correlated with Cl expression.Our results describe a new interaction between Wolbachia and their hosts,the effect of this interaction on Cl,and provided evidence that the interaction of host and ANK genes might be a critical step in the molecular mechanism of CIL In addition,further investigation on the functions of Wolbachia ankyrin gene products,particularly with respect to host reproductive manipulation,is also imperative.