Isolation And Identification Of Insertion Sequences In The Symbiont Wolbachia Of Rice Water Weevil

The rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel (Coleoptera, Curculionidae) is an alien insect species in China which invaded this country in late 1980s. This weevil reproduces mainly through amphigenesis and concurrently reproduces parthenogenetically in native regions, but only parthenogenesis occurs in all of invaded regions. Attainment of parthenogenesis is considered as a key factor favoring its successful invasion and rapid dispersion of RWW. Wolbachia is well-known important symbiotic bacterium which distributes widely in arthropods and parasitoid nematodes. This bacterium plays several important modulating roles on the reproduction of hosts, which leads to feminization of male chromosome, parthenogenesis, lethality to male, and cytoplasmic incompatibility. Wolbachia has been reported existing in the reproductive system RWW. This study focused on isolation and identification of insertion sequences from the genomes of Wolbachia in RWW, aiming at providing a basis for further studies regarding possible mechanisms of Wolbachia inducing parthenogenesis in this weevil.Two IS3 sequences, two IS4 sequences and four IS5 sequences were cloned and identified from the genomes of Wolbachia in different geographic populations of RWW. The two IS3 sequences, IS3-1278 and IS3-1275, have a homogeneity of 75.4% and they share 78% and 79% of homogeneity, respectively, with the IS3 sequences from Drosophila. But the coded amino acids sequences of these two IS3 fragments have only 40% of similarity when blasted with amino acids sequences from the GeneBank DataBase.There is only 30.4% of homogeneity between the two IS4 sequences, IS4-1433 and IS4-880. A high homogeneity (86%) existed between the IS4-1433 and the IS4 sequences from Drosophila, but the IS4-880 has no high homogeneity with any of IS4 sequences in GeneBank DataBase. There is a high homogeneity (85%) between the coded amino acid sequence of IS4-1433 gene and that of IS4 family of Drosophila. Just one IS5 sequence from RWW, IS5-740, has homogeneity of around 50% when comparing the coded amino acid sequence with those from Drosophila.The results implied that the weevils in invaded regions might have been infected by different species of Wolbachia from those in native regions, and some populations be infected by two species of Wolbachia, as indicated by the great different in IS3 and IS4 sequences existing among weevil populations. We speculated that, in order to avoid population decline possibly induced by parthenogenesis-associated gene degeneration, populations of this weevil in invasive regions needed somehow new genes to be transformed into their genomes. As an important symbiotic bacterium in the reproductive system of the weevil, Wolbachia might serve as a transforming vector, which, subsequently, would exert some effects on the reproduction mechanism of this weevil.