Evolution of Wolbachia reproductive and nutritional mutualism: insights from the genomes of two novel strains that double infect the pollinator of dioecious Ficus hirta.

Abstract

Wolbachia is a genus of maternally inherited endosymbionts that can affect reproduction of their hosts and influence metabolic processes. The pollinator, Valisia javana, is common in the male syconium of the dioecious fig Ficus hirta. Based on a high-quality chromosome-level V. javana genome with PacBio long-read and Illumina short-read sequencing, we discovered a sizeable proportion of Wolbachia sequences and used these to assemble two novel Wolbachia strains belonging to supergroup A. We explored its phylogenetic relationship with described Wolbachia strains based on MLST sequences and the possibility of induction of CI (cytoplasmic incompatibility) in this strain by examining the presence of cif genes known to be responsible for CI in other insects. We also identified mobile genetic elements including prophages and insertion sequences, genes related to biotin synthesis and metabolism. A total of two prophages and 256 insertion sequences were found. The prophage WOjav1 is cryptic (structure incomplete) and WOjav2 is relatively intact. IS5 is the dominant transposon family. At least three pairs of type I cif genes with three copies were found which may cause strong CI although this needs experimental verification; we also considered possible nutritional effects of the Wolbachia by identifying genes related to biotin production, absorption and metabolism. This study provides a resource for further studies of Wolbachia-pollinator-host plant interactions.