Genome and Metagenome of The Phytophagous Gall-Inducing Mite Fragariocoptes Setiger (Eriophyoidea): Are Symbiotic Bacteria Responsible For Gall-Formation?

Abstract

Eriophyoid mites represent a hyperdiverse, phytophagous lineage with an unclear phylogenetic position. These mites have succeeded in colonizing nearly every seed plant species, and this evolutionary success was in part due to the mites' ability to induce galls in plants. A gall is a unique niche that provides the inducer of this modification with vital resources. The exact mechanism of gall formation is still not understood, even as to whether it is endogenic (mites directly cause galls) or exogenic (symbiotic microorganisms are involved). Here we (i) investigate the phylogenetic affinities of eriophyoids and (ii) use comparative metagenomics to test the hypothesis that the endosymbionts of eriophyoid mites are involved in gall-formation. Our phylogenomic analysis robustly inferred eriophyoids as closely related to Nematalycidae, a group of deep-soil mites belonging to Endeostigmata. Our comparative metagenomics, fluorescence in situ hybridization, and electron microscopy experiments identified two candidate endosymbiotic bacteria shared across samples, however, it is unlikely that they are gall-inducers (morphotype1: novel Wolbachia, morphotype2: possibly Agrobacterium tumefaciens). We also detected an array of plant pathogens associated with galls that may be vectored by the mites; a mite pathogenic virus (Betabaculovirus) has the potential to be used in the biocontrol of agricultural pests.