title: Type III secretion systems and the evolution of mutualistic endosymbiosis.
abstract: The view that parasites can develop cooperative symbiotic relationships with their hosts is both appealing and widely held; however, there is no molecular genetic evidence of such a transition. Here we demonstrate that a mutualistic bacterial endosymbiont of grain weevils maintains and expresses inv/spa genes encoding a type III secretion system homologous to that used for invasion by bacterial pathogens. Phylogenetic analyses indicate that inv/spa genes were present in presymbiotic ancestors of the weevil endosymbionts, occurring at least 50 million years ago. The function of inv/spa genes in maintaining symbiosis is demonstrated by the up-regulation of their expression under both in vivo and in vitro conditions that coincide with host cell invasion.
authors.affiliation: Department of Ecology and Evolutionary Biology, Center for Insect Science, and Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, AZ 85721.
authors.forename: Colin
authors.initials: C
authors.lastname: Dale
authors.forename: Gordon R
authors.initials: GR
authors.lastname: Plague
authors.forename: Ben
authors.initials: B
authors.lastname: Wang
authors.forename: Howard
authors.initials: H
authors.lastname: Ochman
authors.forename: Nancy A
authors.initials: NA
authors.lastname: Moran
mesh_terms: D018829:Adhesins, Bacterial / Q000235:genetics; D000818:Animals; D000942:Antigens, Bacterial / Q000235:genetics; D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D001517:Coleoptera / Q000235:genetics* / Q000382:microbiology* / Q000502:physiology; D004269:DNA, Bacterial / Q000235:genetics; D004755:Enterobacteriaceae / Q000235:genetics* / Q000502:physiology*; D015870:Gene Expression; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D010802:Phylogeny; D013559:Symbiosis / Q000235:genetics*
chemical_list: D018829:Adhesins, Bacterial; D000942:Antigens, Bacterial; D004269:DNA, Bacterial; C119204:streptococcal protective antigen; C053476:invasin, Yersinia