Candidcatus Phytoplasma, a taxon for the wall-less, non-helical prokaryotes that colonize plant phloem and insects

• Author(s): Andersen, M.; Bertaccini, A.; Boudon, E.; Bove, J.; Daire, X.; Davis, R.; Firrao, G.; Fletcher, J.; Garnier, Monique; Gibb, K.; Gundersen-Rindal, D.; Harrison, N.; Hiruki, C.; Jones, P.; Kirkpatrick, Bruce; Kuske, C.; Lee, I.; Liefting, L.; Marcone, C.; Namba, S.; Schneider, B.;
• Abstract: The trivial name phytoplasma has been adopted to collectively name wall-less, non-helical prokaryotes that colonize plant phloem and insects, which were formerly known as mycoplasma-like organisms. Although phytoplasmas have not yet been cultivated in vitro, phylogenetic analyses based on various conserved genes have shown that they represent a distinct, monophyletic clade within the class Mollicutes. It is proposed here to accommodate phytoplasmas within the novel genus Candidatus (Ca.) Phytoplasma. Given the diversity within Ca. Phytoplasma, several subtaxa are needed to accommodate organisms that share 97-5% similarity among their 16S rRNA gene sequences. This report describes the properties of Ca. Phytoplasma, a taxon that includes the species Ca. Phytoplasma aurantifolia (the prokaryote associated with witches-broom disease of small-fruited acid lime), Ca. Phytoplasma australiense (associated with Australian grapevine yellows), Ca. Phytoplasma fraxini (associated with ash yellows), Ca. Phytoplasma japonicum (associated with Japanese hydrangea phyllody), Ca. Phytoplasma brasiliense (associated with hibiscus witches-broom in Brazil), Ca. Phytoplasma castaneae (associated with chestnut witches-broom in Korea), Ca. Phytoplasma asteris (associated with aster yellows), Ca. Phytoplasma mali (associated with apple proliferation), Ca. Phytoplasma phoenicium (associated with almond lethal disease), Ca. Phytoplasma trifolii (associated with clover proliferation), Ca. Phytoplasma cynodontis (associated with Bermuda grass white leaf), Ca. Phytoplasma ziziphi (associated with jujube witches-broom), Ca. Phytoplasma oryzae (associated with rice yellow dwarf) and six species-level taxa for which the Candidatus species designation has not yet been formally proposed (for the phytoplasmas associated with X-disease of peach, grapevine flavescence doree, Central American coconut lethal yellows, Tanzanian lethal decline of coconut, Nigerian lethal decline of coconut and loofah witches-broom, respectively). Additional species are needed to accommodate organisms that, despite their 16S rRNA gene sequence being 97.5% similar to those of other Ca. Phytoplasma species, are characterized by distinctive biological, phytopathological and genetic properties. These include Ca. Phytoplasma pyri (associated with pear decline), Ca. Phytoplasma prunorum (associated with European stone fruit yellows), Ca. Phytoplasma spartii (associated with spartium witches-broom), Ca. Phytoplasma rhamni (associated with buckthorn witches-broom), Ca. Phytoplasma allocasuarinae (associated with allocasuarina yellows), Ca. Phytoplasma ulmi (associated with elm yellows) and an additional taxon for the stolbur phytoplasma. Conversely, some organisms, despite their 16S rRNA gene sequence being 97-5% similar to that of any other Ca. Phytoplasma species, are not presently described as Candidatus species, due to their poor overall characterization.
• Publication Date: Jul 2004
• Journal: International Journal Of Systematic And Evolutionary Microbiology