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United States Department of Agriculture

Agricultural Research Service

Research Project: GENOME SEQUENCE-BASED STRATEGIES FOR DETECTION & IDENTIFICATION OF PLANT PATHOGENIC PHYTOPLASMAS & SPIROPLASMAS, & VASCULAR WALLED BACTERIA

Location: Molecular Plant Pathology

Title: Family acholeplasmataceae (including phytoplasmas)

Authors
item Martini, Marta -
item Marcone, Carmine -
item Lee, Ing Ming
item Firrao, Giuseppe -

Submitted to: Springer Verlag
Publication Type: Book / Chapter
Publication Acceptance Date: September 20, 2013
Publication Date: N/A

Interpretive Summary: Phytoplasmas and its close relatives, acholeplasmas are cell wall-less bacteria. The two groups of microorganisms are associated with different habitats and ecology. Phytoplasmas are uncultivable insect-transmitted plant pathogens associated with more than a thousand diseases including many economically important ones. They represent a new category of plant pathogens. The advance in modern molecular-based tools has made it feasible to identify and classify these uncultivable plant pathogens. In this book chapter we described 36 proposed phytoplasma species and 14 acholeplasma species and the diseases they cause. We also described the phylogenetic relationships among these species which were analyzed using ribosomal RNA and other gene sequences. The information will be used by scientific communities, quarantine regulators, and plant diagnosticians to identify the phytoplasmas and to determine how to combat the diseases they cause.

Technical Abstract: The family Acholeplasmataceae was originally established to accommodate the genus Acholeplasma, comprising the mollicutes that could be cultivated without the supplement of cholesterol and that use UGA as a stop codon instead of coding for tryptophan. It was later shown that the phytoplasmas, a large group of uncultivable, wall less, non helical mollicutes that are associated with plants and insects, shared taxonomically relevant properties with members of the genus Acholeplasma. Being not cultivable in vitro in axenic culture, the phytoplasmas could not be classified using the standards used for other mollicutes and are named using the category of Candidatus, as 'Ca. Phytoplasma'. Although phytoplasmas are associated with habitats and ecology different from acholepalsmas, the two genera Acholeplasma and 'Candidatus Phytoplasma' are phylogenetically related and form a distinct clade within the Mollicutes. The persisting inability to grow the phytoplasmas in vitro hinders the identification of their distinctive phenotypic traits, important criteria for mollicute classification. Until supplemental phenotypic traits become available, the genus 'Candidatus Phytoplasma', is designated, on the basis of phylogeny, as a tentative member in the family Acholeplasmataceae. Phylogenetic analysis based on gene sequences, in particular, ribosomal sequences, has provided the major supporting evidence for the composition and taxonomic subdivision of this group of organisms with diverse habitats and ecology and has become the mainstream for the Acholeplasmataceae systematics. However, without the ability to determine phenotypic properties, the circumscription of related species among the non culturable members of the family remains a major issue. The genus Acholeplasma comprises 14 species predominantly associated with animals and isolated from mammalian fluids but regarded as not normally pathogenic. Conversely, the genus 'Ca. Phytoplasma' includes plant pathogens of major economic relevance worldwide. To date, 36 'Ca. Phytoplasma species' have been described.

Last Modified: 4/20/2014
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