|Lee, Ing Ming|
Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2004
Publication Date: 1/1/2005
Citation: Lee, I., Martini, M., Marcone, C., Zhu, S.F. 2004. Classification of elm yellows group (16SrV) phytoplasmas and proposition of 'Candidatus Phytoplasma ulmi' for the elm yellows phytoplasma and 'Candidatus Phytoplasma chinense' for the cherry lethal yellowing phytoplasma. International Journal of Systematic and Evolutionary Microbiology. 54:337-347
Interpretive Summary: Phytoplasmas are very small bacteria that lack a cell wall and that cause economically important diseases in plants including elm, grapevine, blackberry, cherry, peach and forest trees. The different phytoplasmas attacking these plants are closely related to each other, and it has been difficult to distinguish them from one another. We studied three different genes in the phytoplasmas, two genes involved in protein synthesis and the third involved in secretion of proteins from inside to the outside of the phytoplasma cell. Combined analysis of these genes revealed that phytoplasmas attacking elm and phytoplasmas attacking cherry are distinct from one another and from related phytoplasmas. As a result, we have proposed naming the phytoplasma attacking elm and the phytoplasma attacking cherry as two different species, respectively. The information in this paper will aid implementation of quarantine regulations internationally, and it will help extension workers and plant diagnosticians to determine how to combat the diseases in elm and cherry.
Technical Abstract: Elm yellows (EY) group (16SrV) phytoplasmas associated with devastating diseases in elm, grapevine, blackberry, cherry, peach and several other plant species in America, Europe and Asia represents one of the most diverse phytoplasma clusters. Based on phylogenetic analysis of 16S rDNA sequences, EY group phytoplasmas form a discrete subclade within the phytoplasma clade. We have evaluated three phylogenetic parameters, 16S rRNA, ribosomal protein (rp), and secY genes for their usefulness in differentiating EY group phytoplasmas. RFLP analysis of 16S rRNA sequences differentiated the EY group into 5 subgroups. Twelve RFLP subgroups were differentiated based on rp and 13 based on secY gene sequences. Phylogenetic analysis of rp genes, or rp and secY genes indicated that the subgroups constitute six genetically distinct strain clusters. Each cluster appeared to have evolved under different ecological constraints such as specific vector or plant hosts. On the basis of unique DNA and biological properties, it is proposed that the elm yellows phytoplasma represents a new taxon, 'Candidatus Phytoplasma ulmi', and that the cherry lethal yellowing phytoplasma represents another new taxon, 'Candidatus Phytoplasma chinense'.