Submitted to: International Organization for Mycoplasmology
Publication Type: Abstract Only
Publication Acceptance Date: May 25, 2004
Publication Date: July 11, 2004
Citation: Lee, I., Zhao, Y., Bottner, K.D. 2004. Phylogenetic analysis and classification of aster yellows group(16 sr i) phytoplasmas based on secy gene sequences. International Organization for Mycoplasmology. p. 126-127 Technical Abstract: Aster yellows (AY) group (16SrI) phytoplasmas are associated with more than 100 economically important diseases worldwide and represent the most diverse and widespread phytoplasma group. Based on phylogenetic analysis of 16S rDNA sequences, AY group phytoplasmas form a discrete subclade within the phytoplasma clade. We have evaluated phylogenetic parameters for use in differentiating AY group phytoplasmas. Phylogenetic analysis of secY gene sequences resolved 10 genetically distinct lineages. In general, each distinct lineage appeared to have evolved under different ecological constraints such as specific vectors or plant hosts. The 10 lineages coincide with those delineated by phylogenetic analysis based on ribosomal protein (rp) gene sequences. However, greater genetic variability among the 10 lineages was revealed based on secY gene sequences. The distinct phylogenetic lineages can be readily identified through restriction fragment length polymorphism (RFLP) analysis of secY gene sequences. Ten subgroups were differentiated among the AY group phytoplasmas based on RFLP analysis of secY gene sequences. Phylogenetic analysis based on secY gene sequences in this and previous studies and on the 16S rRNA gene, tuf gene, and rp gene sequences reinforced the notion that most subgroups identified by RFLP analysis of secY and rp gene sequences represent distinct phylogenetic lineages. Moreover, many subgroups occupy uniquely different ecological niches in nature and are associated with specific plant and insect hosts and/or are restricted to isolated geographical regions. Currently, 'Candidatus Phytoplasma asteris' has been proposed to represent the entire AY group phytoplasma. In light of the substantial genetic variability and differences in biological properties among the diverse AY group phytoplasmas, it seems justified to assign more than one 'Candidatus Phytoplasma' species in the AY group.