|Lee, Ing Ming|
Submitted to: International Organization for Mycoplasmology
Publication Type: Abstract Only
Publication Acceptance Date: 5/25/2004
Publication Date: 7/11/2004
Citation: Martini, M., Lee, I., Zhao, Y., Botti, S., Bertaccini, A., Carraro, L., Marcone, C., Osler, R. 2004. Ribosomal protein gene-based phylogeny: a basis for phytoplasma classification. International Organization for Mycoplasmology. p. 156.
Technical Abstract: Because of the inability to culture phytoplasmas in vitro and the lack of their phenotypic properties, it is inevitable to base phytoplasma taxonomy largely on phylogeny. The highly conserved 16S rRNA gene sequence has been used as the primary phylogenetic parameter for classification of phytoplasmas in recently emerging phytoplasma taxonomy. However, because of its highly conserved nature, 16S rRNA gene sequence is not the best parameter for differentiation of phytoplasma strains at a taxonomic rank below genus level. Ribosomal protein (rp) genes are among more variable markers that have proved to be useful for finer differentiation of phytoplasma strains in two 16Sr groups. In the present study we designed degenerate primers that allowed for the amplification of rpl22 and rps3 genes from phytoplasma strains representing most phytoplasma groups described so far. A phylogenic tree was constructed based on analysis of rp gene sequences from 53 phytoplasma strains belonging to 11 16Sr phytoplasma groups. The phylogenetic relationships among phytoplasmas were in agreement with those obtained on the basis of 16S rDNA gene in previous works. But rp-based phylogeny allowed finer resolution of distinct lineages or subclades within the phytoplasma clade and it was possible to recognize more distinct phytoplasma subclades than those based on 16S rDNA phylogeny. Moreover, rp genes-based phylogeny seemingly delineated finer phylogenetic relationships among phytoplasma groups than 16S rDNA-based phylogeny. The phylogenetic analysis based on rp gene sequences indicated that OAY and related strains, MPV and related strains, TomStol and AP and related strains, which constituted a major monophyletic group, were the phytoplasma taxa with the closest phylogenetic link to Acholeplasma relatives. A second phylogenetic tree was constructed based on the deduced amino-acid sequences of ribosomal protein L22 and S3 from 53 representative phyoplasma strains, two acholeplasmas, other mollicutes and Gram-positive walled bacteria. The global phylogeny based on deduced amino-acid sequences of ribosomal proteins L22 and S3 revealed that the phytoplasma clade may be constituted of more than one monophyletic group, because phytoplasma strains belonging to 16SrI, 16SrXIII, 16SrXII and 16SrX were clustered together with the two Acholeplasma spp. forming a major phylogenetic group, paraphyletic to the group constituted by the rest of phytoplasmas strains. It was also suggested that phytoplasma and acholeplasma might be more closely related to gram-positive walled bacteria than to other mollicutes such as mycoplasma and spiroplasma. These findings need to be further confirmed by including more mycoplasma taxa. Nevertheless, rp gene sequences represent a valid molecular tool to gain new insights into the phytoplasma phylogeny and taxonomy.