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Submitted to: American Phytopathological Society
Publication Type: Abstract Only Publication Acceptance Date: 5/15/2004 Publication Date: 6/1/2004 Citation: Zhao, Y., Davis, R.E., Lee, I. 2004. Phylogenetic analysis based on multiple sets of concatenated proteins suggests earlier ancestors for phytoplasmas. American Phytopathological Society. 94(s):116. Interpretive Summary: Technical Abstract: Phytoplasmas are cell wall-less, nonculturable bacteria that cause diseases in several hundred plant species. Phytoplasmas are classified as Mollicutes and have been thought to be evolved retrogressively from ancestral low G+C Gram-positive bacteria of the Bacillus/Clostridium group. Since phytoplasmas parasitize both plant hosts and insect vectors, knowledge of phytoplasma evolution is important to understand their parasitic life style and pathogenicity. In this study, the evolutionary relationship between phytoplasmas and other micro-organisms were investigated using a comparative genomics approach. More than 50 evolutionarily conserved proteins that are ubiquitous to all bacteria were selected to build a consensus tree. These proteins were concatenated into five superproteins and phylogenetic trees were reconstructed based on the five superproteins using both Maximum likelihood and parsimony methods. A total of 40 bacterial species were used for the analysis. The topologies of the five trees are congruent in that phytoplasmas are clustered together with other Mollicutes, forming a monophyletic group. In all five trees, Bacillaceae, along with Lactobacillales, is paraphyletic to Mollicutes, rather than being ancestral. It appears that an unknown common ancestor gave rise to two sister clades, Bacillus/Mollicutes and Clostridia. This suggests that phytoplasmas may have evolved earlier than previously thought. Our results also revealed possible events of horizontal gene acquisition in early stages of mollicute evolution. |
