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J. Eukaryot. Microbiol., 51(1), 2004 pp. 113118 2004 by the Society of Protozoologists

Summary: 113
J. Eukaryot. Microbiol., 51(1), 2004 pp. 113118
2004 by the Society of Protozoologists
Actin and Ubiquitin Protein Sequences Support a Cercozoan/Foraminiferan
Ancestry for the Plasmodiophorid Plant Pathogens
Canadian Institute for Advanced Research, Program in Evolutionary Biology, Department of Botany, University of British Columbia,
3529-6270 University Blvd., Vancouver, British Columbia, V6T 1Z4, Canada
ABSTRACT. The plasmodiophorids are a group of eukaryotic intracellular parasites that cause disease in a variety of economically
significant crops. Plasmodiophorids have traditionally been considered fungi but have more recently been suggested to be members of
the Cercozoa, a morphologically diverse group of amoeboid, flagellate, and amoeboflagellate protists. The recognition that Cercozoa
constitute a monophyletic lineage has come from phylogenetic analyses of small subunit ribosomal RNA genes. Protein sequence data
have suggested that the closest relatives of Cercozoa are the Foraminifera. To further test a cercozoan origin for the plasmodiophorids,
we isolated actin genes from Plasmodiophora brassicae, Sorosphaera veronicae, and Spongospora subterranea, and polyubiquitin gene
fragments from P. brassicae and S. subterranea. We also isolated actin genes from the chlorarachniophyte Lotharella globosa. In protein
phylogenies of actin, the plasmodiophorid sequences consistently branch with Cercozoa and Foraminifera, and weakly branch as the
sister group to the foraminiferans. The plasmodiophorid polyubiquitin sequences contain a single amino acid residue insertion at the
functionally important processing point between ubiquitin monomers, the same place in which an otherwise unique insertion exists in
the cercozoan and foraminiferan proteins. Taken together, these results indicate that plasmodiophorids are indeed related to Cercozoa
and Foraminifera, although the relationships amongst these groups remain unresolved.


Source: Archibald, John - Department of Biochemistry and Molecular Biology, Dalhousie University
Keeling, Patrick - Department of Botany, University of British Columbia


Collections: Biology and Medicine; Environmental Sciences and Ecology