SMALL-SUBUNIT RIBOSOMAL-RNA GENE PHYLOGENY OF PLASMODIOPHORA-BRASSICAE

The small subunit ribosomal RNA genes of Plasmodiophora brassicae, an obligate endoparasite of crucifers, were amplified using the polymeras e chain reaction and found to be approximately 3 kilobases (kb) long. Reverse transcriptase-PCR of the small subunit rRNA produced a fragmen t approximately 1.8 kb long. Insertion sequences were found at positio ns 567 (388 bp), 1195 (383 bp), and 1786 (442 bp) of the P. brassicae small subunit ribosomal DNA. Maximum likelihood phylogenetic analysis of the rDNA sequence suggests that P. brassicae may be more closely re lated to the alveolates (Dinozoa, Ciliophora, and Apicomplexa) than to any of the Fungi, Mycetozoa or Rhizopoda. Bootstrapping (30%), howeve r, does not support this hypothesis, indicating that P. brassicae is n ot very closely related to any of che organisms in this alignment, inc luding those with which it has been classified in the past.