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Title: NEW GROUP 16SRIII PHYTOPLASMA LINEAGES IN LITHUANIA EXHIBIT RRNA INTEROPERON SEQUENCE HETEROGENEITY

Author
item JOMANTIENE, R - INST OF BOTANY LITHUANIA
item Davis, Robert
item VALIUNAS, D - INST OF BOTANY LITHUANIA
item ALMINAITE, A - INST OF BOTANY LITHUANIA
item STANIULIS, J - INST OF BOTANY LITHUANIA

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Phytoplasmas are minute, cell wall-less bacterial pathogens that cause diseases in hundreds of plants species worldwide. Numerous are of quarantine/phytosanitary concern. It is important to develop molecular markers for their rapid detection and identification in order facilitate quarantines designed to prevent their introduction into new regions. Since it is not possible to isolate any phytoplasma in pure culture, characteristics used for detection, identification, and classification of other bacteria cannot be used for identification and classification of phytoplasmas. In this study, a new host (Gaillardia sp.) of aster yellows phytoplasma was revealed, and two previously undescribed phytoplasmas were discovered in diseased plants of dandelion and Cirsium sp. The two phytoplasmas discovered in dandelion and Cirsium sp. were each found to contain two sequence heterogeneous 16S rRNA genes. This work provides molecular markers whereby phytoplasmas may be detected and identified, thereby facilitating studies in epidemiology and disease control and efforts in plant quarantine. The characterization of the sequence heterogeneous 16S rRNA genes supports the need for characterization of both rRNA operons for identification and phylogeny of the phytoplasma genome. The findings will be of interest to scientists, plant disease diagnosticians, and quarantine/phytosanitary agencies involved in fundamental studies of and detection and interception of exotic pathogens.

Technical Abstract: Previously undescribed phytoplasmas were detected in diseased plants of dandelion (Taraxacum officinale) exhibiting virescence of flowers, thistle (Cirsium arvense) exhibiting symptoms of white leaf, and Gaillardia sp. exhibiting symptoms of stunting and phyllody in Lithuania. On the basis of RFLP analysis of 16S rDNA amplified in PCR, the dandelion virescence (Dan Vir), cirsium whiteleaf (CirWL), and gaillardia phyllody (GaiPh) phytoplasmas were classified in phylogenetic group 16SrIII (X-disease phytoplasma group), new subgroups III-P and III-R and subgroup III-B, respectively. RFLP and nucleotide sequence analyses revealed 16S rRNA interoperon sequence heterogeneity in the two rRNA operons, rrnA and rrnB, of both Dan Vir and CirWL. Results from phylogenetic analysis based on nucleotide sequences of 16S rDNA were consistent with recognition of the two new subgroups as representatives of distinct new lineages within the group 16SrIII phytoplasma subclade. The branching order of rrnA and rrnB sequences in the phylogenetic tree supported this interpretation and indicated recent common ancestry of the two rRNA operons in each of the phytoplasmas exhibitng interoperon heterogeneity.