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Systematics Section / ASPT

Vanden Heuvel, Brian [1], Potter, Daniel [2], Benson, David [3].

Direct characterization of uncultured Group 1 Frankia diversity from the rhizoshere of Chamaebatia foliolosa (Rosaceae), Datisca glomerata (Datiscaceae), and Ceanothus spp. (Rhamnaceae).

Frankia, a filamentous nitrogen-fixing soil bacteria (actinomycete), forms nitrogen-fixing root nodules with at least 200 species of woody plants, representing 24 genera, in 8 plant families. Frankia biodiversity is currently broken into three major groups based on well supported clades, referred to as group 1, 2, and 3. Frankia strains belonging to group 1 associate with plants from the Rosaceae, Ceanothus, the Datiscaceae, and the Coriariaceae. We undertook a study to sample and describe Group 1 Frankia population diversity, present in the rhizoshere of Group 1 plant hosts, and compare it to the diversity previously found in nodules. Studies of Frankia strain diversity in nodules of Group 1 Frankia hosts have revealed low levels of strain diversity and no host specificity. Factors that may account for the observed lack of genetic variability and host specificity include: strain dominance over a large geographic area, current selection by the host plants, and/or a past evolutionary bottleneck. DNA was extracted from soil collected at three sites in central California. A nested PCR strategy was developed to target the variable region of the glutamine synthetase gene (glnA). We found that most of the cloned Frankia glnA sequences obtained from the soil DNA amplification (96%-98%) were identical or closely related to the sequences previously derived from nodule tissue collected from the host plants at the same sites. Only 2-4 percent of glnA sequences derived from cloned soil amplifications and characterized as Frankia Group 1 strains were divergent from the nodule strains. These results confirm the previous findings of low variability in nodules, and support the hypothesis that the absence of variation and host specificity we find in Group 1 Frankia host nodule tissue is the result of strain dominance over a large geographic area.

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1 - Colorado State University - Pueblo, Biology, 2200 Bonforte Bvld., Pueblo, Colorado, 80906, USA
2 - University of California, Davis, Pomology, One Shields Ave., Davis, California, 95616, USA
3 - University of Connecticut, Molecular & Cell Biology, 91 N. Eagleville Rd., U-3125, Storrs, Connecticut, 06269-3125, USA

genetic diversity.

Presentation Type: Poster
Session: 33-112
Location: Salon C, D & E - Gov Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 12:30 PM
Abstract ID:322

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