Dorman, Hanna Elizabeth , Wallace, Lisa .
Genetic Structure of Rhizobia Associated with Chamaecrista fasciculata.
Legumes and nitrogen-fixing rhizobia are the partners of an important endosymbiotic relationship. These symbioses are thought to be highly specific; however, recent studies have found that the functionality of symbiotic specificity can vary among plants of the same species, among rhizobial strains and in concert with geographical variation. It is unclear whether these patterns of specificity are due to plant choice or rhizobia availability in differing environments. Here, we examined the diversity and geographic structure of rhizobia nodulating Chamaecrista fasciculata. Chamaecrista fasciculata grows throughout the east and central U.S. and exhibits substantial intraspecific morphological variation, leading some botanists to recognize multiple taxa. Bradyrhizobium elkanii was identified as the only symbiont in some northern populations, but experimental studies show that symbioses with other rhizobia may be possible. We tested the hypothesis of local turnover of rhizobia in nodules of C. fasciculata across habitats throughout Mississippi and sought to determine whether soil characteristics or geography were strong predictors of nodulating rhizobia diversity. We also evaluated potential for variation in rhizobia housed in different nodules of individual plants. From soil samples, we measured pH, P, K, Ca, S, Na, Fe, Mn, Zn, and Cu, and we characterized rhizobia diversity by DNA sequencing of two genes. Soil characters were compared to genetic variation of rhizobia using a partial Mantel test that controlled for geographic distance among sampling sites. Bradyrhizobium was the only genus of rhizobia found in the nodules of C. fasciculata, but we identified isolates that resembled multiple Bradyrhizobium species. A network analysis of genotypes revealed genetic structuring among rhizobia isolates; however this structure did not coincide with geography of sampled areas, and soil properties were not strong predictors of rhizobia diversity at the local level. Species-level differences in rhizobia were found across nodules of individual plants. These results suggest that C. fasciculata is a generalist within Bradyrhizobium, although studies of the adaptive nature of such relationships as well as characterization of rhizobia across the range of C. fasciculatata are needed to confirm this conclusion. Such a generalist pattern may facilitate the colonization of populations of C. fasciculata and contribute to its wide distribution.
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1 - Mississippi State University, PO Box GY, Mississippi State, MS, 39762, USA
Presentation Type: Poster:Posters for Sections
Location: Hall D/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 5:30 PM
Candidate for Awards:Ecological Section Best Graduate Student Poster