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Systematics Section / ASPT

Robadey, Talline M. [1], Barkman, Todd J. [1].

Distinguishing between parallel and convergent evolution of floral scent in Solanaceae.

The presence of homoplastic traits in unrelated lineages may be explained by either parallel or convergent evolution. In the context of secondary chemicals, the two hypotheses may be strictly defined whereby the convergent evolution of a compound is due to the activity of paralogous enzymes, whereas the production of a chemical trait by the activity of orthologous sequences is due to parallel evolution. The Solanaceae provides an excellent opportunity to test these hypotheses of chemical trait evolution because methyl salicylate (MeSA) evolved in the floral scent of multiple species independently. To evaluate whether parallel or convergent evolution occurred in Solanaceae, we first identified and sequenced two paralogous lineages of carboxyl methyltransferases that have members known to functionally catalyze the synthesis of MeSA. We then assessed tissue-specific levels of expression of the paralogous genes that produce MeSA, salicylic acid methyltransferase (SAMT) and benzoic/salicylic acid methyltransferase (BSMT) in three MeSA producing lineages. SAMT was upregulated in the flowers of Cestrum nocturnum and Datura wrightii and not in Nicotiana suaveolens. The paralogous BSMT sequence was upregulated in Nicotiana suaveolens and Datura wrighti, but not in Cestrum nocturnum. Phylogenetic analyses of the flower-expressed sequences were performed to verify their orthology or paralogy. We tentatively conclude that the ability to produce MeSA in C. nocturnum and N. suaveolens arose by convergence. Further scrutiny of these hypotheses in D.wrightii await biochemical characterization of the SAMT/BSMT sequences.


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1 - Western Michigan University, Department of Biological Sciences, 1903 West Michigan Ave, Kalamazoo, Michigan, 49008, USA

Keywords:
Solanaceae
Convergent evolution
parallel evolution
floral scent
SAMT
methyl salicylate.

Presentation Type: Oral Paper
Session: 48-2
Location: Salon G - Austin Grand Ballroom/Hilton
Date: Wednesday, August 17th, 2005
Time: 1:15 PM
Abstract ID:440


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