Date of Award

4-2012

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Dr. Todd J. Barkman

Second Advisor

Dr. Brian C. Tripp

Third Advisor

Dr. Yirong Mo

Fourth Advisor

Dr. Pamela Hoppe

Access Setting

Masters Thesis-Open Access

Abstract

Gene duplication is believed to be the major source for providing genetic materials for the innovation and diversification of protein functions; natural selection and/or neutral drift then works on these genetic materials to guide their evolutionary directions. Here, I used the salicylic acid/benzoic acid/theobromine (SABATH) multigene family to study how natural selection acted on duplicated genes to prompt functional diversification. Members in this family methylate plant secondary metabolites by transferring the methyl group from S-adenosyl-L-methionine (SAM) to the carboxyl group or ring nitrogen of the substrates. In the Apocynaceae and Solanaceae lineage of this family, I documented three putative gene duplication events. For each duplication event, I monitored the functional changes of descendents by biochemically characterizing the functions of phylogenetically resurrected ancestors, and used statistical analysis to detect if any sites were under positive selection along these daughter lineages. I also performed forward and reverse mutagenesis studies to validate the impacts of statistically predicted positively selected sites and explained the substrate specificity changes in terms of enzyme kinetics. In addition, the evolutionary pattern of each duplication event was used to fit the contemporary theoretical models for gene duplication and divergence.

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