Date of Defense
4-28-2026
Date of Graduation
5-2026
Department
Biological Sciences
First Advisor
Todd Barkman
Second Advisor
Yan Lu
Abstract
Plant specialized metabolism is shaped by enzyme families that evolve new substrate preferences and biochemical function over time. The SABATH methyltransferase family includes xanthine methyltransferases (XMTs), a clade associated with xanthine alkaloid metabolism and caffeine biosynthesis in some plant lineages. However, the evolutionary history of the XMT clade and the origin of caffeine biosynthetic capability remain unclear. This thesis investigated XMT evolution using phylogenetic analysis and biochemical assays of selected modern and ancestral enzymes. Candidate XMT sequences were identified across major plant lineages and used to generate a phylogenetic tree, while modern XMTs from Mangifera and Malus and reconstructed ancestral enzymes were tested for substrate preference using the MTase-Glo methyltransferase assay. The phylogeny supported the presence of two XMT clades, consistent with an ancient gene duplication event. Modern enzymes showed some divergent substrate preferences, with Mangifera methylating aromatic acids and Malus showing high specificity toward salicylic acid. The ancestral XMTs showed little to no activity with xanthine alkaloids, suggesting this activity was unlikely to be ancestral. Overall, these findings support a model where XMTs diversified after gene duplication, with caffeine biosynthetic capability evolving convergently in separate plant lineages.
Recommended Citation
Hagenbarth, Brenna, "Evolutionary Retention and Functional Divergence of Xanthine Methyltransferases in the SABATH Gene Family" (2026). Honors Theses. 4031.
https://scholarworks.wmich.edu/honors_theses/4031
Access Setting
Honors Thesis-Restricted
Restricted to Campus until
6-5-2028