Investigating the biochemistry of phenylpropanoid metabolism in basil and petunia
Abstract
Land plants are, in general, immobile organisms. This sedentary lifestyle leaves them vulnerable to a wide variety of adversity, thus an even wider variety of adaptations must be made to ensure successful reproduction. Plant secondary metabolites, of which more than 100,000 structures have been described to date, represent plant life's attempt to cope with demanding environments encountered globally. Volatile secondary metabolites enable plants to boost reproductive efficiency and genetic diversity through attraction of pollinators, provide constitutive and inducible defenses against attack from herbivores and pathogens, mitigate abiotic stresses encountered in nature, increase species’ distribution via enticement of seed dispersers, and even warn neighboring plants of danger from pests and pathogens. Working in basil and petunia, my research has characterized two critical steps in secondary metabolism. Many basil cultivars as well as other plant taxa produce the volatile compound methyl cinnamate. In basil, this compound is produced via transfer of a reactive methyl group from S-adenosyl methionine to the carboxyl group of trans-cinnamic acid, a reaction catalyzed by cinnamate/p-coumarate carboxylmethyltransferase (CCMT) enzymes. These enzymes are localized within the pelatate glandular trichomes of basil leaves and have somewhat broad substrate specificity towards small carboxylic acids. Amino acid residues determining substrate specificity of these enzymes were probed using site directed mutagenesis and novel activity with additional carboxylic acids was engineered in a mutant form of one CCMT isoform. In petunia, the phenylpropene isoeugenol makes up a significant portion of emitted volatile compounds from floral tissues. Recent work described formation of isoeugenol and its positional isomer eugenol from the compound coniferyl acetate however the reaction forming coniferyl acetate from its precursor coniferyl alcohol was undescribed. Investigation of this step included isolation of the candidate gene, gene expression profiling, and biochemical characterization of the recombinant enzyme.
Degree
Ph.D.
Advisors
Dudareva, Purdue University.
Subject Area
Horticulture|Plant biology
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