Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Biology

Supervisor

Dr. Susanne Kohalmi

Abstract

Phenylalanine (Phe), an essential aromatic amino acid, serves as a precursor for protein synthesis and a variety of secondary metabolites in plants. Two pathways are known for Phe biosynthesis. In the first, prephenate dehydratases (PDTs) convert prephenate to phenylpyruvate, which is transaminated to Phe. In the second, prephenate is transaminated to arogenate, which is converted to Phe by arogenate dehydratases (ADTs). ADTs and PDTs are structurally very similar, as are their substrates. Six ADTs (ADT1-ADT6) have been identified in Arabidopsis thaliana. ADT1 and ADT2 can recognize both prephenate and arogenate as substrates whereas ADT3-ADT6 are solely arogenate-accepting. Twenty ADT domain-swapping chimeras were generated through overlap extension PCR and were tested for PDT function in a pha2 complementation assay. Through targeted mutagenesis it was identified that a single substitution in ADT5 was sufficient to introduce PDT function to this previously solely arogenate-accepting ADT. This research represents the first identification of an amino acid that discriminates an arogenate-only ADT from an ADT that is able to accept prephenate.


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