Molecular characterization of the arogenate dehydratase family of Arabidopsis thaliana

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Phenylalanine (Phe), tyrosine and tryptophan are the only amino acids containing an aromatic ring structure. As amino acids they are building blocks of life as they are the basic units for all proteins. Therefore they serve as the molecular and functional backbone of any enzymatic reaction within a cell. In plants these aromatic amino acids also serve as precursors to many secondary metabolites including flavonoids, lignins, melanins, phenols and tannins. As such they contribute to the plant's structural support, pigmentation, scent formation, protection from UV light and predators. Arogenate dehydratases (ADTs) are catalyzing the last step in Phe biosynthesis and represent the key regulatory step for producing Phe. We are proposing a detailed molecular analysis of the six ADT genes and their six corresponding proteins in Arabidopsis, a representative model organism for plants. We predict that having that many similar but not identical enzymes allows this plant to regulate the synthesis of Phe in response to its many uses and that the ability to regulate the activity of these enzymes by internal and environmental cues is essential to the plant's ability to thrive and to survive. Regulation is a highly complex process which requires a network of actions on many molecular levels. By learning how the regulation of ADTs is accomplished, we will provide a fundamental understanding of how the various members of this ADT family contribute to deliver Phe to essential pathways. As Phe serves as a precursor to many secondary metabolites, understanding the role that ADTs play in aromatic amino acid synthesis can have far-reaching significance for basic and applied research. For example, if one can generally increase Phe levels in plants, these plants could be used as food with an increased nutrient value for humans and animals. Alternatively, by knowing how ADTs regulate the shuttling of Phe into downstream pathways one could make plants with lower lignin content (useful if these plants are used for paper production), increase the production of certain flavonoids (this could increase the health benefit as flavonoids have been linked to anti cancer properties), or increase components which give plants the ability to defend themselves against pests and crop diseases.