ABSTRACT
L-Tyrosine (Tyr) and its plant-derived natural products are essential in both plants and humans. In plants, Tyr is generally assumed to be synthesized in the plastids via arogenate dehydrogenase (TyrA(a), also known also ADH), which is strictly inhibited by L-Tyr. Using phylogenetic and expression analyses, together with recombinant enzyme and endogenous activity assays, we identified prephenate dehydrogenases (TyrA(p)s, also known as PDHs) from two legumes, Glycine max (soybean) and Medicago truncatula. The identified PDHs were phylogenetically distinct from canonical plant ADH enzymes, preferred prephenate to arogenate substrate, localized outside of the plastids and were not inhibited by L-Tyr. The results provide molecular evidence for the diversification of primary metabolic Tyr pathway via an alternative cytosolic PDH pathway in plants.
