Evaluation of Brachypodium distachyon L-Tyrosine Decarboxylase Using L-Tyrosine Over-Producing Saccharomyces cerevisiae

To demonstrate that herbaceous biomass is a versatile gene resource, we focused on the model plant Brachypodium distachyon , and screened the B . distachyon for homologs of tyrosine decarboxylase (TDC), which is involved in the modification of aromatic compounds. A total of 5 candidate genes were identified in cDNA libraries of B . distachyon and were introduced into Saccharomyces cerevisiae to evaluate TDC expression and tyramine production. It is suggested that two TDCs encoded in the transcripts Bradi2g51120.1 and Bradi2g51170.1 have L-tyrosine decarboxylation activity. Bradi2g51170.1 was introduced into the L-tyrosine over-producing strain of S . cerevisiae that was constructed by the introduction of mutant genes that promote deregulated feedback inhibition. The amount of tyramine produced by the resulting transformant was 6.6-fold higher (approximately 200 mg/L) than the control strain, indicating that B . distachyon TDC effectively converts L-tyrosine to tyramine. Our results suggest that B . distachyon possesses enzymes that are capable of modifying aromatic residues, and that S . cerevisiae is a suitable host for the production of L-tyrosine derivatives.