Evaluation of <i>Brachypodium distachyon</i> L-Tyrosine Decarboxylase Using L-Tyrosine Over-Producing <i>Saccharomyces cerevisiae</i>

<div><p>To demonstrate that herbaceous biomass is a versatile gene resource, we focused on the model plant <i>Brachypodium distachyon</i>, and screened the <i>B</i>. <i>distachyon</i> 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 <i>B</i>. <i>distachyon</i> and were introduced into <i>Saccharomyces cerevisiae</i> 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 <i>S</i>. <i>cerevisiae</i> 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 <i>B</i>. <i>distachyon</i> TDC effectively converts L-tyrosine to tyramine. Our results suggest that <i>B</i>. <i>distachyon</i> possesses enzymes that are capable of modifying aromatic residues, and that <i>S</i>. <i>cerevisiae</i> is a suitable host for the production of L-tyrosine derivatives.</p></div

Strains, plasmids, transformants, and oligonucleotide primers used in this study.

<p>Strains, plasmids, transformants, and oligonucleotide primers used in this study.</p

Proposed biosynthesis pathway for tyramine (ARO3, ARO4; 3-deoxy-D-heptulosonate-7-phosphate synthase: ARO7; chorismate mutase: TDC; L-tyrosine decarboxylase).

<p>ARO3, ARO4 and ARO7 are derived from <i>S</i>. <i>cerevisiae</i>, whereas TDC is originated from <i>B</i>. <i>distachyon</i>.</p