Expression Patterns and Functional Analysis of Three SmTAT Genes Encoding Tyrosine Aminotransferases in Salvia miltiorrhiza .

Tyrosine aminotransferase (TAT, E.C. 2.6.1.5) is a pyridoxal phosphate-dependent aminotransferase that is widely found in living organisms. It catalyzes the transfer of the amino group on tyrosine to α-ketoglutarate to produce 4-hydroxyphenylpyruvic acid (4-HPP) and is the first enzyme for tyrosine degradation. Three SmTATs have been identified in the genome of Salvia miltiorrhiza (a model medicinal plant), but their information is very limited. Here, the expression profiles of the three SmTAT genes ( SmTAT1 , SmTAT2 , and SmTAT3 ) were studied. All three genes expressed in different tissues and responded to methyl jasmonate stimuli. Sm TAT proteins are localized in the cytoplasm. The recombinant Sm TATs were subjected to in vitro biochemical properties. All three recombinant enzymes had TAT activities and Sm TAT1 had the highest catalytic activity for tyrosine, followed by Sm TAT3. Also, Sm TAT1 preferred the direction of tyrosine deamination to 4-HPP, while Sm TAT2 preferred transamination of 4-HPP to tyrosine. In parallel, transient overexpression of SmTATs in tobacco leaves revealed that all three Sm TAT proteins catalyzed tyrosine to 4-HPP in vivo, with Sm TAT1 exhibiting the highest enzymatic activity. Overall, our results lay a foundation for the production of tyrosine-derived secondary metabolites via metabolic engineering or synthetic biology in the future.