Cloning and characterization of a hydroxycinnamoyl-CoA : tyramine N-(hydroxycinnamoyl)transferase induced in response to UV-C and wounding from Capsicum annuum

Hydroxycinnamoyl-CoA : tyramine N-(hydroxycinnamoyl) transferase (THT) is a pivotal enzyme in the synthesis of N-(hydroxycinnamoyl)-amines, which are associated with cell wall fortification in plants. The cDNA encoding THT wa s cloned from the leaves of UV-C treated Capsicum annuum (hot pepper) using a differential screening strategy. The predicted protein encoded by the TH T cDNA is 250 amino acids in length and has a relative molecular mass of 28 ,221, The protein sequence derived from the cDNA shares 76% and 67% identit y with the potato and tobacco THT protein sequences, respectively, The reco mbinant pepper THT enzyme was purified using a bacterial overexpression sys tem, The purified enzyme has a broad substrate specificity including acyl d onors such as cinnamoyl-, sinapoyl-, feruloyl-, caffeoyl-, and 4-coumaroyl- CoA and accepters such as tyramine and octopamine. In UV-C treated plants, the THT mRNA was strongly induced in leaves, and the elevated level of expr ession was stable for up to 36 h, THT mRNA also Increased in leaves that we re detached from the plant but not treated with UV-C, THT expression was me asured in different plant tissues, and was constitutive at a similar level in leaf, root, stem, flower and fruit. Induction of TWT mRNA was correlated with an increase in THT protein.