1.9.22
ELICITOR-INDUCIBLE EXPRESSION OF THT IN POTATO

S ROSAHL, A SCHMIDT, D SCHEEL and D STRACK

Institute for Plant Biochemistry, Halle, Germany

As part of the plant's response to pathogen attack, cell wall-bound phenolics such as amides of hydroxycinnamic acids and tyramine accumulate, presumably functioning in reinforcement of the cell wall and as antifungal compounds. In potato, treatment of suspension-cultured cells with a crude elicitor preparation of Phytophthora infestans leads to an increase in the activity of tyramine-N-(hydroxycinnamoyl)-transferase (THT), the enzyme catalysing the last step in the synthesis of hydroxycinnamoyltyramines.

Using degenerate primers derived from amino-acid sequences of THT peptides, a THT-specific fragment was obtained by RT-PCR. A cDNA library constructed from RNA of elicited potato cells was screened with the PCR fragment as a probe, and several THT-specific cDNAs were isolated. One clone covering the complete coding region was used for expression of THT in E. coli. Extracts of bacteria containing this clone showed high THT enzyme activity with coumaroyl-CoA and tyramine as substrates. Gel filtration revealed that the active enzyme was a dimer. RNA analyses using the insert of the cDNA clone as a probe showed that in potato cell cultures, elicitor-induced THT transcript accumulation peaks at 5 h after initiation of treatment.