Article

Planta

, Volume 185, Issue 2, pp 148-152

First online:

Expression of enzymatically active and correctly targeted strictosidine synthase in transgenic tobacco plants

  • Thomas D. McKnightAffiliated withDepartment of Biology, Texas A&M University
  • , Daniel R. BergeyAffiliated withDepartment of Biology, Texas A&M University
  • , Ronald J. BurnettAffiliated withDepartment of Biology, Texas A&M University
  • , Craig L. NesslerAffiliated withDepartment of Biology, Texas A&M University

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Abstract

Strictosidine, a precursor to over 1000 indole alkaloids including the anti-tumor drugs vinblastine, vincristine, and camptothecin, is produced by the condensation of tryptamine and secologanin. Strictosidine synthase, the enzyme responsible for this condensation, is the first committed step in the indole-alkaloid pathway. We have introduced a modified cDNA encoding Strictosidine synthase from Catharanthus roseus (L.) Don. (McKnight et al. 1990, Nucl. Acids Res. 18, 4939) driven by the CaMV 35S promoter into tobacco (Nicotiana tabacum L.). Transgenic tobacco plants expressing this construct had from 3 to 22 times greater strictosidinesynthase activity than C. roseus plants. Ultrastructural immunolocalization demonstrated that strictosidine synthase is a vacuolar protein in C. roseus and is correctly targeted to the vacuole in transgenic tobacco. Immunoblot analysis of strictosidine synthase showed that two distinct forms of the enzyme were produced in transgenic tobacco plants but that only a single form was made in C. roseus. This observation indicates that the second form of the protein is not simply a result of overexpression in tobacco, but may reflect differences in protein processing between tobacco and C. roseus.

Key words

Camptothecin Catharanthus Indole alkaloids Nicotiana (transgenic) Protein processing and targeting Strictosidine synthase Vacuole (strictosidine synthase)