A CHIMERIC TRYPTOPHAN DECARBOXYLASE GENE AS A NOVEL SELECTABLE MARKERIN PLANT-CELLS

A novel selection system for plant genetic transformation was develope d based on the enzyme tryptophan decarboxylase (TDC; EC 4.1.1.28) from Catharanthus roseus. This enzyme converts the toxic tryptophan analog ue 4-methyl tryptophan (4-mT) into the non-toxic compound 4-methyl try ptamine. Expression of tdc in transgenic plants that have no endogenou s TDC-activity allows selection on 4-mT. A vector was constructed cont aining a tdc cDNA clone under control of the constitutively expressed cauliflower mosaic virus 35S promoter. This vector was used in Agrobac terium-mediated tobacco leaf disc transformation experiments. The opti mal concentration for selection with 4-mT was found to be 0.1 mM. The transformed nature of shoots obtained after tdc gene transfer and subs equent selection on 0.1 mM 4-MT was confirmed by northern blot analysi s.