Expression of a bacterial lysine decarboxylase gene and transport of the protein into chloroplasts of transgenic tobacco.

A possible approach for altering alkaloid biosynthesis in plants is the expression of genes encoding key enzymes of a pathway such as lysine decarboxylase (ldc) in transgenic plants. Two strategies were followed here: one focused on expression of the gene in the cytoplasm, the other on subsequent targeting of the protein to the chloroplasts. The ldcgene from Hafnia alvei was therefore (a) placed under the control of the 1' promoter of the bidirectional Tr promoter from Agrobacterium tumefaciens Ti-plasmid, and (b) cloned behind the rbcS promoter from potato fused to the coding region of the rbcS transit peptide. Both ldc constructs, introduced into Nicotiana tabacum with the aid of A. tumefaciens, were integrated into the plant genome and transcribed as shown by Southern and northern hybridization. However, LDC activity was only detectable in plants expressing mRNA under the control of the rbcS promoter directing the LDC fusion protein into chloroplasts with the aid of the transit peptide domain. In plants expressing the processed bacterial enzyme cadaverine levels increased from nearly zero to 0.3-1% of dry mass.