Simultaneous antagonistic modulation of enzyme activities in transgenic plants through the expression of a chimeric transcript

The aim of this work was to investigate the possibility of modulating different enzyme activities in an antagonistic manner using a single transgenic approach. To this end a yeast (Saccharomyces cerevisiae) cDNA encoding for a β-fructosidase (invertase; EC 3.2.1.26) was introduced into a binary vector in the sense orientation directly coupled to a fragment of the cDNA encoding for the small subunit of potato (Solanum tuberosum) AGPase (EC 2.2.7.27) in the antisense orientation. Transgenic plants were generated by Agrobacterium-mediated transfer with the expression of both cDNAs being under the control of the tuber specific B33 patatin promoter. The resulting transformants were screened by analysis of metabolites which are known to change when the targeted enzymes are modulated. Finally, northern analysis coupled with enzymatic analysis revealed that the chimeric gene was expressed and that expression led to both the production of yeast invertase and the antisense repression of the endogenous potato AGPase activity. We therefore conclude that this method will be of use in metabolic engineering strategies that require a simultaneous up-regulation of one pathway and an inhibition of a second competing pathway.