Potato tubers as bioreactors for palatinose production

Palatinose (isomaltulose, 6-O-alpha-D-glucopyranosyl-D-fructose) is a structural isomer of sucrose with very similar physico-chemical properties. Due to its non-cariogenicity and low calorific value it is an ideal sugar substitute for use in food production. Palatinose is produced on an industrial scale from sucrose by an enzymatic rearrangement using immobilized bacterial cells. To explore the potential of transgenic plants as alternative production facilities for palatinose, a chimeric sucrose isomerase gene from Erwinia rhapontici under control of a tuber-specific promoter was introduced into potato plants. The enzyme catalyses the conversion of sucrose into palatinose. Expression of the palI gene within the apoplast of transgenic tubers led to a nearly quantitative conversion of sucrose into palatinose. Despite the soluble carbohydrates having been altered within the tubers, growth of palI expressing transgenic potato plants was indistinguishable from wild type plants. Therefore, expression of a bacterial sucrose isomerase provides a valid tool for high level palatinose production in storage tissues of transgenic crop plants.