Ketocarotenoid formation in transgenic potato.

Potato has been genetically engineered for the production of commercially important ketocarotenoids including astaxanthin (3,3'-dihydroxy 4,4'-diketo-beta-carotene). To support the formation of 3-hydroxylated and 4-ketolated beta-carotene, a transgenic potato line accumulating zeaxanthin due to inactivated zeaxanthin epoxidase was co-transformed with the crtO beta-carotene ketolase gene from the cyanobacterium Synechocystis under a constitutive promoter. Plants were generated which exhibited expression of this gene, resulting in an accumulation of echinenone, 3'-hydroxyechinenone, and 4-ketozeaxanthin in leaves, as well as 3'-hydroxyechinenone, 4-ketozeaxanthin together with astaxanthin in the tuber. The amount of ketocarotenoids formed represent approximately 10-12% of total carotenoids in leaves and tubers. Negative effects on photosynthesis due to the presence of the ketocarotenoids in leaves could be excluded by the determination of variable fluorescence.