Pathway engineering of plants toward astaxanthin production

Astaxanthin responsible for the red color of red fish and crustacean has beneficial effects on human health as well as its utility as a pigmentation source in aquaculture. Astaxanthin biosynthetic pathway from b-carotene needs two enzymes, a carotenoid 4,4 -ketolase (oxygenase) and a carotenoid 3,3 -hydroxylase. b-Carotene is usually one of dominant carotenoids in higher plants, which lack the former enzyme. This mini-review elucidates in the earlier section the catalytic functions of a series of the ketolase and hydroxylase enzymes that have been isolated up to now. For the last ten years, pathway engineering approaches of plants including staple crops toward astaxanthin production have been undertaken by introducing and expressing in the plants a ketolase gene sometimes along with a hydroxylase gene. Several successful results have been achieved to produce large amounts of astaxanthin together with other ketocarotenoids in plant tissues such as carrot roots and tobacco leaves.