Metabolic Engineering of Ketocarotenoid Production in Carrot

Ketocarotenoids are a group of naturally occurring pigments synthesized by a number of algae and cyanobacteria. They have been reported to stimulate immune functions, exhibit anti-bacterial properties, prevent tissue damage by ultraviolet light and reduce oral cancer and mammary tumor growth in animal models. Ketocarotenoids, such as astaxanthin and canthaxanthin, have been regarded as important dietary supplements because of their strong antioxidant properties, even surpassing those of lycopene and β-carotene. They are also added to the feed of farmed salmons and crustaceans to achieve adequate growth and reproduction and as a flesh colorant. However, the derivation of astaxanthin by chemical synthesis is currently hindered by  the presence of contaminating reagents and reaction intermediates. Large scale production of these compounds from alga and microorganisms has also proven to be inconvenient because of their slow growth and special growth conditions.  

A group of scientists has successfully demonstrated the use of metabolic engineering in producing ketocarotenoid from carrots. Previous efforts to develop transgenic tomato, potato and tobacco plants with high ketocarotenoids levels did not yield lines with sufficient levels for industrial applications. By introducing a gene from the algae Haematococcus pluvialis coding for an enzyme necessary for the compound’s biosynthesis, they were able to produce GM carrots expressing very high ketocarotenoid levels. One advantage of using carrots over other crops is the presence of high levels of α and β-carotene in the roots, which are converted to novel ketocarotenoids. They reported up to 70% total carotenoid to ketacarotenoid conversion, with astaxanthin, adonirubin, and canthaxanthin being the most prevalent. Their results show that carrots are suitable for biopharming ketocarotenoids for applications for the functional food, neutraceutical and aquaculture industries.

The original paper published by the  journal Transgenic Research is available to subscribers at http://www.springerlink.com/content/9748573704211740/fulltext.html