Missing Link in Plant Vit C Pathway Discovered

Vitamin C (ascorbate) is an essential human nutrient, with important metabolic and antioxidant functions. Humans rely on dietary intake of vitamin C, mainly from fruits and vegetables, as our body is unable to synthesize this compound. Vitamin C deficiency is however a problem mainly in developing countries, especially Africa and southern Asia, where fresh fruits and vegetables are not always available, and access to vitamin supplements is limited.

A main pathway for the production of ascorbate in plants is the L-galactose pathway, and until recently, all the enzymes in this pathway except one had been identified. A team of scientists from New Zealand has now added the last piece to the puzzle, isolating a gene coding for the missing enzyme, an L-galactose guanyltransferase. The team also showed that over-expression of this gene results in a 3-fold increase in ascorbate in transgenic tobacco, indicating that the gene is likely to be the rate-limiting step for vitamin C production. This gene could therefore be used to manipulate crop plants for elevated vitamin C accumulation.

The open access article is published in this week's issue of the Proceedings of the National Academy of Sciences (PNAS), and can be viewed at http://www.pnas.org/cgi/reprint/104/22/9534