Folate is a B-group vitamin critical for normal cellular function and division. It acts in one-carbon transfer systems essential in nucleotide synthesis, methylation and gene expression. Insufficient intake causes megaloblastic anaemia and there are strong linkages to cardiovascular disease, various cancers and cognitive decline. Low levels prenatally can lead to low birth weight and premature infants and catastrophic neural tube defects including spina bifida and anencephaly.
Vertebrates are unable to synthesize folate de novo, accordingly plant foods are the primary source. Cereals unfortunately, which provide over half the worlds population with 80% of their diets are particularly poor in folate. Consequently the majority of the worlds developed nations have fortification programmes. In the developing world however, such programmes are logistically far more difficult. A viable alternative is metabolic engineering, the ultimate aim being creation of a crop plant producing high folate levels.
Folate is produced in a multi-step process from a pterin ring, p-aminobenzoate (pABA) and glutamate residues. Earlier attempts to engineer elevated folate in plants focused on enhancing pterin which produced moderately higher levels of folate. Crossing of such plants with those engineered to express genes of the pABA pathway resulted in significant level of folate in fruit, however in these cases genes from other Orders were introduced. Here we show rice plants transgenic for wheat 7,8-dihydropteroate synthase (DHPS) which operates at a central point in the production pathway, gives elevated folate levels. Consequently we have a cereal crop transgenic for a single cereal gene expressing enhanced folate levels.