In 1996 the World Food Summit stated that ‘food security exists when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life’. Currently, just 17 plant species are consumed as 90% of the global human diet, meaning that many lack adequate vitamins, micro-nutrients and health-promoting phytonutrients. Vitamin D is synthesised by humans from dehydrocholesterol, following exposure to sunlight, but the major source is dietary. Pro-vitamin D3 (7-dehydrocholesterol; 7-DHC) is synthesised by some plants, on route to cholesterol synthesis. By editing the gene encoding the steroidal glycoalkaloid-specific isoform of the enzyme synthesising cholesterol from 7-DHC, we have been able to increase the levels of 7-DHC in tomato fruit such that they approach the values for the RDA for vitamin D.
Vitamin C (ascorbate) plays a vital role in stress tolerance and amelioration of oxidative stress in both plants and animals. Ascorbate is also important in iron uptake by plants and mammals. Multiple ascorbate biosynthetic pathways have been proposed in plants but there is now consensus that GDP-L-galactose phosphorylase (GGP) is the first committed and rate-limiting enzyme of the L-galactose pathway and GGP activity is controlled by negative feedback regulation of its translation. Genome edits that remove or reduce this negative regulation result in increased levels of ascorbate. Genome editing can make a major contribution to fortifying foods popular with consumers so that all can enjoy a healthier diet.