The Golden Rice Project

    Golden Rice is a genetically modified strain of rice, which has been created by Prof. Ingo Potrykus, Prof. Peter Beyer and colleagues with the specific aim of reducing the prevalence of vitamin A deficiency.  The name 'Golden Rice' comes from the golden colour of the rice grains. 

    The symptoms of vitamin A deficiency (VAD) include night blindness, blindness, xerophthalmia, poor growth, increased mortality and increased vulnerability to infection. The effects are particularly bad in children and pregnant women.  According to World Health Organisation statistics, VAD causes 250000 - 500000 children to go blind every year. More than half of these die within a year of going blind.  The countries in which VAD is most severe are shown in this diagram:

    

        VAD is linked to diet.  The best way to obtain vitamin A is to eat a balanced diet including meat, which is rich in compounds called retinyl esters; the body can convert these to retinal - the form of vitamin A which is important for vision.   Plants contain compounds called carotenes, some of which can also be converted to retinal by the human body.  The most abundant is beta-carotene, which is also known as provitamin A. 

    In many of the countries where VAD is most severe (particularly India and countries in south east Asia), the staple food is rice.  In Cambodia, for example, rice accounts for 76% of human calories.  Although the rice plant does produce beta-carotene, it does not produce it in the endosperm - the part which we eat.  This is because the plants use beta-carotene for light capture in photosynthesis and this process does not occur in the endosperm. Therefore, it is not surprising that in many countries where a lot of rice and little meat is consumed, there are high levels of vitamin A deficiency. 

    This is where Golden Rice comes in.  Golden Rice has been genetically modified so that it does produce beta-carotene in the endosperm.

    The pathway by which beta-carotene is usually synthesised by plants (i.e. the pathway missing from rice endosperm) is shown below in a simplified form. The words in black are the names of the molecules and the words in red are the names of the enzymes that catalyse each step.

    In the rice endosperm, only one of these enzymes is present: lycopene cyclase. Therefore, the creators of Golden Rice took existing rice and added genes which code for enzymes to replace those not found in the endosperm.  They added two genes. The first is a gene from daffodil which codes for phytoene synthase. The second is a gene from a soil bacterium which codes for an enzyme called phytoene double-desaturase. This enzyme can catalyse both the second are third step in the pathway.  The genes were put under the control of an endosperm-specific promoter, so that the enzymes would be produced in the endosperm.  The pathway found in Golden Rice endosperm is shown below:

   The first version of Golden Rice contained an average of 6.6mg of provitamin A per gram of rice.  Some critics - particularly anti-GM campaigners - pointed out that large amounts of the rice would have to be eaten for a person to gain their full requirement of vitamin A (if the person was only eating rice).  In 2005, a new version of Golden Rice containing 32mg/g was produced.  This was named Golden Rice 2.  Although some beta-carotene is destroyed during cooking and not all of it is absorbed into the body, the level of beta-carotene in Golden Rice 2 is comfortably enough to prevent VAD in people eating ordinary amounts of rice.

    Beta-carotene is a pigment, which gives the golden rice grains their colour.  Photographs of normal rice, Golden Rice and Golden Rice 2 are shown below:

    There is no reason why Golden Rice should be dangerous or harmful to human health.  Firstly, beta-carotene is abundant in many foods of plant origin. For example, it gives carrots their orange colour.  Moreover, there is no reason why the two enzymes that have been added should be harmful to humans and even if they were, they are irreversibly destroyed by the cooking process. Nevertheless, Golden Rice had to be tested for safety in humans, as is sensible with all new foods.

To be completed...