Science is changing the world at an exponential rate. We can send robots to planets, store millions of pages of information in our pockets, and transplant faces from one person to another. We can analyze the DNA blueprint of all life, and now, we are able to modify it. This power comes with a lot of ethical questions, which is why most major genome modifications today have happened in plants. The best example of this is golden rice. By inserting three genes into the rice’s DNA, the rice starts to naturally produce beta-carotene giving the rice its characteristic golden color. Here is a brief explanation of the science behind it.
Rice already makes beta-carotene in the leaves, so the general mechanism already exists in the DNA. Some parts of the pathway are disabled in the endosperm (part of the rice plant that is eaten). Rice endosperm synthesizes geranylgeranyl diphosphate (GGPP), a precursor for carotenoids. Before the advent of golden rice, it was thought that six enzymes were needed to turn GGPP into beta-carotene. This is true in plants; however, bacteria take a shorter route. Plants use four enzymes to convert GGPP to lycopene, a closer precursor to beta-carotene. Bacteria uses two enzymes (PSY and CRTI) to convert GGPP produce lycopene. After this, both plants and bacteria use atwo similar enzymes to convert lycopene into beta-carotene.
In 2000, scientists discovered that adding a PSY gene and CRTI gene to the endosperm triggered the accumulation of beta-carotene in the endosperm of the rice. The plant has its own PSY gene, but it is inactive in the endosperm. The two genes were introduced into the genome using a plasmid and Agrobacterium. Plasmids are bacterial DNA looped into a circle. Agrobacterium is a group of bacteria that can insert DNA from its plasmids into plant genomes. Genes are converted to proteins by the plant’s molecular machinery. Agrobacterium inserts its genome into plant cells so that the plant’s molecular machinery makes Agrobacterium protein effectively, turning a plant cell into the bacteria’s personal factory.
Scientists can take advantage of this phenomenon and insert any gene they want into plants by way of the plasmid. Enzymes that cut and repair plasmid DNA are used to achieve this. The plasmid also has a set of genes known as virulence genes. They activate upon sensing acetosyringone, a molecule produced by damaged plant cells. This is important, as the bacteria can only insert plasmid DNA through damaged plant cells. The activated virulence genes ultimately produce virulence proteins, which are responsible for cleaving off the DNA from the plasmid and inserting it into the plant genome.
What is the purpose of producing beta-carotene in rice? Golden rice seeks to serve people in third world countries who do not receive enough Vitamin A. Vitamin A deficiency causes 1-2 million deaths and 500,000 cases of blindness per year. With the most recent version, only 75 grams of golden rice are needed to provide sufficient Vitamin A intake. The only obstacle that golden rice does not solve is that people must also have sufficient fat intake to use Vitamin A properly in the body. Finding sufficient fat sources in developing country is still a hurdle that golden rice must leap over. Genetically modifying crop is still in its early stages of development. As time goes on, golden rice may dramatically improve to overcome the problem of fat intake, and genetic modifying techniques may be used to improve nutrition in other crops.
