My family moved to San Francisco after I graduated from high school in China. My diet used to consist of my grandmother’s Chinese cooking. I am not picky about what I eat, so now I only have Chinese food when I go home. The staple food in a Chinese meal is rice, and it is commonly eaten as steamed rice. Rice is also a common material in many dishes. I want to discuss rice in this blog.
There are two species of rice plant, Oryza sativa and Oryza glaberrima. Oryza sativa is Asian rice, and Oryza glaberrima is African rice. The seeds, which grow at the top of rice plant, are collected and milled to get rid of the husks. Husks are rough coatings of the seeds. After this step, we have brown rice. To get white rice, the rest of husks and germ need to be removed. Rice can be cooked in water. The picture below is Oryza sativa, Asian rice.
White rice does not contain as much as nutrition as brown rice. For instance, in 100g white rice, there is 4.31g iron, 0g Vitamin A, and 0g of beta-carotene. Beta-carotene is a precursor of Vitamin A. Vitamin A deficiency can cause blindness. Iron deficiency can cause iron deficiency anemia, which can lead to morbidity and death. To address this problem, scientists have discovered methods to generically engineer rice so that it can contain additional vitamin and minerals.
Potrykus et al. at the Swiss Federal Institute of Technology Institute for Plant Sciences developed Golden Rice to address the Vitamin A and beta-carotene deficiency. They introduced a biosynthetic pathway of beta-carotene. The rice is transformed with phytoene synthase gene and phytoene desaturase gene, which are necessary for beta-carotene synthesis. These enzymes are expressed in rice endosperm. Beta-carotene will be converted into Vitamin A in animal intestines.
Left: regular rice. Right: golden rice. Beta-carotene has an organge color.
Potrykus et al. also developed iron-rich rice to prevent iron deficiency. A ferritin gene is transformed into rice to increase iron content. Ferritin is an iron storage protein. To decrease the iron absorption inhibitor, phytic acid, a thermo-tolerant phytase is also transformed into rice. Finally, they intend to increase the amount of cysteine peptides, which are iron absorption enhancer, by over-expressing a cysteine-rich protein. The iron rich rice contains higher amount of iron along with higher amount of iron absorption enhance and lower amount of iron absorption inhibitor.
Iron-rich rice in Potrykus lab.