A team led by Zhang Jian at the National Key Laboratory of Paddy Rice Biological Breeding of the China Rice Research Institute, has increased the oil content of rice seeds from 2.3% to 11.7% using synthetic biology methods. This has brought a new technological approach to the conversion of high-yield starch food crops such as rice, maize, potato, and cassava into oilseeds.
Soybeans have an oil content of 15-26% and a protein content of about 40%, with a production of about 2 tons per hectare. Food crops such as rice and potatoes are more productive, but have somewhat lower oil and protein content. For example, rice has an oil content of 2-3% and a protein content of about 10%, with a production per hectare of about 2 tons.
Zhang used a promoter specific to rice endosperm to express a restricted gene for Arabidopsis oil synthesis in the endosperm, thereby increasing the efficiency of oil synthesis in the seed. Next, they used genome editing technology to knock down key genes that synthesize starch in rice, blocking part of the starch synthesis route and drawing carbon sources into the oil and fat synthesis route. Then they knocked down a gene that negatively regulates the aleurone layer of rice, increasing the thickness of the aleurone layer of rice, the oil storage tissue, and expanding the capacity of oil and fat in rice seeds. Finally, they produced rice genetics with a high oil content in the major rice cultivar “Nanluo46” in the rice production area of southern China. The relative oil content of brown rice increased from 2.33% to 11.72%, the highest level ever reported for a starch food crop and on par with oilseed crops such as soybeans.