Genetically Modified Rice Stacked With Antioxidants

Chinese researchers have developed a genetic engineering tool to generate antioxidant-rich purple rice.

AsianScientist (July 17, 2017) – Researchers in China have developed a genetic engineering approach to make purple rice that produces high levels of antioxidants. Their work is published in the journal Molecular Plant.

Rice is a staple food in Asia, making it a good agent for delivering micronutrients that are beneficial to health. However, not all micronutrients are produced in large quantities by rice.

To date, genetic engineering approaches have been used to develop rice enriched in beta-carotene and folate (precursors of vitamins A and B), but not anthocyanins. Anthocyanins are natural antioxidants that have the potential to decrease the risk of certain cancers, cardiovascular disease, diabetes, and other chronic disorders.

Although these health-promoting compounds are naturally abundant in some black and red rice varieties, they are absent in polished rice grains because the husk, bran and germ have been removed, leaving only the endosperm—the fleshy part at the center of the grain.

In this study, researchers developed a method to deliver many genes at once and used it to make rice endosperm produce high levels of anthocyanins. Previous attempts to engineer anthocyanin production in rice have failed because the underlying biosynthesis pathway is highly complex and it has been difficult to efficiently transfer many genes into plants.

To address this challenge, Professor Liu Yao-Guang and his colleagues at the South China Agricultural University first set out to identify the genes required to engineer anthocyanin production in the rice endosperm. To do so, they analyzed sequences of anthocyanin pathway genes in different rice varieties and pinpointed the defective genes in japonica and indica subspecies that do not produce anthocyanins.

Based on this analysis, they developed a transgene stacking strategy for expressing eight anthocyanin pathway genes specifically in the endosperm of the japonica and indica rice varieties. The resulting purple endosperm rice had high anthocyanin levels and antioxidant activity in the endosperm.

“We have developed a highly efficient, easy-to-use transgene stacking system called TransGene Stacking II that enables the assembly of a large number of genes in single vectors for plant transformation,” said Liu. “This is the first demonstration of engineering such a complex metabolic pathway in plants. We envisage that this vector system will have many potential applications in this era of synthetic biology and metabolic engineering.”

In the future, this transgene stacking vector system could be used to develop plant bioreactors for the production of many other important nutrients and medicinal ingredients. The researchers plan to evaluate the safety of purple endosperm rice as biofortified food and they will also try to engineer the biosynthesis of anthocyanins in other crops to produce more purple endosperm cereals such as maize, wheat and barley.

The article can be found at: Zhu et al. (2017) Development of “Purple Endosperm Rice” by Engineering Anthocyanin Biosynthesis in the Endosperm with a High-Efficiency Transgene Stacking System.


Source: Cell Press; Photo: Zhu Qinlong.
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