Transgenic Biofortification of the Starchy Staple Cassava (Manihot esculenta) Generates a Novel Sink for Protein

Although calorie dense, the starchy, tuberous roots of cassava provide the lowest sources of dietary protein within the major staple food crops (Manihot esculenta Crantz). (Montagnac JA, Davis CR, Tanumihardjo SA. (2009) Compr Rev Food Sci Food Saf 8:181-194). Cassava was genetically modified to express zeolin, a nutritionally balanced storage protein under control of the patatin promoter. Transgenic plants accumulated zeolin within de novo protein bodies localized within the root storage tissues, resulting in total protein levels of 12.5% dry weight within this tissue, a fourfold increase compared to non-transgenic controls. No significant differences were seen for morphological or agronomic characteristics of transgenic and wild type plants in the greenhouse and field trials, but relative to controls, levels of cyanogenic compounds were reduced by up to 55% in both leaf and root tissues of transgenic plants. Data described here represent a proof of concept towards the potential transformation of cassava from a starchy staple, devoid of storage protein, to one capable of supplying inexpensive, plant-based proteins for food, feed and industrial applications.