Generation of cyanogen-free transgenic cassava

Abstract

Cassava (Manihot esculenta Crantz.) is the major source of calories for subsistence farmers in sub-Saharan Africa. Cassava, however, contains potentially toxic levels of the cyanogenic glucoside, linamarin. The cyanogen content of cassava foods can be reduced to safe levels by maceration, soaking, rinsing and baking; however, short-cut processing techniques can yield toxic food products. Our objective was to eliminate cyanogens from cassava so as to eliminate the need for food processing. To achieve this goal we generated transgenic acyanogenic cassava plants in which the expression of the cytochrome P450 genes (CYP79D1 and CYP79D2), that catalyze the first-dedicated step in linamarin synthesis, was inhibited. Using a leaf-specific promoter to drive the antisense expression of the CYP79D1/CYP79D2 genes we observed up to a 94% reduction in leaf linamarin content associated with an inhibition of CYP79D1 and CYP79D2 expression. Importantly, the linamarin content of roots also was reduced by 99% in transgenic plants having between 60 and 94% reduction in leaf linamarin content. Analysis of CYP79D1/CYP79D2 transcript levels in transgenic roots indicated they were unchanged relative to wild-type plants. These results suggest that linamarin is transported from leaves to roots and that a threshold level of leaf linamarin production is required for transport.

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Acknowledgements

Special thanks to Dr. Johnnie Brown of the Ohio State University, Campus Chemical Instrument Center for GC–MS method development for linamarin quantification and Dr. J.C. Jang of the Ohio State University, Horticulture and Crop Science department for critical comments on this manuscript. This research has been supported by grants from the Rockefeller Foundation, the Consortium for Plant Biotechnology Research, the Cassava Biotechnology Network, and the Ohio State University (to R.T.S.). This paper is dedicated to Dr. Chusa Ginés and Verónica Mera.

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Correspondence to Richard T. Sayre.

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Siritunga, D., Sayre, R.T. Generation of cyanogen-free transgenic cassava. Planta 217, 367–373 (2003). https://doi.org/10.1007/s00425-003-1005-8

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Keywords

  • Manihot
  • Cyanogenic glycoside
  • Cyanide
  • Linamarin
  • Cytochrome P450