SAMPLE ABSTRACT FORMAT:

Cyanogenic Glycoside Transport in Cassava: Implications for the Generation of a Cyanogen-Free Cassava Plant

Dimuth Siritunga and Richard T. Sayre

Department of Plant Biology, 318 W. 12th Ave., Ohio State University, Columbus, OH 43210 USA. (Siritunga.1@osu.edu)

The evidence for long-distance transport of cyanogenic glucosides in plants is not well documented although it has been demonstrated that cyanogenic glycosides are transported during early stages of development in sorghum and rubber tree. Here, we present evidence in support of the long-distance transport of cyanogenic glucosides in cassava. Cassava accumulates potentially toxic levels of cyanogenic glycosides (linamarin, 95% and lotaustralin 5%) in all parts of the plant. The first dedicated step in linamarin synthesis is catalyzed by two similar cytochrome P450s encoded by the CYP79D1 and CYP79D2 genes. Using tissue-specific promoters to drive the expression of CYP79D1/D2 antisense constructs, we have successfully generated transgenic cassava plants in which the steady-state levels of the CYP79D1 and CYP79D2 transcripts have been selectively reduced or eliminated in leaves and roots. Importantly, root linamarin content was unaltered in transformants in which CYP79D1/D2 transcripts steady-state levels were reduced to non-detectable levels in roots. In contrast, the root linamarin content of transformants having substantially reduced CYP79D1/D2 transcripts levels in leaves was reduced by 99%. These results suggest that linamarin made in the leaves is transported to the roots. Further analysis of the growth of transgenic cassava in media lacking ammonia suggests that cyanogenic glucosides may function as an important mobile nitrogen source in young plants in addition to their proven ability to deter herbivory.