Poster: Metabolic Engineering
Abs #
1000: Cyanogenic-glucosides are a mobile source of reduced nitrogen in cassava
Cyanogenic glucosides and glucosinolates share a common first step in their synthesis; an aldoxime that is derived from the mono-oxygenation of an amino acid. Long-distance transport of glucosinolates in the phloem is well documented in several plant species. The evidence for long-distance transport of cyanogenic glucosides, however, is less 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 reduced nitrogen as cyanogenic glucosides in cassava, one of the most agronomically important crops in the tropics. We have successfully generated transgenic cassava plants in which the steady-state levels of the CYP79D1 and CYP79D2 transcripts (responsible for the conversion of valine to its aldoxime) have been selectively inhibited in leaves or roots. Using GC-MS, the leaf and root linamarin content were measured. The leaf and root linamarin content was unaltered in transformants in which CYP79D1/D2 transcripts steady-state levels were selectively reduced to non-detectable levels in roots. In comparison, the leaf linamarin content of transformants having substantially reduced CYP79D1/D2 transcripts levels in leaves was reduced by as much as 94%. The same transformants also exhibited a substantial reduction in root linamarin content, down to 1% of wild-type levels. These results suggest that linamarin made in the leaves is transported to the roots. Further analysis on the growth of transgenic cassava in media containing +/- ammonia suggests that cyanogenic glucosides apparently function as an important mobile nitrogen source, in addition to their proven ability to deter herbivory.
