Plant Biochemistry Laboratory, Department of Plant Biology and Biotechnology, University of Copenhagen, and VKR research centre “Pro-Active Plants”
Cyanogenic glucosides are widely distributed natural products in the plant kingdom and are also present in cassava. Plants contain degradative enzymes that upon cellular disruption of the plant tissue are brought in contact with the cyanogenic glucosides causing hydrogen cyanide release. This binary system - two sets of components which separately are chemically inert – provides cyanogenic plants with an immediate chemical defence response to herbivores and pathogens causing tissue damage. Our lab has pioneered the isolation of the four genes encoding the entire pathway for linamarin and lotaustralin biosynthesis in cassava. We have now discovered that cyanogenic glucosides may also be turned-over by an endogenous pathway resulting in the release of ammonia without release of hydrogen cyanide. In this way, cyanogenic glucosides serve to balance nitrogen supply to developing tissues. The endogenous pathway involves glucosidases, glucosidase modifying factors and heteromeric nitrilase complexes. Different heteromers of the nitrilases have different substrate specificities and enable the plant to use combinatorial biochemistry to control the endogenous turn-over of cyanogenic glucosides without release of hydrogen cyanide. A molecular understanding of this metabolic grid provides a unique opportunity to re-direct and channel nitrogen from cyanogenic glucosides into protein synthesis. The trait of cyanogenesis is about 430 million years old and has enabled co-evolution of cyanogenic plants and their herbivores and pests as well as the recruitment of new functions of cyanogenic glucosides in primary metabolism in plants and insects.