Cyanogenic Glycosides in Plant Defense Mechanisms

Cyanogenic glycosides (CGs) constitute a widespread two-component defence system in higher plants, coupling a non-toxic glucosylated α-hydroxynitrile with one or more hydrolytic enzymes in separate cellular compartments. Upon tissue damage, β-glucosidases cleave the sugar moiety to liberate hydrogen cyanide (HCN) alongside deterrent aldehydes or ketones, rapidly inhibiting herbivores and pathogens by blocking cytochrome c oxidase in their respiratory chains. Structurally diverse CGs, derived from amino acids such as tyrosine, valine and isoleucine, have arisen independently multiple times across angiosperm lineages in a process of convergent metabolic evolution. Biosynthesis typically involves cytochrome P450 monooxygenases and UDP-glycosyltransferases, which often reside in co-expressed genomic clusters to ensure coordinated flux and to protect the plant from self-poisoning via vacuolar sequestration or specialised transporters. Beyond direct toxicity, CGs can function as temporary nitrogen reserves and may contribute to induced systemic resistance, interpopulation signalling and modulation of herbivore behaviour. The fine-tuned balance between synthesis, storage, activation and turnover underpins both ecological interactions and the potential for crop improvement through biotechnological manipulation of CG pathways.

Research from Nature Portfolio

Recent studies on the sorghum CG dhurrin have uncovered a co-expressed multidrug and toxic compound extrusion (MATE) transporter within its biosynthetic gene cluster. This transporter localises to the vacuolar membrane and actively shuttles dhurrin into the vacuole, thereby preventing cytosolic self-toxicity and streamlining defence metabolite storage. Functional expression assays in heterologous oocyte systems confirmed broad specificity for dhurrin and related CGs, shedding light on how coordinated gene clustering and transport mechanisms have evolved to optimise both synthesis and safe compartmentalisation of potent defence compounds.

Cyanogenic Glycosides in Plant Defense Mechanisms publication trend

The graph below shows the total number of articles in cyanogenic glycosides in plant defense mechanisms across all publications each year (not limited to Nature Index journals).

Technical terms

Cyanogenic glycoside: A glucosylated α-hydroxynitrile that releases hydrogen cyanide upon enzymatic hydrolysis as a plant defence compound.

β-Glucosidase: An enzyme that cleaves the glucose moiety from cyanogenic glycosides, triggering cyanide release.

MATE transporter: A multidrug and toxic compound extrusion protein that facilitates vacuolar sequestration of defence metabolites such as dhurrin.

Glutathione transferase (GST): An enzyme that catalyses conjugation of glutathione to metabolites, here involved in recycling of cyanogenic glucosides without cyanide liberation.

Nitrilase: An enzyme that hydrolyses nitrile intermediates to carboxylic acids and ammonia, completing the turnover of recycled cyanogenic compounds.

References

1. The case for sporadic cyanogenic glycoside evolution in plants. Current Opinion in Plant Biology (2024).
2. The biosynthetic gene cluster for the cyanogenic glucoside dhurrin in Sorghum bicolor contains its co-expressed vacuolar MATE transporter. Scientific Reports (2016).
3. Glutathione transferases catalyze recycling of auto‐toxic cyanogenic glucosides in sorghum. The Plant Journal (2018).