Diversification of an ancient theme: hydroxynitrile glucosides

Area of Science:

• Plant biochemistry
• Natural product chemistry
• Plant defense mechanisms

Background:

• Cyanogenic glucosides (alpha-hydroxynitrile glucosides) are common plant defense compounds releasing toxic hydrogen cyanide (HCN).
• Beta- and gamma-hydroxynitrile glucosides are less understood compounds that do not release HCN upon hydrolysis.
• Their biosynthesis and biological roles remain largely unknown.

Purpose of the Study:

• To identify and characterize novel beta-hydroxynitrile glucosides from Ribes uva-crispa.
• To investigate the co-occurrence and biosynthetic origins of beta- and gamma-hydroxynitrile glucosides in various plant species.
• To determine the genetic basis for the presence of these glucosides in Lotus japonicus.

Main Methods:

• Isolation and structural elucidation of beta-hydroxynitrile glucosides from R. uva-crispa.
• Analysis of hydroxynitrile glucoside profiles in Ribes, Rhodiola, and Lotus species.
• Radiolabelling experiments using L-isoleucine and L-leucine.
• Metabolite profiling, genetic crosses, and F2 population analysis in Lotus japonicus.

Main Results:

• Three novel beta-hydroxynitrile glucosides were isolated from R. uva-crispa.
• Beta- and gamma-hydroxynitrile glucosides were found to co-occur with known cyanogenic glucosides in several plant genera.
• Radiolabelling confirmed L-isoleucine and L-leucine as precursors for hydroxynitrile glucosides in R. uva-crispa and Hordeum vulgare, respectively.
• A single recessive genetic trait was identified as responsible for the presence/absence of beta- and gamma-hydroxynitrile glucosides in L. japonicus.

Conclusions:

• Beta- and gamma-hydroxynitrile glucosides are novel plant natural products with distinct structures and properties.
• These compounds are derived from common amino acids and likely represent a diversification of the cyanogenic glucoside biosynthetic pathway.
• Genetic factors play a significant role in the production of these glucosides in plants.