Herbivore-induced phenylacetonitrile is biosynthesized from de novo-synthesized l-phenylalanine in the giant knotweed, Fallopia sachalinensis

• The biosynthetic origin of herbivore-induced plant nitrile was examined.
• Herbivore-induced phenylacetonitrile is biosynthesized from l-phenylalanine.
• l-Phenylalanine biosynthesis is induced by herbivory or exogenous methyl jasmonate.
• Methyl jasmonate activates both the shikimate pathway and the nitrile biosynthetic pathway.
• Exogenous methyl jasmonate enhances biosynthesis of several amino acids in planta.

Plants emit a series of characteristic volatile blends when damaged by insect feeding. Phenylacetonitrile is one of the volatiles from the leaves of the giant knotweed, Fallopia sachalinensis, infested by the Japanese beetle, Popillia japonica, or treated with exogenous airborne methyl jasmonate (MeJA). We examined the precursor of the nitrile and its origin in this system. l-Phenylalanine was determined to be a precursor of the nitrile in F. sachalinensis leaves, and the phenylalanine was also induced by beetle feeding and MeJA treatment. We also found that exogenous MeJA enhanced the biosynthesis of several amino acids in F. sachalinensis leaves.