Benzyl alcohol biosynthesis and its subcellular compartmentalization enable scent formation and salicylic acid...

Benzyl alcohol, a simple aromatic alcohol found in more than half of seed plant families, plays important roles in plant-environmental interactions and serves as a precursor of benzyl benzoate, an intermediate in the phenylalanine-dependent biosynthesis of the phytohormone salicylic acid. Despite its importance, the enzyme responsible for benzyl alcohol formation in plants has remained unknown. Using a combination of classical biochemical, proteomic and genetic approaches, we demonstrated that two NADPH-dependent benzaldehyde reductases, differing by only three amino acids, are responsible for the formation of benzyl alcohol and its downstream derivatives, benzyl benzoate and methyl salicylate, in petunia flowers. Moreover, downregulation of benzaldehyde reductase expression substantially reduces salicylic acid levels in petunia stems upon pathogen infection. These findings provide direct evidence that benzaldehyde reductase is the last unidentified enzyme in salicylic acid biosynthesis via the benzyl benzoate intermediate. Moreover, the subcellular localization of benzaldehyde reductase homologs across flowering plants is species-specific, occurring either in peroxisomes or cytosol, suggesting that different species employ distinct compartmental organization for phenylalanine-dependent salicylic acid biosynthesis.