Three-step biosynthesis of salicylic acid from benzoyl-CoA in plants.

Salicylic acid (SA) is the active ingredient in willow bark that has been used for anti-inflammation and pain relief for centuries. Aspirin, a derivative of SA, is the most widely used medication in human history. SA also acts as a key plant defence hormone. Although SA was known to be produced from chorismate in the model plant Arabidopsis, how it is biosynthesized in plant families outside Brassicaceae remains unclear. Here we report the identification of a conserved pathway for SA biosynthesis in seed plants. Using Nicotiana benthamiana as a model, we identified three key steps for the biosynthesis of SA. First, ligation of benzoyl coenzyme A (CoA) and benzyl alcohol by benzoyl-CoA:benzyl alcohol benzoyl transferase (BEBT) gives rise to benzyl benzoate, which is then hydroxylated by benzyl benzoate oxidase (BBO) to produce benzyl salicylate. Subsequent cleavage of benzyl salicylate by benzyl salicylate hydrolase (BSH) yields SA. Notably, genes encoding these three enzymes are present in a broad range of plants, and the genes from dicots such as willow, poplar and soybean as well as the monocot rice can complement the phenotype of SA-deficient mutants of N. benthamiana. Moreover, knockout analysis of the Oryza sativa OsBEBT, OsBBO and OsBSH genes reveals that they are required for SA biosynthesis in rice. Our findings suggest that the SA biosynthesis pathway is highly conserved in plants.