Deciphering phenylalanine-derived salicylic acid biosynthesis in plants.

Salicylic acid (SA) is a ubiquitous plant hormone with a long history in human civilization(1,2). Because of the central role of SA in orchestrating plant pathogen defence, understanding SA biosynthesis is fundamental to plant immunity research and crop improvement. Isochorismate-derived SA biosynthesis has been well defined in Arabidopsis. However, increasing evidence suggests a crucial function for phenylalanine-derived SA biosynthesis in many other plant species(1). Here we reveal the phenylalanine-derived SA biosynthetic pathway in rice by identifying three dedicated enzymes - peroxisomal benzoyl-CoA:benzyl alcohol benzoyltransferase (BEBT), the endoplasmic reticulum-associated cytochrome P450 enzyme benzylbenzoate hydroxylase (BBH), and cytosolic benzylsalicylate esterase (BSE) that sequentially convert benzoyl-CoA to benzylbenzoate, benzylsalicylate and SA. The pathogen-induced gene expression pattern and SA biosynthetic functions of this triple-enzyme module are conserved in diverse plants. This work fills a major knowledge gap in the biosynthesis of a key plant defence hormone, establishing a foundation for new strategies to create disease-resistant crops.