Benzaldedyde, commonly detected in plant VOC (volatile organic compounds) profiling, is derived from phenylalanine. However, the last enzymatic step for benzaldedyde formation, designated as benzaldehyde synthase, remains elusive for long time. Here, we demonstrated that cinnamoyl-CoA reductases are responsible for benzaldedyde production in cucumber (Cucumis sativus L.). Comprehensive tissue specificity of VOC profiling revealed that benzaldehyde was specifically accumulated in root and flower of cucumber plants. VOC-gene correlation analysis suggested that several CCRs are candidate genes for benzaldehyde production: CsaCCR7 had a root-specific expression pattern while CsaCCR9 and CsaCCR18 showed a flower-specific expression pattern. Enzymatic assay demonstrated that CsaCCR7, CsaCCR9 and CsaCCR18 convert benzoyl-CoA to benzaldehyde. Subcellular localization experiments revealed that CsaCCR7 and CsaCCR18 are localized in cytosol, while CsaCCR9 was localized in peroxisome. In contrast to the long-standing view that CCR enzymes are involved in lignin biosynthesis in plants, it is the first time here to add a new biochemical role of CCR as benzaldehyde synthase in plants.

Benzaldehyde Synthases Are Encoded by Cinnamoyl-CoA Reductase Genes in Cucumber (Cucumis sativus L.)