Abstract
Benzaldehyde, the simplest aromatic aldehyde, is one of the most wide-spread volatiles that serves as a pollinator attractant, flavor, and antifungal compound. However, the enzyme responsible for its formation in plants remains unknown. Using a combination of in vivo stable isotope labeling, classical biochemical, proteomics and genetic approaches, we show that in petunia benzaldehyde is synthesized via the β-oxidative pathway in peroxisomes by a heterodimeric enzyme consisting of α and β subunits, which belong to the NAD(P)-binding Rossmann-fold superfamily. Both subunits are alone catalytically inactive but, when mixed in equal amounts, form an active enzyme, which exhibits strict substrate specificity towards benzoyl-CoA and uses NADPH as a cofactor. Alpha subunits can form functional heterodimers with phylogenetically distant β subunits, but not all β subunits partner with α subunits, at least in Arabidopsis. Analysis of spatial, developmental and rhythmic expression of genes encoding α and β subunits revealed that expression of the gene for the α subunit likely plays a key role in regulating benzaldehyde biosynthesis.
Highlights
Benzaldehyde, the simplest aromatic aldehyde, is one of the most wide-spread volatiles that serves as a pollinator attractant, flavor, and antifungal compound
By combining in vivo stable isotope labeling with classical biochemical, proteomics and genetic approaches, we found that benzaldehyde is synthesized via the β-oxidative pathway and a heterodimeric enzyme consisting of α and β subunits, both of which belong to NAD(P)
Pseudomonas putida, benzaldehyde is an intermediate in the mandelic acid degradation pathway[52], while in Nocardia iowensis, it is formed by a carboxylic acid reductase (CAR), a large multidomain enzyme, which first produces benzoyl-AMP from benzoic acid and ATP followed by its reduction to benzaldehyde with NADPH as a cofactor[53]
Summary
Benzaldehyde, the simplest aromatic aldehyde, is one of the most wide-spread volatiles that serves as a pollinator attractant, flavor, and antifungal compound. Using a combination of in vivo stable isotope labeling, classical biochemical, proteomics and genetic approaches, we show that in petunia benzaldehyde is synthesized via the β-oxidative pathway in peroxisomes by a heterodimeric enzyme consisting of α and β subunits, which belong to the NAD(P)-binding Rossmann-fold superfamily. 1234567890():,; Benzaldehyde is the simplest aromatic aldehyde found in nature, consisting of a single benzene ring bearing an aldehyde group It is one of the most widely distributed volatiles and is likely the most ancient compound given that it is produced by over 50% of plant families analyzed so far for their volatile profiles[1], and by insects and non-insect arthropods[2]. Enzyme activity catalyzing similar non-oxidative formation of benzaldehyde from cinnamic
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