ODORANT1 targets multiple metabolic networks in petunia flowers.

Scent bouquets produced by petunia flowers are composed of a complex mixture of floral volatile benzenoid and phenylpropanoid compounds (FVBPs), which are specialized metabolites derived from phenylalanine (Phe) through an interconnected network of enzymes. Biosynthesis and emission of high levels of these volatiles requires coordinated transcriptional activation of both primary and specialized metabolic networks. The petunia R2R3-MYB transcription factor ODORANT1 (ODO1) was identified as a master regulator of FVBP production and emission; however, knowledge of direct regulatory targets of ODO1 has remained limited. Using ChIP-seq in petunia flowers, we identify ODO1-bound genes genome-wide, which are enriched not only in genes involved in the biosynthesis of Phe precursor as previously reported, but also genes in the specialized metabolic pathways involved in generating phenylpropanoid intermediates for FVBPs. ODO1-bound genes are also involved in methionine and S-adenosylmethionine metabolism, which could modulate methyl group supplies for certain FVBPs. qRT-PCR and RNA-seq analysis in an ODO1 RNAi knockdown line revealed that ODO1-bound targets are expressed at lower levels when ODO1 is suppressed. A cis-regulatory motif, CACCAACCCC, was identified in the promoters of genes that are both bound and activated by ODO1 as a potential binding site for ODO1, which was validated by in planta promoter reporter assays with wild-type and mutated promoters. Overall, our work presents a mechanistic model for ODO1 controlling an extensive gene regulatory network that contributes to FVBP production to give rise to floral scent.