Floral fragrance production is a specialized process.

摘要

Floral fragrance is an integral factor for many angiosperm species interacting with an environment. Individual fragrant flowering species emit specific mixtures and combinations of volatile organic compounds, which can function in various aspects of plant biology. Petunia x hybrida cv "Mitchell Diploid" (MD) has large white flowers that emit floral volatile benzenoid/phenylpropanoid (FVBP) compounds in a controlled manner. FVBP emission is confined to the corolla limb tissue, from anthesis to senescence, in a rhythmic pattern where peak FVBP emission is nocturnal. The object of this study was to investigate molecular, biochemical, and metabolic aspects of regulation committed to FVBP production in petunia. Therefore, seven MD genes previously identified as necessary for differential aspects of FVBP production were assayed for coordinate transcriptional regulation. The transcript accumulation assay resulted in similar transcript accumulation profiles for all FVBP genes examined in three out of four categories. Together with previous characterizations, these results indicate that the FVBP genes are a part of a specific group, which is involved in a specific enterprise. Utilizing the transcript accumulation screen and focusing further research on candidate genes whose transcript profiles were similar to known FVBP profiles, PhCM1 and PhMYB5d8 were identified. PhCM1 encodes a plastid localized CHORISMATE MUTASE (CM) isoform that catalyzes the initial committed 11 step in phenylalanine biosynthesis and is the major CM isoform involved in FVBP production. While characterizing PhCM1, PhCM2 was identified as a cytosolic CM isoform, but the transcript accumulation profile was not consistent with FVBP gene profiles and the cytosolic localization separated PhCM2 from pathway proteins and metabolites. Lastly, PhMYB5d8 encodes an R2R3-MYB transcriptional regulator that contains a C-terminal EAR-domain. A reverse genetic approach suggests that PhMYB5d8 negatively regulates CINNAMATE-4-HYDROXYLASE transcript accumulation in the corollas of open petunia flowers.;In short, a simple and cost-effective molecular screen was designed to assay candidate genes for a possible involvement in FVBP production. Two genes were identified and empirically shown to be involved in FVBP production. That is, a biosynthetic enzyme which directs metabolite flux to phenylalanine production and a transcriptional regulator managing transcript levels of a biosynthetic enzyme "downstream" of phenylalanine.