Regulation of floral volatile synthesis in Petunia x hybrida CV 'Mitchell diploid'

Floral volatile emission comprises a unique blend of volatile compounds divergent among species of angiosperms. These volatiles have been proposed to function in a variety of physiological processes, including pollinator attraction and plant defense against fungal and bacterial pathogens as well as herbivores. Biosynthesis of floral volatiles is a tightly regulated process dependent on many factors including time of day, developmental stage of the flower, pollination status, and wounding. In this study, two genes from Petunia x hybrida cv "Mitchell Diploid" (MD), benzoyl-CoA: benzyl alcohol/phenyl ethanol benzoyltransferase (PhBPBT) and acetyl-CoA: coniferyl alcohol acetyltransferase (PhCFAT), were identified and shown (via RNAi-induced gene silencing) to be critical to floral volatile biosynthesis in petunia. In PhBPBT RNAi transgenic petunia lines, benzyl benzoate emission decreased >90%, while emission of benzyl alcohol and benzaldehyde increased when compared to MD. In PhCFAT RNAi transgenic petunia lines, isoeugenol emission decreased >90%, with lower levels of several other volatiles also observed.; To better define the transcriptional regulation of floral volatile biosynthesis genes, PhBPBT and PhCFAT transcript levels were quantified. Transcript levels from both genes were primarily expressed in the petal limb, were rhythmically expressed dependent on the time of day, and underwent developmental regulation with highest levels observed during anthesis. Utilizing 44568 (35S CaMV:etr1-1) transgenic petunias, effects of pollination and wound-induced ethylene were also identified. In the corolla, pollination-induced ethylene decreased transcript levels of both genes. However, in the ovary tissue, ethylene sensing was associated with an increase in PhBPBT transcript. Additionally, an increase in PhBPBT transcript was also observed in vegetative tissue following mechanical wounding. Further insight into the effects of environmental stimuli (light and temperature) on volatile emission, and physiological interactions with pollinator, fungal pathogens, and humans were also addressed. Improved understanding of the complex regulation of floral volatile biosynthesis will allow more effective engineering of floral volatile emission.