Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2007
Publication Date: 2/5/2008
Citation: Dexter, R.J., Verdonk, J.C., Underwood, B.A., Shibuya, K., Schmelz, E.A., Clark, D.G. 2008. Tissue-specific PhBPBT expression is differentially regulated in response to endogenous ethylene. Journal of Experimental Botany. 59(3): 609-618. Interpretive Summary: Volatile chemicals produced by flowers and leaf tissues mediate complex interactions both internally within plants and also externally with other organisms. Many volatiles are believed to aid in plant resistance to insects and pathogens yet the precise role of specific chemicals is difficult to discern. To explore the function of individual volatiles, genes involved in either biosynthesis or regulation of the metabolic pathway can targeted for modification. In collaboration with researchers at the University of Florida, scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, have discovered that genetically silencing the gene responsible for floral benzyl benzoate synthesis, a known miticide, resulted in dramatically decreased benzyl benzoate production yet increased levels of metabolic precursors. Contrary to previous studies in petunia, plant morphology was not altered in the silenced lines. Using transgenic plants insensitive to the hormone ethylene, numerous pollination and wounding studies revealed patterns of gene expression and benzyl benzoate production that were consistent with a plant defense hypothesis. This work provides the genetic resources to examine the role of plant volatiles and highlights the importance of timing, localization, and tissue specificity as essential knowledge for examining function. Ultimately, these studies will lead to the beneficial modification of chemically mediated interactions between plants, pollinators, pathogens and pests.
Technical Abstract: Ethylene is a gaseous plant hormone involved in many physiological processes including senescence, fruit ripening, and defense. Here we show the effects of pollination and wound-induced ethylene signals on transcript accumulation of benzoyl CoA:benzyl alcohol/phenylethanol benzoyltransferase (PhBPBT), in Petunia x hybrida cv “MD Diploid” (MD). In petunia, PhBPBT is responsible for the biosynthesis of both benzyl benzoate and phenylethyl benzoate from benzyl alcohol and phenyl ethanol respectively. RNAi silenced lines, with reduced PhBPBT transcript, displayed reduced benzyl benzoate emission, and increased benzyl alcohol levels. Detailed expression analysis showed that PhBPBT is regulated by both light and an endogenous circadian rhythm, while it is also differentially regulated in response to ethylene in a tissue specific manner. Twenty-four h following pollination of MD flowers, expression of PhBPBT decreases in the corolla while it increases in the ovary after 48 h. This is caused by ethylene that is emitted from the flower coinciding with fertilization as this is not observed in transgenic ethylene insensitive plants (CaMV35S:etr1-1; 44568). Ethylene is also emitted from petunia vegetative tissue following mechanical wounding, resulting in an increase in PhBPBT expression in the leaves where expression is normally below detection levels. Indicative of this pattern of expression, we hypothesize that PhBPBT and subsequent benzyl benzoate production is involved in defense related processes in the corolla prior to pollination, in the ovary immediately following fertilization, and in vegetative tissue in response to wounding.