Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2005
Publication Date: 5/20/2005
Citation: Underwood, B.A., Tieman, D.M., Shibuya, K., Dexter, R.J., Loucas, H.M., Simkin, A.J., Sims, C.A., Schmelz, E.A., Klee, H.J., Clark, D.G. 2005. Ethylene-regulated floral volatile synthesis in petunia corollas. Plant Physiology. 138:255-266. Interpretive Summary: Interpretive Summary: Plant volatiles mediate a wide range of ecological interactions including insect attraction and pollination of flowers and also act as scent-based beacons enabling the attraction of natural enemies to crop pests. In effort to beneficially modify plant volatile emission, it is essential to determine how these processes are biochemically regulated. 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 specific methyl transferase enzymes in petunia flowers are responsible for the production of methyl benzoate, the predominant floral fragrance volatile in this species. The production of these enzymes is strongly down regulated by pollination and the subsequent production of the plant hormone ethylene resulting in termination of floral volatile emission. Further evidence supporting the role of these enzymes was provided by transgenic silencing the methyl transferases and resulted in dramatically reduced methyl benzoate emission in the flowers. These quantitative changes in floral volatiles were also readily detectable by human scent panels. This research specifically identified terminal enzymes critical in floral volatile biosynthesis and phytohormones that control volatile production. This information will enable further advances in the engineering of plant volatile emission, examination of functional ecological hypothesis and ultimately the modification of agriculturally important plant-insect interactions.
Technical Abstract: Technical Abstract: In many flowering plants, such as petunia (Petunia x hybrida), ethylene produced in floral organs after pollination elicits a series of physiological and biochemical events, ultimately leading to senescence of petals and successful fertilization. Here, we demonstrate, using transgenic ethylene insensitive (44568) and Mitchell Diploid petunias, that multiple components of emission of volatile organic compounds (VOCs) are regulated by ethylene. Expression of benzoic acid/salicylic acid carboxyl methyltransferase (PhBSMT1 and 2) mRNA is temporally and spatially down-regulated in floral organs in a manner consistent with current models for postpollination ethylene synthesis in petunia corollas. Emission of methylbenzoate and other VOCs after pollination and exogenous ethylene treatment parallels a reduction in PhBSMT1 and 2mRNAlevels. Under cyclic light conditions (day/night), PhBSMT mRNA levels are rhythmic and precede emission of methylbenzoate by approximately 6 h. When shifted into constant dark or light conditions, PhBSMTmRNAlevels and subsequent methylbenzoate emission correspondingly decrease or increase to minimum or maximum levels observed during normal conditions, thus suggesting that light may be a more critical influence on cyclic emission of methylbenzoate than a circadian clock. Transgenic PhBSMT RNAi flowers with reduced PhBSMT mRNA levels show a 75% to 99% decrease in methylbenzoate emission, with minimal changes in other petunia VOCs. These results implicate PhBSMT1 and 2 as genes responsible for synthesis of methylbenzoate in petunia.