| Title: | Stearoyl-acyl carrier protein desaturases are associated with floral isolation in sexually deceptive orchids |
| Author(s): | Schluter PM; Xu S; Gagliardini V; Whittle E; Shanklin J; Grossniklaus U; Schiestl FP; |
| Address: | "Institutes of Systematic Botany, University of Zurich and Zurich-Basel Plant Science Center, CH-8008 Zurich, Switzerland. philipp.schlueter@systbot.uzh.ch" |
| ISSN/ISBN: | 1091-6490 (Electronic) 0027-8424 (Print) 0027-8424 (Linking) |
| Abstract: | "The orchids Ophrys sphegodes and O. exaltata are reproductively isolated from each other by the attraction of two different, highly specific pollinator species. For pollinator attraction, flowers chemically mimic the pollinators' sex pheromones, the key components of which are alkenes with different double-bond positions. This study identifies genes likely involved in alkene biosynthesis, encoding stearoyl-acyl carrier protein (ACP) desaturase (SAD) homologs. The expression of two isoforms, SAD1 and SAD2, is flower-specific and broadly parallels alkene production during flower development. SAD2 shows a significant association with alkene production, and in vitro assays show that O. sphegodes SAD2 has activity both as an 18:0-ACP Delta(9) and a 16:0-ACP Delta(4) desaturase. Downstream metabolism of the SAD2 reaction products would give rise to alkenes with double-bonds at position 9 or position 12, matching double-bond positions observed in alkenes in the odor bouquet of O. sphegodes. SAD1 and SAD2 show evidence of purifying selection before, and positive or relaxed purifying selection after gene duplication. By contributing to the production of species-specific alkene bouquets, SAD2 is suggested to contribute to differential pollinator attraction and reproductive isolation among these species. Taken together, these data are consistent with the hypothesis that SAD2 is a florally expressed barrier gene of large phenotypic effect and, possibly, a genic target of pollinator-mediated selection" |
| Keywords: | "Alkenes/*chemistry Base Sequence Bayes Theorem Flowers/chemistry/*enzymology *Genetic Speciation Isoenzymes/genetics Mixed Function Oxygenases/*genetics Models, Genetic Molecular Sequence Data Orchidaceae/*enzymology/genetics *Phylogeny Pollination/*genet;" |
| Notes: | "MedlineSchluter, Philipp M Xu, Shuqing Gagliardini, Valeria Whittle, Edward Shanklin, John Grossniklaus, Ueli Schiestl, Florian P eng Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. 2011/03/26 Proc Natl Acad Sci U S A. 2011 Apr 5; 108(14):5696-701. doi: 10.1073/pnas.1013313108. Epub 2011 Mar 21" |
