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Title: Amino Acid Change in an Orchid Desaturase Enables Mimicry of the Pollinator’s Sex Pheromone

Here, we show that mimicry illustrates the power of selection to produce phenotypic convergence in biology. A striking example is the imitation of female insects by plants that are pollinated by sexual deception of males of the same insect species. This involves mimicry of visual, tactile, and chemical signals of females, especially their sex pheromones. The Mediterranean orchid Ophrys exaltata employs chemical mimicry of cuticular hydrocarbons, particularly the 7-alkenes, in an insect sex pheromone to attract and elicit mating behavior in its pollinators, males of the cellophane bee Colletes cunicularius. A difference in alkene double-bond positions is responsible for reproductive isolation between O. exaltata and closely related species, such as O. sphegodes. We show that these 7-alkenes are likely determined by the action of the stearoyl-acyl-carrier-protein desaturase (SAD) homolog SAD5. After gene duplication, changes in subcellular localization relative to the ancestral housekeeping desaturase may have allowed proto-SAD5’s reaction products to undergo further biosynthesis to both 7- and 9-alkenes. Such ancestral coproduction of two alkene classes may have led to pollinator-mediated deleterious pleiotropy. Despite possible evolutionary intermediates with reduced activity, amino acid changes at the bottom of the substrate-binding cavity have conferred enzyme specificity for 7-alkene biosynthesis by preventing the bindingmore » of longer-chained fatty acid (FA) precursors by the enzyme. In conclusion, this change in desaturase function enabled the orchid to perfect its chemical mimicry of pollinator sex pheromones by escape from deleterious pleiotropy, supporting a role of pleiotropy in determining the possible trajectories of adaptive evolution.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [2] ;  [1]
  1. Univ. of Zurich, Zurich (Switzerland). Dept. of Systematic and Evolutionary Botany and Zurich-Basel Plant Science Center
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Dept. of Biology
  3. Univ. of Zurich, Zurich (Switzerland). Dept. of Plant and Microbial Biology and Zurich-Basel Plant Science Center
Publication Date:
OSTI Identifier:
1335436
Report Number(s):
BNL--112099-2016-JA
Journal ID: ISSN 0960-9822
Grant/Contract Number:
SC0012704; KC0304000; 31003A_130796; 31003A_141245
Type:
Accepted Manuscript
Journal Name:
Current Biology
Additional Journal Information:
Journal Volume: 26; Journal Issue: 11; Journal ID: ISSN 0960-9822
Publisher:
Elsevier
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES