Characterization of an antennal carboxylesterase from the pest moth Spodoptera littoralis degrading a host plant odorant.
BACKGROUND
Carboxyl/cholinesterases (CCEs) are highly diversified in insects. These enzymes have a broad range of proposed functions, in neuro/developmental processes, dietary detoxification, insecticide resistance or hormone/pheromone degradation. As few functional data are available on purified or recombinant CCEs, the physiological role of most of these enzymes is unknown. Concerning their role in olfaction, only two CCEs able to metabolize sex pheromones have been functionally characterized in insects. These enzymes are only expressed in the male antennae, and secreted into the lumen of the pheromone-sensitive sensilla. CCEs able to hydrolyze other odorants than sex pheromones, such as plant volatiles, have not been identified.


METHODS
In Spodoptera littoralis, a major crop pest, a diversity of antennal CCEs has been previously identified. We have employed here a combination of molecular biology, biochemistry and electrophysiology approaches to functionally characterize an intracellular CCE, SlCXE10, whose predominant expression in the olfactory sensilla suggested a role in olfaction. A recombinant protein was produced using the baculovirus system and we tested its catabolic properties towards a plant volatile and the sex pheromone components.


CONCLUSIONS
We showed that SlCXE10 could efficiently hydrolyze a green leaf volatile and to a lesser extent the sex pheromone components. The transcript level in male antennae was also strongly induced by exposure to this plant odorant. In antennae, SlCXE10 expression was associated with sensilla responding to the sex pheromones and to plant odours. These results suggest that a CCE-based intracellular metabolism of odorants could occur in insect antennae, in addition to the extracellular metabolism occurring within the sensillar lumen. This is the first functional characterization of an Odorant-Degrading Enzyme active towards a host plant volatile.
UMR-A 1272 UPMC-INRA Physiologie de l'Insecte, Université Pierre et Marie Curie and INRA, Paris and Versailles, France.
Nicolas
N
Durand
Gerard
G
Carot-Sans
Thomas
T
Chertemps
Françoise
F
Bozzolan
Virginie
V
Party
Michel
M
Renou
Stéphane
S
Debernard
Gloria
G
Rosell
Martine
M
Maïbèche-Coisne
D000818:Animals; D015153:Blotting, Western; D043182:Carboxylesterase / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006790:Host-Parasite Interactions; D006868:Hydrolysis; D017403:In Situ Hybridization; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009812:Odorants; D018034:Olfactory Receptor Neurons / Q000201:enzymology; D018515:Plant Leaves / Q000378:metabolism / Q000469:parasitology; D010944:Plants / Q000378:metabolism* / Q000469:parasitology; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012724:Sex Attractants / Q000378:metabolism; D018411:Spodoptera / Q000201:enzymology* / Q000254:growth & development / Q000502:physiology; D055549:Volatile Organic Compounds / Q000378:metabolism
D019476:Insect Proteins; D011994:Recombinant Proteins; D012724:Sex Attractants; D055549:Volatile Organic Compounds; D043182:Carboxylesterase