A common theme in extracellular fluids of beetles: extracellular superoxide dismutases crucial for balancing ROS in response to microbial challenge.

Priska E. Streicher,Wilhelm Boland,Magdalena Stock,Anja S. Strauß,Natalie Wielsch,Antje Burse,René R. Gretscher,Ding Wang

doi:10.1038/srep24082

Priska E. Streicher, Wilhelm Boland + Show 6 more

Open Access

https://doi.org/10.1038/srep24082

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Journal: Scientific reports	Publication Date: Apr 12, 2016
Citations: 18	License type: CC BY 4.0

Affiliation: Max Planck Institute for Chemical Ecology

Abstract

Extracellular Cu/Zn superoxide dismutases (SODs) are critical for balancing the level of reactive oxygen species in the extracellular matrix of eukaryotes. In the present study we have detected constitutive SOD activity in the haemolymph and defensive secretions of different leaf beetle species. Exemplarily, we have chosen the mustard leaf beetle, Phaedon cochleariae, as representative model organism to investigate the role of extracellular SODs in antimicrobial defence. Qualitative and quantitative proteome analyses resulted in the identification of two extracellular Cu/Zn SODs in the haemolymph and one in the defensive secretions of juvenile P. cochleariae. Furthermore, quantitative expression studies indicated fat body tissue and defensive glands as the main synthesis sites of these SODs. Silencing of the two SODs revealed one of them, PcSOD3.1, as the only relevant enzyme facilitating SOD activity in haemolymph and defensive secretions in vivo. Upon challenge with the entomopathogenic fungus, Metarhizium anisopliae, PcSOD3.1-deficient larvae exhibited a significantly higher mortality compared to other SOD-silenced groups. Hence, our results serve as a basis for further research on SOD regulated host-pathogen interactions. In defensive secretions PcSOD3.1-silencing affected neither deterrent production nor activity against fungal growth. Instead, we propose another antifungal mechanism based on MRJP/yellow proteins in the defensive exudates.

Highlights

Using oxygen in aerobic metabolism provides more energy per glucose than glycolysis does and constitutes an evolutionary advantage
SOD3 has been conserved among metazoans, the first functional evidence for a SOD3 in insects has been reported from the ant Lasius niger not before the 21st century[17]
We have identified two extracellular SODs, PcSOD3.1 and PcSOD3.2, and one cytosolic variant, PcSOD1, in juvenile P. cochleariae

Summary

Introduction

Using oxygen in aerobic metabolism provides more energy per glucose than glycolysis does and constitutes an evolutionary advantage. Parasitoid wasps, for example, produce extracellular SODs and secrete them into their venom[21]. These exogenous SODs are suggested to increase the survival of the parasitoid eggs upon injection of the venom into an insect host during oviposition. In P. cochleariae, the defensive iridoid chrysomelidial is converted from imported 8-hydroxygeraniol glucoside[26,27,28,29,30,31] This transformation involves the hydrolysis of the glucoside and oxidation of the two primary hydroxy groups to produce the dialdehyde 8-oxogeranial, followed by a cyclisation step[29,32,33,34,35]. Besides in P. cochleariae, oxidation reactions in the defensive secretions of larvae can be found in related Chrysomelina species[29,36,37,38]

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