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Published on: November 21, 2018
Destruxin A inhibits scavenger receptor B mediated melanization in Aphis citricola
Pengfei Han1,2, Qitian Gong1,2, Jiqiao Fan2,3
1Institute of Applied Biology and College of Life Science, Shanxi University, Taiyuan, China.
Background:
Destruxin A (DA) is a mycotoxin secreted by entomogenous fungi, such as Metarhizium anisopliae, which has broad-spectrum insecticidal activity. Insect innate immunity provides resistance against the invasion of entomopathogenic fungi. Previous studies have shown that DA could inhibit the immune response, however, the suppressive mechanism of DA on prophenoloxidase system is still unknown.
Results:
Based on the transcriptome of Aphis citricola, we screened the scavenger receptor class B(AcSR-B)and identified that it significantly responds to DA. Spatio-temporal expression analysis showed that AcSR-B is highly expressed in adult stage and is mainly distributed in the abdominal region. We further revealed that both M. anisopliae and Escherichia coli could suppress the expression of AcSR-B at 24 h, and that the expressed recombinant protein rAcSR-B possessed agglutination activity to M. anisopliae and E. coli. DA could suppress the protein expression of AcSR-B. In addition, RNA interference of AcSR-B caused death of A. citricola in a dose-dependent manner, and RNA interference of AcSR-B increased mortality in A. citricola under the same lethal concentration of DA. The inhibiting effect of AcSR-B silencing was similar with the DA treatment upon phenol oxidase (PO) activity of A. citricola hemolymph. DA could not decrease PO activity further after AcSR-B silencing.
Conclusion:
Destruxin A inhibits melanization by suppressing AcSR-B in A. citricola. Our findings are helpful in understanding the underlying molecular mechanism of the DA suppressing immune system, and uncover a potential molecular target for double-stranded RNA (dsRNA) insecticides.
Insights
Destruxin A (DA) mycotoxin suppresses insect immunity by targeting scavenger receptor class B (AcSR-B) in Aphis citricola. This mechanism reveals a potential target for novel dsRNA insecticides.
Area of Science:
- Insect immunology
- Mycotoxicology
- Molecular biology
Background:
- Destruxin A (DA) is a mycotoxin from Metarhizium anisopliae with insecticidal properties.
- Insect innate immunity combats fungal infections, but DA's mechanism on the prophenoloxidase system is unclear.
Purpose of the Study:
- To elucidate the suppressive mechanism of DA on the prophenoloxidase system in Aphis citricola.
- To identify molecular targets for DA's immune suppression.
Main Methods:
- Transcriptome analysis to identify DA-responsive genes.
- Spatio-temporal expression analysis of scavenger receptor class B (AcSR-B).
- RNA interference (RNAi) to assess AcSR-B function and its interaction with DA.
Main Results:
- AcSR-B expression is significantly induced by DA and suppressed by M. anisopliae and E. coli.
- Recombinant AcSR-B protein exhibits agglutination activity against M. anisopliae and E. coli.
- DA suppresses AcSR-B protein levels; AcSR-B RNAi increases A. citricola mortality and mimics DA's effect on phenol oxidase activity.
Conclusions:
- DA inhibits melanization in A. citricola by suppressing AcSR-B.
- AcSR-B is a key mediator of DA's immune suppressive effects.
- AcSR-B represents a potential molecular target for developing dsRNA insecticides.
