Abstract
Insecticidal fungi represent a promising alternative to chemical pesticides for disease vector control. Here, we show that the pathogenic fungus Beauveria bassiana exports a microRNA-like RNA (bba-milR1) that hijacks the host RNA-interference machinery in mosquito cells by binding to Argonaute 1 (AGO1). bba-milR1 is highly expressed during fungal penetration of the mosquito integument, and suppresses host immunity by silencing expression of the mosquito Toll receptor ligand Spätzle 4 (Spz4). Later, upon entering the hemocoel, bba-milR1 expression is decreased, which avoids induction of the host proteinase CLIPB9 that activates the melanization response. Thus, our results indicate that the pathogen deploys a cross-kingdom small-RNA effector that attenuates host immunity and facilitates infection.
Highlights
Insecticidal fungi represent a promising alternative to chemical pesticides for disease vector control
We identified four miRNA-like small RNAs whose sequences cannot be mapped to the A. stephensi genome, but perfectly matched the B. bassiana genome (Supplementary Fig. 1a)
These results indicate that miRNAs produced by B. bassiana are exported into host cells and bind to mosquito Argonaute 1 (AGO1) to hijack host the RNA interference (RNAi) machinery
Summary
Insecticidal fungi represent a promising alternative to chemical pesticides for disease vector control. The insect pathogenic fungus Beauveria bassiana (Cordycipitaceae) offers a promising environment-friendly alternative to chemical insecticides[5,6]. This fungus is effective at killing both insecticide-resistant and -susceptible adult mosquitoes[7,8] and considered as a next-generation mosquito control agent[9,10]. Toll is the principal antifungal pathway by directing the production of antifungal peptides[12] Melanization is another important facet of the mosquito immune defense against fungi[13]. To our knowledge, no examples of such effector molecules have been described for insect pathogenic fungi[20]
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