Role of Dicer-Dependent RNA Interference in Regulating Mycoparasitic Interactions.

Dicer-like proteins (DCLs) play a vital role in RNA interference (RNAi), by cleaving RNA filament into small RNAs. Although DCL-mediated RNAi can regulate interspecific communication between pathogenic/mutualistic organisms and their hosts, its role in mycoparasitic interactions is yet to be investigated. In this study, we deleted genes in the mycoparasitic fungus and characterize the functions of DCL-dependent RNAi in mycoparasitism. Deletion of resulted in a mutant with reduced secondary metabolite production, antagonism toward the plant-pathogenic fungus , and reduced ability to control Fusarium foot rot disease on wheat, caused by Fusarium graminearum. Transcriptome sequencing of the interaction between the Δ strain and or F. graminearum identified the downregulation of genes coding for transcription factors, membrane transporters, hydrolytic enzymes, and secondary metabolites biosynthesis enzymes putatively involved in antagonistic interactions, in comparison with the wild-type interaction. A total of 61 putative novel microRNA-like RNAs (milRNAs) were identified in , and 11 were downregulated in the Δ mutant. In addition to putative endogenous gene targets, these milRNAs were predicted to target . and F. graminearum virulence factor genes, which showed an increased expression during interaction with the Δ mutant incapable of producing the targeting milRNAs. In summary, this study constitutes the first step in elucidating the role of RNAi in mycoparasitic interactions, with important implications for biological control of plant diseases, and poses the base for future studies focusing on the role of cross-species RNAi regulating mycoparasitic interactions. Small RNAs mediated RNA interference (RNAi) known to regulate several biological processes. Dicer-like endoribonucleases (DCLs) play a vital role in the RNAi pathway by generating sRNAs. In this study, we investigated a role of DCL-mediated RNAi in interference interactions between mycoparasitic fungus and the two fungal pathogens and Fusarium graminearum (here called mycohosts). We found that the mutants were not able to produce 11 sRNAs predicted to finetune the regulatory network of genes known to be involved in production of hydrolytic enzymes, antifungal compounds, and membrane transporters needed for antagonistic action of . We also found . sRNAs putatively targeting known virulence factors in the mycohosts, indicating RNAi-mediated cross-species communication. Our study expanded the understanding of underlying mechanisms of cross-species communication during interference interactions and poses a base for future works studying the role of DCL-based cross-species RNAi in fungal interactions.