PT - JOURNAL ARTICLE AU - Fatima Yousif Gaffar AU - Jafargholi Imani AU - Petr Karlovsky AU - Aline Koch AU - Karl-Heinz Kogel TI - Various components of the RNAi pathway are required for conidiation, ascosporogenesis, virulence, DON production and SIGS-mediated fungal inhibition by exogenous dsRNA in the Head Blight pathogen <em>Fusarium graminearum</em> AID - 10.1101/633099 DP - 2019 Jan 01 TA - bioRxiv PG - 633099 4099 - http://biorxiv.org/content/early/2019/05/14/633099.short 4100 - http://biorxiv.org/content/early/2019/05/14/633099.full AB - Gene silencing through RNA interference (RNAi) shapes many biological processes in filamentous fungi. In this study we explored the contribution of several key proteins of fungal RNAi pathways, including DICER-like1 and 2 (FgDCL1, FgDCL2), ARGONAUTE1 and 2 (FgAGO1, FgAGO2), AGO-interacting protein FgQIP (QDE2-interacting protein), RecQ helicase (FgQDE3), and four RNA-dependent RNA polymerases (FgRdRP1, FgRdRP2, FgRdRP3, FgRdRP4), to sexual and asexual multiplication, pathogenicity as well as spray-induced gene silencing (SIGS) by exogenous dsRNA of the ascomycete fungus Fusarium graminearum (Fg). We corroborate and extend earlier findings that conidiation, ascosporogenesis and Fusarium Head Blight (FHB) symptom development require operable RNAi pathways. Of note, the involvement of RNAi components in conidiation is dependent on environmental conditions as it is detectable only under low light (&lt; 2 μmol m−2 s−1). Although both DCLs and AGOs partially share their functions, the sex-specific RNAi pathway (ascosporogenesis) is mediated primarily by FgDCL1 and FgAGO2, while the RNAi components FgDCL2 and FgAGO1 contribute to conidia formation and germination. Similarly, FgDCL1 and FgAGO2 account for pathogenesis as their knock-out (KO) results in reduced FHB development. Apart from Δdcl2 and Δago1, the KO mutants Δrdrp2, Δrdrp3, Δrdrp4, Δqde3 and Δqip are strongly compromised for conidiation, while KO mutations in all RdPRs, QDE3 and QIP strongly affect ascosporogenesis. Analysis of trichothecenes mycotoxins in wheat kernels showed that the relative amount of DON [rDON], calculated as [DON] per amount of fungal genomic DNA, was reduced in all spikes infected with RNAi mutants, suggesting that fungal RNAi pathways affect Fg’s DON production in wheat spikes. Moreover, SIGS-mediated plant protection to Fusarium was strongly dependent on fungal DCLs, AGOs, and QIP, but not on QDE3. Together these data show that in F. graminearum the RNAi machinery plays a central role in different steps of sexual and asexual reproduction, in fungal pathogenicity and DON production, and in the control of the pathogen by exogenous dsRNA under the tested conditions.