Dicer functions transcriptionally and posttranscriptionally in a multilayer antiviral defense

Significance Posttranscriptional RNA interference-mediated antiviral defense is well conserved, in which the key players, Dicer and Argonaute, act to digest viral RNAs. Utilizing a filamentous fungus model, we have previously shown the Spt–Ada–Gcn5 acetyltransferase (SAGA) transcriptional activator to regulate the upregulation of the two main antiviral RNA-silencing components, dicer-like 2 ( dcl2 ) and argonaute-like 2 ( agl2 ). Here, we show an additional distinct functional role for DCL2 in the virus-responsive, SAGA-mediated transcriptional upregulation of a subset of host genes. Strikingly, certain upregulated genes contribute to mitigate viral symptom induction. No involvement of Argonaute in this Dicer function is suggested by the agl2 disruption assay. Therefore, DCL2 is bifunctional in dual-layer antiviral defense to inhibit viral replication and alleviate symptom expression.