Fusarium graminearum DICER-like-dependent sRNAs are required for the suppression of host immune genes and full virulence

Bernhard Timo Werner,Jonas Engelhardt,Jens Steinbrenner,Karl-Heinz Kogel,Lukas Jelonek,Aline Koch,Ena Šečić,Richard A Wilson

doi:10.1371/journal.pone.0252365

Abstract

In filamentous fungi, gene silencing by RNA interference (RNAi) shapes many biological processes, including pathogenicity. Recently, fungal small RNAs (sRNAs) have been shown to act as effectors that disrupt gene activity in interacting plant hosts, thereby undermining their defence responses. We show here that the devastating mycotoxin-producing ascomycete Fusarium graminearum (Fg) utilizes DICER-like (DCL)-dependent sRNAs to target defence genes in two Poaceae hosts, barley (Hordeum vulgare, Hv) and Brachypodium distachyon (Bd). We identified 104 Fg-sRNAs with sequence homology to host genes that were repressed during interactions of Fg and Hv, while they accumulated in plants infected by the DCL double knock-out (dKO) mutant PH1-dcl1/2. The strength of target gene expression correlated with the abundance of the corresponding Fg-sRNA. Specifically, the abundance of three tRNA-derived fragments (tRFs) targeting immunity-related Ethylene overproducer 1-like 1 (HvEOL1) and three Poaceae orthologues of Arabidopsis thaliana BRI1-associated receptor kinase 1 (HvBAK1, HvSERK2 and BdSERK2) was dependent on fungal DCL. Additionally, RNA-ligase-mediated Rapid Amplification of cDNA Ends (RLM-RACE) identified infection-specific degradation products for the three barley gene transcripts, consistent with the possibility that tRFs contribute to fungal virulence via targeted gene silencing.

Highlights

RNA interference (RNAi) is a biological process in which small RNA molecules mediate gene silencing at the transcriptional or post-transcriptional level
Our data show that in the necrotrophic ascomycete Fusarium graminearum gene silencing by RNAi shapes its ability to cause disease, which is consistent with earlier results on the significance of the RNAi machinery in Fg [8, 35]
Pathogenicity relies on DICER-like (DCL)dependent small RNAs (sRNAs) that were identified as potential candidates for fungal effectors targeting defence genes in two Poaceae hosts, barley and Brachypodium

Summary

Introduction

RNA interference (RNAi) is a biological process in which small RNA (sRNA) molecules mediate gene silencing at the transcriptional or post-transcriptional level. In agriculture, RNAimediated silencing strategies have the potential to protect crops from pests and microbial pathogens [1,2,3,4,5]. Plants can be protected by foliar application of dsRNA to plants [10,11,12,13,14,15,16].

Results

Discussion

Conclusion