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

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.

Brachypodium: 20 years as a grass biology model system; the way forward?

“…An early example of this was the detoxification of the Fusarium head blight toxin, deoxynivalenol, by host uridine diphosphate glycosyltransferases [102]. More recently, fungal small RNAs encoded by Fusarium graminearum were shown to suppress host defence gene expression [103] and a similar approach could also be a feature of the Magnaporthe grisea infections [104]. B. distachyon also lent itself to the development of an infection system with Rhizoctonia solani, based on which 61 secreted protein effectors were identified that could manipulate the host [105] via WRKY transcription factors BdWRKY38 and BdWRKY44 [106,107].…”

Analysis of codon usage and allele frequencies reveal the double-edged nature of cross-kingdom RNAi

“…effectors(Werner et al 2021;Jian & Liang 2019). Again, we found that the Fg-sRNAs targeted regions were composed of codons with an unlikely high complementarity to the respective sRNA, compared to the rsRNAs (estimated ratio of PCHS and [95%-CI]: 0.711 [0.639, 0.791]; 0.732 [0.66, 0.813]; 0.801 [0.721, 0.89]) (Fig.…”

“…Fusarium graminearum(Werner et al 2021) in combination with the CDS from its host plant barley (Hordeum vulgare). Fg is an important plant pathogen with identified sRNA-…”

Extracellular vesicles isolated from dsRNA-sprayed barley plants exhibit no growth inhibition or gene silencing in Fusarium graminearum

“…In particular, the identification of plant EV-derived sRNAs stimulated a debate about whether EVs function as shuttles in interspecies communication, directing plant antifungal defence responses [2,7,44,[47][48][49]. Conversely, fungal pathogens secrete sRNAs to dampen plant immunity [13,29,57,58]. This sRNA-based crosstalk, also known as cross-species RNAi, was first described by Weiberg et al [57], demonstrating that the fungal pathogen Botrytis cinerea produces sRNAs that mimic plant sRNAs and bind to A. thaliana AGO1 to antagonistically silence important plant immunity genes [57].…”