Elucidating the role of extracellular vesicles in the Barley-Fusarium interaction

Abstract

Fusarium graminearum (Fg) is a necrotrophic fungal pathogen that causes devastating diseases on its crop hosts barley and wheat. Recently, small RNAs (sRNAs) were identified as mobile communication signals between eukaryotes and their pathogens, symbionts or parasites. It has been shown that pathogens secrete sRNAs as effectors to suppress plant immunity and plants use endogenous sRNAs to resist infection, a phenomenon termed cross-kingdom RNAi; ckRNAi. However, little is known about the transport of fungus- or plant produced sRNAs to silence genes that contribute to immunity. Extracellular vesicles (EVs) are predicted playing a key role in the bidirectional transfer of sRNAs that mediate ckRNAi. To address this knowledge gap, we investigated the effects of EVs isolated from barley and Fg on their counterparts during plant-fungal interaction. Towards this, we developed a protocol for the isolation of EVs from Fg liquid cultures and assessed how Fg EVs contribute to fungal pathogenesis in barley using infiltration assays. To test the interdependence of EVs during Barley-Fg interaction, we treated Fg cultures with barley EVs. We found that infiltration of Fg EVs caused host specific phytotoxic effects in barley and barley EVs impaired Fg growth. Of note, Fg cultures showed an increase in purple pigmentation upon inoculation with barley EVs, suggesting a stress-induced premature formation of fruiting bodies. Together, our results demonstrate that EVs contribute to the Barley-Fg interaction, however, further studies are needed to unravel the nature of EV cargoes (e.g. protein and/or sRNA) responsible for affecting its plant/fungus counterpart.