LAUSR

BACKGROUND AND AIMS Plants have evolved complex mechanisms to fight against pathogens. Within this mechanisms, pattern-triggered immunity (PTI) relies on the recognition of conserved microbe- or pathogen-associated molecular patterns (MAMPs or PAMPs, respectively) by membrane bound receptors. Indeed, PTI restricts virus infection in plants and, in addition, BRI1-associated kinase 1 (BAK1), a central regulator of PTI, plays a role in antiviral resistance. However, the compounds that trigger antiviral defences, along with their molecular mechanisms of action, remain mostly elusive. Herein, we explore the role of a fungal extracellular subtilase named AsES in its capacity to trigger antiviral responses. METHODS In this study, we obtained AsES by recombinant expression, evaluated and characterized its capacity to trigger antiviral responses against tobacco mosaic virus (TMV), by performing time course experiments, analyzing gene expression, virus movement and callose deposition experiments. KEY RESULTS The results in this study provide direct evidence that the exogenous treatment with recombinant AsES increases a state of resistance against TMV infection, both in Arabidopsis and Nicotiana benthamiana plants. Also, the antiviral PTI response exhibited by AsES in Arabidopsis is mediated by the BAK1/SERK3 and BKK1/SERK4 co-receptors. Moreover, AsES requires a fully active salicylic acid (SA) signalling pathway to restrict the TMV movement by inducing callose deposition. Additionally, treatment with PSP1, a biostimulant based on AsES as the active compound, showed an increased resistance against TMV in N. benthamiana and tobacco plants. CONCLUSIONS AsES is a fungal serine protease which triggers antiviral responses relying on a conserved mechanism by means of the salicylic acid signalling pathway and could be exploited as an effective and sustainable biotechnology strategy for viral disease management in plants.