Double‐stranded RNA s induce a pattern‐triggered immune signaling pathway in plants

Pattern‐triggered immunity ( PTI ) is a plant defense response that relies on the perception of conserved microbe‐ or pathogen‐associated molecular patterns ( MAMP s or PAMP s, respectively). Recently, it has been recognized that PTI restricts virus infection in plants; however, the nature of the viral or infection‐induced PTI elicitors and the underlying signaling pathways are still unknown. As double‐stranded RNA s (ds RNA s) are conserved molecular patterns associated with virus replication, we applied ds RNA s or synthetic ds RNA analogs to Arabidopsis thaliana and investigated PTI responses. We show that in vitro‐ generated ds RNA s, ds RNA s purified from virus‐infected plants and the ds RNA analog polyinosinic–polycytidylic acid (poly(I:C)) induce typical PTI responses dependent on the co‐receptor SOMATIC EMBRYOGENESIS RECEPTOR‐LIKE KINASE 1 ( SERK 1), but independent of dicer‐like ( DCL ) proteins in Arabidopsis. Moreover, ds RNA treatment of Arabidopsis induces SERK 1‐dependent antiviral resistance. Screening of Arabidopsis wild accessions demonstrates natural variability in ds RNA sensitivity. Our findings suggest that ds RNA s represent genuine PAMP s in plants, which induce a signaling cascade involving SERK 1 and a specific ds RNA receptor. The dependence of ds RNA ‐mediated PTI on SERK 1, but not on DCL s, implies that ds RNA ‐mediated PTI involves membrane‐associated processes and operates independently of RNA silencing. ds RNA sensitivity may represent a useful trait to increase antiviral resistance in cultivated plants.