Central role of dsRNA in the elicitation of antiviral defenses in plants
Manfred Heinlein: Institut de Biologie Moléculaire des Plantes du CNRS (IBMP-CNRS)
<div>Plant viruses rely on macromolecular assembly and transport pathways for replication and for targeting the plasmodesmata (PD) for cell-to-cell movement. Our team investigates these processes in the context of plant defence responses and is interested to identify mechanisms leading to disease. We showed that mutants affected in the pathogen-recognition receptor (PRR) co-receptor kinase BAK1/SERK3 exhibit increased susceptibility to different RNA viruses, thus indicating a role of pattern-triggered immunity (PTI) in antiviral defense. Interestingly, Arabidopsis plants responded to crude extracts from virus-infected plants, but not to purified virions, showing that the molecules that elicit the antiviral PTI response are produced by the infected cell. Infection by RNA viruses is generally associated with the occurrence of double-stranded (ds)RNAs. Accordingly, we found that PTI is elicited by dsRNA. The application of dsRNAs and the synthetic dsRNA analog poly(I:C) to Arabidopsis plants induces typical PTI responses, including the activation of MPK6 and MPK3, ethylene synthesis and defense gene expression. Moreover, poly(I:C) treatment induces seedling growth inhibition, a phenotype associated with the activation of plant immunity. Consistent with the hypothesis that dsRNAs are perceived as viral pathogen-associated molecular patterns (PAMPs) in plants, dsRNA treatment can protect plants against virus infection. The PTI responses were not impaired in plants lacking dicer-like (DCL) proteins indicating that DCLs do not serve as the dsRNA receptors leading to PTI. The dsRNA receptors involved in the triggering of PTI as well as the downstream mechanisms that restrict virus infection may be identified by future studies.</div>
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