Virus resistance induced by NB-LRR proteins involves Argonaute4-dependent translational control

Active resistance to viruses is afforded by plant disease resistance (R) genes, which encode proteins with nucleotide-binding (NB) and leucine-rich repeat (LRR) domains. Upon recognition of pathogen-derived elicitors, these NB-LRR proteins are thought to initiate a number of signaling pathways that lead to pathogen restriction. However, little is known about the molecular mechanisms that ultimately curtail virus accumulation. Here, we show that the co-expression of a plant NB-LRR protein with its cognate elicitor results in an antiviral response that inhibits the translation of virus-encoded proteins in Nicotiana benthamiana. This antiviral response is dependent on viral cis elements, and, upon activation of the NB-LRR protein, viral transcripts accumulate but do not associate with ribosomes. The induced inhibition of viral transcript translation and NB-LRR-mediated virus resistance were compromised by the downregulation of Argonaute4-like genes. Argonaute proteins have been implicated in small RNA-mediated RNA degradation, and in degradation-independent translational control. Our results suggest that the engagement of Argonaute proteins in the specific translational control of viral transcripts is a key factor in virus resistance mediated by NB-LRR proteins.