The Tombusvirus-encoded P19: from irrelevance to elegance

Since its discovery in the late 1980s, the status of the Tombusvirus-encoded p19 protein (P19) changed from being thought obsolete to its identification a decade later as an important viral pathogenicity factor. The recent finding that P19 suppresses RNA interference (RNAi) by appropriating short interfering RNAs led to its widespread use as an RNAi-probing tool in various plant and animal models. Here, I discuss how our knowledge of p19 has developed over the years, with emphasis on the relevance of understanding its biological roles during Tombusvirus infection of plants.