Co-agroinfiltration of mGFP and VSRs were done at 0

Co-agroinfiltration of mGFP and VSRs were done at 0.5 OD. Protein extraction and gel blot analysis For transgenic plants, a solution of 25 g/ml Dexametasone supplemented with 0.1% v/v Silwet L-77 was sprayed onto leaves of 5 week-old transgenic plants. post agroinfiltration of both, wild type and plants. Lower panel shows Ponceau Red staining of ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco) for confirmation of equal loading. Experiments were repeated three times and showed comparable results.(TIF) ppat.1003435.s003.tif (166K) GUID:?A297DE83-F685-449D-B714-DD1BF7CF7544 Abstract RNA silencing mediated by small RNAs (sRNAs) is a conserved regulatory process with key Schisantherin A antiviral and antimicrobial functions in eukaryotes. A common counter-defensive strategy of viruses against RNA silencing Schisantherin A is usually to deploy viral suppressors of RNA silencing (VSRs), epitomized by the P19 protein of tombusviruses, which sequesters sRNAs and compromises their downstream action. Here, we provide evidence that specific species are able to sense and, in turn, antagonize the effects of P19 by activating a highly potent immune response that protects tissues against contamination. This immunity is usually salicylate- and ethylene-dependent, and occurs without microscopic cell death, providing an example of extreme resistance (ER). We show that the capacity of P19 to bind sRNA, which is usually mandatory for its VSR function, is also necessary to induce ER, and that effects downstream of P19-sRNA complex formation are the likely determinants of the induced resistance. Accordingly, VSRs unrelated to P19 that also bind sRNA compromise the onset of P19-elicited defense, but do not alter a resistance phenotype conferred by a viral protein without VSR activity. These results show that plants have developed specific responses against the damages incurred by VSRs to the cellular silencing machinery, a likely necessary step in the never-ending molecular arms race opposing pathogens to their hosts. Author Schisantherin A Summary Multiple and complex layers of defense help plants to combat pathogens. A first line of defense relies on the detection, via dedicated host-encoded receptors, of signature molecules (so called pathogen-associated molecular patterns, PAMPs) produced by pathogens. In turn, Schisantherin A this PAMP-triggered immunity (PTI) may be itself antagonized by adapted pathogens that have developed virulence effectors to target key PTI components. Host plants react to PTI suppression by generating disease resistance (R) proteins that identify virulence effectors and activate highly specific resistance called Effector Triggered Immunity (ETI). It has been noted that RNA silencing, a sequence-specific antiviral defense response based on the production of virus-derived 21C24 nt small RNAs on the one hand, and its suppression by virulence effectors, called viral suppressors of RNA silencing (VSRs) around the other, are conceptually much like PTI. Here we provide strong support to this hypothesis by showing that extreme resistance is indeed activated following detection, in specific host Schisantherin A species, of the VSR activity of a COPB2 viral virulence effector. The ensuing antiviral immunity displays many characteristics of ETI, suggesting that one or several R proteins must sense the integrity of the host silencing machinery. Introduction Plants fight microbial attacks using both constitutive and induced defenses, which include basal and highly specific resistance [1]. Basal resistance, or PTI (for PAMP-Triggered Immunity), often relies on the detection of highly conserved signature molecules that include fungal polysaccharides or bacterial flagellin, collectively termed pathogen-associated molecular patterns (PAMPs; [1], [2]). To circumvent this first layer of defense, many host-adapted microbes produce effector proteins that suppress numerous actions of PTI [3]. As a counter-response, plants have, in turn, developed classes of specialized receptors called resistance (R) proteins that directly detect pathogen’s encoded suppressors of PTI, or that sense the molecular effects of their adverse action on defense-related host factors. R protein activation triggers potent defense responses collectively named Effector Triggered Immunity (ETI) that often Calbeit not always (observe below) culminate in Hypersensitive Response (HR), a rapid and localized cell death process thought to limit or preclude pathogens’ growth [1], [2]. As a consequence of the gene-for-gene type of conversation linking these two components, herb R genes and their corresponding pathogen-encoded virulence factors evolve constantly.