Perception of double‐stranded RNA in plant antiviral immunity

Abstract

Summary RNA silencing and antiviral pattern‐triggered immunity (PTI) both rely on recognition of double‐stranded (ds)RNAs as defence‐inducing signals. While dsRNA recognition by dicer‐like proteins during antiviral RNA silencing is thoroughly investigated, the molecular mechanisms involved in dsRNA perception leading to antiviral PTI are just about to be untangled. Parallels to antimicrobial PTI thereby only partially facilitate our view on antiviral PTI. PTI against microbial pathogens involves plasma membrane bound receptors; however, dsRNAs produced during virus infection occur intracellularly. Hence, how dsRNA may be perceived during this immune response is still an open question. In this short review, we describe recent discoveries in PTI signalling upon sensing of microbial patterns and endogenous ‘danger’ molecules with emphasis on immune signalling‐associated subcellular trafficking processes in plants. Based on these studies, we develop different scenarios how dsRNAs could be sensed during antiviral PTI.

Evidence That Phosphorylation of the α-Subunit of eIF2 Does Not Essentially Inhibit mRNA Translation in Wheat Germ Cell-Free System

“…Taking into consideration that there is no PKR equivalent in plants (Lageix et al, 2008;Zhang et al, 2008), this result most likely can be explained by nonspecific activation of endogenous TaGCN2, resulting in phosphorylation of TaeIF2a, while protein synthesis inhibition could be due to parallel activation of RNAprocessing bodies, which may prevent BMV RNA from being translated. A similar explanation could be applicable for the recent work (Niehl and Heinlein, 2019) in which leaf discs of Arabidopsis were treated by very high concentration (0.5 mg/ml) of poly(rI-rC) that (unlike the ssRNA) induced obvious phosphorylation of AteIF2a. Unfortunately, the concomitant changes in protein synthesis were not measured in that study.…”

Plant Molecular Responses to Potato Virus Y: A Continuum of Outcomes from Sensitivity and Tolerance to Resistance

“…Recently, it has been accepted that the first layer of the innate immunity against pathogenic bacteria that relies on the recognition of microbial-or pathogen-associated molecular patterns (MAPMs or PAMPs) by transmembrane pattern recognition receptors (PRRs), PAMP-triggered immunity (PTI) [34], also acts against viruses [35][36][37]. However, how viral double-stranded RNA (dsRNA) could be sensed during PTI is still unknown [38]. As a second layer of the immune system, plants also employ effector-triggered immunity (ETI) against viruses [33].…”

Suppression of RNA-dependent RNA polymerase 6 in tomatoes allows potato spindle tuber viroid to invade basal part but not apical part including pluripotent stem cells of shoot apical meristem

“…Recently, pathogen-associated molecular patterns (PAMPs)-triggered immunity (PTI) that contributes to plant basal resistance has been discovered to act against viruses in plants, and dsRNA was shown to induce typical PTI responses by recognition as a genuine PAMP [67,68]. Antiviral PTI induced by dsRNA is to be a distinct plant defense pathway from RNA silencing because PTI responses are not impaired in A. thaliana dcl2 dcl4, dcl2 dcl3 dcl4 or dcl1 mutants, although the two pathways may be functionally linked [68,69]. Earliest signaling events in PTI responses include, for instance, the influx of Ca 2+ , the production of reactive oxygen species, and the activation of mitogen-activated protein kinase (MAPK) cascades [70].…”

“…Antiviral PTI induced by dsRNA is to be a distinct plant defense pathway from RNA silencing because PTI responses are not impaired in A . thaliana dcl2 dcl4 , dcl2 dcl3 dcl4 or dcl1 mutants, although the two pathways may be functionally linked [ 68 , 69 ]. Earliest signaling events in PTI responses include, for instance, the influx of Ca 2+ , the production of reactive oxygen species, and the activation of mitogen-activated protein kinase (MAPK) cascades [ 70 ].…”