Small RNAs in plant defense responses during viral and bacterial interactions: similarities and differences

Abstract

Small non-coding RNAs constitute an important class of gene expression regulators that control different biological processes in most eukaryotes. In plants, several small RNA (sRNA) silencing pathways have evolved to produce a wide range of small RNAs with specialized functions. Evidence for the diverse mode of action of the small RNA pathways has been highlighted during plant–microbe interactions. Host sRNAs and small RNA silencing pathways have been recognized as essential components of plant immunity. One way plants respond and defend against pathogen infections is through the small RNA silencing immune system. To deal with plant defense responses, pathogens have evolved sophisticated mechanisms to avoid and counterattack this defense strategy. The relevance of the small RNA-mediated plant defense responses during viral infections has been well-established. Recent evidence points out its importance also during plant–bacteria interactions. Herein, this review discusses recent findings, similarities and differences about the small RNA-mediated arms race between plants and these two groups of microbes, including the small RNA silencing pathway components that contribute to plant immune responses, the pathogen-responsive endogenous sRNAs and the pathogen-delivered effector proteins.

Expression of Cucumber mosaic virus suppressor 2b alters FWA methylation and its siRNA accumulation in Arabidopsis thaliana

“…However, accumulation of endogenous siRNAs affected by 2b is in contrast to ago4 mutant, which deploys 2b engendered siRNA sequestration to limit its availability to AGO4 for target loci methylation. The ability to sequester siRNA is common amongst suppressor proteins, however, the sequestered siRNA size may vary; for instance, P19 binds with 21nt miRNA duplexes while Flock house virus (FHV) B2 protein binds with longer siRNAs (Pelaez and Sanchez, 2013). This eludes 2b's role in sustaining AGO4 function endogenously.…”

The Evolutionary Fate of the Horizontally Transferred Agrobacterial Mikimopine Synthase Gene in the Genera Nicotiana and Linaria

“…Based on the current knowledge of the role of small RNAs in interactions between plant hosts and bacteria [82], we can speculate on the influence of naturally occurring small RNAs produced from the mis gene in N. tabacum , which could block a further infection event by the mikimopine-type of A. rhizogenes . The putative mechanism may be based on endogenous siRNAs derived from the horizontally transferred mis gene or the mis gene transcripts may serve as permanent activator(s) of defence mechanisms.…”

Sense- and antisense-mediated resistance against Sri Lankan cassava mosaic virus (SLCMV) in Nicotiana benthamiana

“…These siRNAs can direct sequencespecific degradation of target viral transcripts to promote antiviral silencing in plants. Several lines of evidence, coming from the studies of siRNAs and viral pathogenesis (Wang et al 2012, Peláez andSanchez 2013), have led to the understanding of cytoplasmic RNA silencing, also referred to as post-transcriptional gene silencing (PTGS). The PTGS acts as a ubiquitous plant defense response against most RNA-viruses and transcripts produced by DNA-viruses such as geminiviruses.…”