Plant Small RNA Species Direct Gene Silencing in Pathogenic Bacteria as well as Disease Protection

Abstract

Plant small RNAs (sRNAs) and/or double-stranded RNAs (dsRNAs) trigger RNA interference (RNAi) in interacting eukaryotic pathogens or parasites. However, it is unknown whether this phenomenon could operate in bacterial phytopathogens, which lack a eukaryoticlike RNAi machinery. Here, we first show that Arabidopsis-encoded inverted repeat transgenes trigger silencing of Pseudomonas syringae heterologous reporter and endogenous virulence-associated genes during infection. Antibacterial Gene Silencing (AGS) of the latter was associated with a reduced pathogenesis, which was also observed upon application of corresponding plant-derived RNAs onto wild-type plants prior to infection. We additionally demonstrate that sRNAs directed against virulence factor transcripts were causal for silencing and pathogenesis reduction, while cognate long dsRNAs were inactive. Overall, this study provides the first evidence that plant sRNAs can directly reprogram gene expression in a phytopathogenic bacterium and may have wider implications in the understanding of how plants regulate transcriptome, community composition and genome evolution of associated bacteria.

Growing pains: addressing the pitfalls of plant extracellular vesicle research

“…To date, four reports suggest that plant EVs are also associated with RNA molecules. Unfortunately, two of these reports analyzed crude EV pellets that most certainly contained co‐isolated contaminants (Cai et al ., 2018; Singla‐Rastogi et al ., 2019). The other two analyzed density‐gradient purified EVs, but did not test to confirm the RNAs were contained within EVs (Baldrich et al ., 2019; Hou et al ., 2019).…”

“…The discovery that isolated plant EVs are associated with RNAs has led many to speculate that, similar to mammalian EVs, plant EVs could traffic regulatory small RNAs (sRNAs) throughout a plant and even into invading pathogens (Cai et al ., 2018; Baldrich et al ., 2019; Hou et al ., 2019). In fact, studies are already claiming to have evidence for EV‐mediated trans‐kingdom silencing (Cai et al ., 2018; Singla‐Rastogi et al ., 2019). Despite these claims, the current evidence is not strong enough to firmly establish any function for plant EVs.…”

An atypical class of non-coding small RNAs produced in rice leaves upon bacterial infection

“…However, it is doubtful that xisRNA or their precursor are of bacterial origin because their sequences poorly match the genomic sequences of the bacterial triggers (Supplementary Figure S12). An alternative working model that appears less likely but that cannot be discounted is that rice generates xisRNAs that act in the bacterial cell to direct gene silencing and mitigate bacterial invasiveness similar to what has been reported for the bacterial plant pathogen Pseudomonas syringae (81) and gut bacteria (82).…”

Extracellular RNA: mechanisms of secretion and potential functions

“…The resulting nucleotides are taken up by the pathogen for use as a phosphate source to maintain fungal growth during infection ( Mukherjee et al , 2020 ) (4). Plants can send naked siRNA or EV-associated siRNAs into bacterial pathogens to silence virulence factors and reduce pathogenesis ( Singla-Rastogi et al , 2019 ) (5). sRNAs and long dsRNAs secreted by plants may be transferred between adjacent cells to regulate gene expression.…”