Bacterial RNAs activate innate immunity in Arabidopsis

Abstract

Summary The common molecular patterns of microbes play a critical role in the regulation of plant innate immunity. However, little is known about the role of nucleic acids in this process in plants. We pre‐infiltrated Arabidopsis leaves with total RNAs from Pseudomonas syringae pv. tomato DC3000 (Pto DC3000) and subsequently inoculated these plants with the same bacterial cells. Total Pto DC3000 RNAs pre‐infiltrated into Arabidopsis leaves elicited plant immune responses against Pto DC3000. However, sheared RNAs and RNase A application failed to induce immunity, suggesting that intact bacterial RNAs function in plant innate immunity. This notion was supported by the positive regulation of superoxide anion levels, callose deposition, two mitogen‐activated protein kinases and defense‐related genes observed in bacterial RNA‐pre‐treated leaves. Intriguingly, the Pto DC3000 population was not compromised in known pattern recognition receptor mutants for chitin, flagellin and elongation factor‐Tu (EF‐Tu). Plant defense‐related mutant analyses further revealed that bacterial RNA‐elicited innate immunity was normally required for salicylic and jasmonic acid signaling. Notably, among total RNAs, the abundant bacterial RNA species 16S and 23S ribosomal RNAs were the major determinants of this response. Our findings provide evidence that bacterial RNA serves as a microbe‐associated molecular pattern in plants.

Transient Expression of Whitefly Effectors in Nicotiana benthamiana Leaves Activates Systemic Immunity Against the Leaf Pathogen Pseudomonas syringae and Soil-Borne Pathogen Ralstonia solanacearum

“…Besides protein effectors, non-protein salivary factors can also act as effectors (Su et al, 2015). Bacterial rRNAs and plant DNA were recently shown to elicit SAR (Bhat and Ryu, 2016;Lee et al, 2016). Destroying the structure of bacterial rRNA via sonication and RNase treatment greatly reduced its effect on inducing SAR, indicating that certain (structural or sequence) signatures of rRNA are required for full SAR elicitation.…”

Getting to PTI of bacterial RNAs: Triggering plant innate immunity by extracellular RNAs from bacteria

“…Foreign non-self signals or molecular patterns are perceived by pattern recognition receptors (PRRs) in plants 6 leaves. The pathogen population was 10-fold higher in leaves treated with RNase A + bacterial RNAs than in those treated with bacterial RNAs alone 11 . In addition, 5-fold more pathogen colonies were observed in leaves treated with bacterial RNAs + proteinase K than in those treated with bacterial RNAs alone 11 .…”

“…The pathogen population was 10-fold higher in leaves treated with RNase A + bacterial RNAs than in those treated with bacterial RNAs alone 11 . In addition, 5-fold more pathogen colonies were observed in leaves treated with bacterial RNAs + proteinase K than in those treated with bacterial RNAs alone 11 . These results clearly demonstrate that bacterial RNAs are indeed implicated in the modulation of innate immunity in Arabidopsis.…”

“…It is possible that the activity of RNase A and proteinase K was not completely diminished during the pre-incubation process and that the residual activity affected the pathogen population density. 11 . A result of our study concerning plant defense signaling pathways differs from that of a previous study.…”

“…However, little is known about the effects of nucleic acids on innate immunity in plants. To shed light on the functions of nucleic acids in this process in Arabidopsis RNA, suggesting that the host plant can recognize bacterial RNAs as a "non-self" signaling molecule11 . However, this suggestion can be countered by the fact that bacterial RNAs are structurally similar to plant ATP 12 .…”