Bacterial RNAs activate innate immunity in Arabidopsis

• Published in: The New phytologist Vol. 209; no. 2; pp. 785 - 797
• Main Authors: Lee, Boyoung, Park, Yong‐Soon, Lee, Soohyun, Song, Geun Cheol, Ryu, Choong‐Min
• Format: Journal Article
• Language: English
• Published: England Academic Press 01-01-2016; New Phytologist Trust; Wiley Subscription Services, Inc
• Subjects: Anions; Arabidopsis; Arabidopsis - genetics; Arabidopsis - immunology; Arabidopsis - microbiology; Arabidopsis Proteins - genetics; Bacteria; bacterial RNAs; callose; Chitin; Cyclopentanes - metabolism; Electron Spin Resonance Spectroscopy; Elongation; Flagellin; Gene Expression Regulation, Plant; Genes; Immune response; Immunity; Immunity, Innate - genetics; Innate immunity; Inoculation; Jasmonic acid; jasmonic acid (JA); Kinases; Leaves; Lycopersicon esculentum; microbe‐associated molecular pattern (MAMP); Microorganisms; mitogen-activated protein kinase; Mitogen-Activated Protein Kinase Kinases - genetics; Mitogen-Activated Protein Kinases - genetics; Mutants; Nucleic acids; Oxylipins - metabolism; Pathogen-Associated Molecular Pattern Molecules - immunology; Pattern recognition; Pattern recognition receptors; Plant immunity; plant innate immunity; Plant Leaves - immunology; Plants; Pseudomonas syringae; Pseudomonas syringae - genetics; Pseudomonas syringae - pathogenicity; Pseudomonas syringae pv. tomato; ribonucleases; Ribonucleic acid; ribosomal RNA; RNA; RNA, Bacterial; RNA, Ribosomal, 16S; RNA, Ribosomal, 23S; salicylic acid; salicylic acid (SA); Salicylic Acid - metabolism; superoxide anion; Superoxide anions; Tomatoes; salicylic acid (SA); jasmonic acid (JA); Pseudomonas syringae; plant innate immunity; bacterial RNAs; microbe-associated molecular pattern (MAMP)
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.13717

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.