ABSTRACT
In Arabidopsis thaliana, responses to pathogen-associated molecular patterns (PAMPs) are mediated by cell surface pattern recognition receptors (PRRs) and include the accumulation of reactive oxygen species, callose deposition in the cell wall, and the generation of the signal molecule salicylic acid (SA). SA acts in a positive feedback loop with ACCELERATED CELL DEATH6 (ACD6), a membrane protein that contributes to immunity. This work shows that PRRs associate with and are part of the ACD6/SA feedback loop. ACD6 positively regulates the abundance of several PRRs and affects the responsiveness of plants to two PAMPs. SA accumulation also causes increased levels of PRRs and potentiates the responsiveness of plants to PAMPs. Finally, SA induces PRR- and ACD6-dependent signaling to induce callose deposition independent of the presence of PAMPs. This PAMP-independent effect of SA causes a transient reduction of PRRs and ACD6-dependent reduced responsiveness to PAMPs. Thus, SA has a dynamic effect on the regulation and function of PRRs. Within a few hours, SA signaling promotes defenses and downregulates PRRs, whereas later (within 24 to 48 h) SA signaling upregulates PRRs, and plants are rendered more responsive to PAMPs. These results implicate multiple modes of signaling for PRRs in response to PAMPs and SA.
Subject(s)
Ankyrins/metabolism , Arabidopsis Proteins/metabolism , Arabidopsis/metabolism , Protein Kinases/metabolism , Protein Serine-Threonine Kinases/metabolism , Salicylic Acid/metabolism , Ankyrins/genetics , Arabidopsis/genetics , Arabidopsis/microbiology , Arabidopsis Proteins/genetics , Flagellin/pharmacology , Gene Expression Regulation, Plant , Glucans/metabolism , Host-Pathogen Interactions , Immunoblotting , Mitogen-Activated Protein Kinases/genetics , Mitogen-Activated Protein Kinases/metabolism , Mutation , Protein Binding/drug effects , Protein Kinases/genetics , Protein Serine-Threonine Kinases/genetics , Pseudomonas syringae/physiology , Reactive Oxygen Species/metabolism , Receptors, Pattern Recognition/genetics , Receptors, Pattern Recognition/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Salicylic Acid/agonists , Signal Transduction/drug effects , Signal Transduction/genetics , Thiadiazoles/pharmacologyABSTRACT
BACKGROUND: Tomato yellow leaf curl virus disease (TYLCVD) causes severe to economic losses in tomato crops in China. The control of TYLCVD is based primarily on the use of synthetic insecticide to control its vector whitefly (Bemisia tabaci). To look for an alternative method for disease control, we investigated the effect of eugenol on controlling TYLCVD. The potential of eugenol to trigger systemic acquired resistance (SAR) in tomato (Jiangsu 14) plants against TYLCV was also investigated. RESULTS: In greenhouse experiments, eugenol significantly reduced disease severity when applied as a foliar spray, thus demonstrating a systemic effect. The disease spread rapidly in control plants and by the end of the experiment almost all control plants showed severe symptoms. Eugenol also induced H2O2 accumulation in tomato plants. Activities of peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) were significantly induced compared with those of control plants. As further consequences, increase of salicylic acid (SA) levels and expression of PR-1 proteins, a molecular marker of SAR in tomato, could also be observed. CONCLUSION: This is the first report of eugenol as an elicitor and its ability to suppress plant virus diseases under greenhouse conditions. It is suggested that eugenol has the potential to be an effective biocontrol agent against TYLCV in tomato plants.
Subject(s)
Anti-Infective Agents/pharmacology , Begomovirus/immunology , Disease Resistance/drug effects , Eugenol/pharmacology , Plant Diseases/prevention & control , Solanum lycopersicum/drug effects , Aerosols , Anti-Infective Agents/administration & dosage , Begomovirus/growth & development , Catechol Oxidase/chemistry , Catechol Oxidase/metabolism , China , Enzyme Induction/drug effects , Eugenol/administration & dosage , Hydrogen Peroxide/metabolism , Isoenzymes/chemistry , Isoenzymes/metabolism , Solanum lycopersicum/immunology , Solanum lycopersicum/metabolism , Solanum lycopersicum/virology , Peroxidase/chemistry , Peroxidase/metabolism , Phenylalanine Ammonia-Lyase/chemistry , Phenylalanine Ammonia-Lyase/metabolism , Plant Diseases/immunology , Plant Diseases/virology , Plant Leaves/drug effects , Plant Leaves/immunology , Plant Leaves/metabolism , Plant Leaves/virology , Plant Proteins/agonists , Plant Proteins/metabolism , Salicylic Acid/agonists , Salicylic Acid/metabolism , Up-Regulation/drug effectsABSTRACT
Plant activators are agrochemicals that protect crops from pathogens. They confer durable resistance to a broad range of diseases by activating intrinsic immune mechanisms in plants. To obtain leads regarding useful compounds, we have screened a chemical library using an established method that allows selective identification of immune-priming compounds. Here, we report the characterisation of one of the isolated chemicals, imprimatinC1, and its structural derivative imprimatinC2. ImprimatinC1 functions as a weak analogue of salicylic acid (SA) and activates the expression of defence-related genes. However, it lacks antagonistic activity toward jasmonic acid. Structure-activity relationship analysis suggests that imprimatinC1 and C2 can be metabolised to 4-chlorobenzoic acid and 3,4-chlorobenzoic acid, respectively, to function in Arabidopsis. We also found that imprimatinC1 and C2 and their potential functional metabolites acted as partial agonists of SA. Thus, imprimatinC compounds could be useful tools for dissecting SA-dependent signal transduction pathways.
