Bacterium-induced basal resistance inhibits viral infection in tobacco plants László ZSIROS 1,2, Ágnes SZATMÁRI 1, László PALKOVICS 2, Zoltán KLEMENT 1 Zoltán BOZSÓ 1 1 Plant Protection Institute of the HAS 2 Corvinus University of Budapest Dept. of Plant Pathology

Main types of resistance in plants Preformed Microorganism-induced Hypersensitive response (HR) Basal resistance (BR) Early basal resistance (EBR) Late basal resistance (LBR)

Comparison of basal and hypersensitive defense Type of resistanceHypersensitiveBasal Plant-bacterium interaction SpecificNon-specific Inducer bacteriumMetabolically active pathogen Pathogen, saprotroph, heat killed, etc. SymptomCell necrosisSymptomless (detection with superinfection)

Induction of basal resistance (BR) and hypersensitive response (HR) Plant cell Basal resistance Flagellin, LPS Avr proteins Hypersensitive response Intercellular space

Tobacco mosaic virus (TMV) Resistance in tobacco HR – 78 hours N gene Plant-TMV interaction incompatible (HR) compatible (mosaic leaves)

Changes at cell level during basal resistance (BR) change in pH level cell wall fortification papilla formation active oxygen forms (eg. hydrogen peroxide) bacterium envelopment

Aims of research Does a bacterial infection impede the symptoms/HR of a viral superinfection? Is symptom/HR inhibition attached to bated virus replication? How do some defense-related genes change in their transcription activity?

Materials and methods Plants –N. tabacum L. ‘Samsun’ nn (compatible) –N. tabacum L. ‘Xanthi’ NN (incompatible) Bacterial inoculation –Pseudomonas syringae pv. syringae hrcC mutant Viral inoculation –TMV Virus quantity and gene activity assay –Real-Time PCR

Inoculation method to assay early basal resistance (EBR) Bacterial inoculation Water infiltration (mock) Viral inoculation 6 hours TMV

HR-inhibition assay (‘Xanthi’ NN plant, incompatible tobacco-TMV interaction) Bacterium (hrcC) + TMV Water + TMV Positive control (TMV only)

HR-inhibition assay (‘Xanthi’ NN plant, incombatible tobacco – TMV interaction) PlantPre-treatmentNumber of lesions Size of lesions Positive control (TMV only) mm Early basal resistance Water mm Bacterium671 mm Average results of repeated treatments

Inhibition of virus replication (‘Xanthi’ NN plant, incombatible tobacco – TMV interaction) Representative results of repeated treatments hrcC = Pseudomonas syringae pv. syringae hrcC mutáns

Defense-related genes (‘Xanthi’ NN plant, incompatible tobacco – TMV interaction) Epoxide hydrolase – epoxide neutralization Ortho-methyl trasferase – cell wall synthesis Superoxide dismutase – superoxide degradation

Defense-related genes 1 (‘Xanthi’ NN plant, incompatible tobacco – TMV interaction) Representative results of repeated treatments hrcC = Pseudomonas syringae pv. syringae hrcC mutant

Defense-related genes 2 (‘Xanthi’ NN plant, incompatible tobacco – TMV interaction) Representative results of repeated treatments hrcC = Pseudomonas syringae pv. syringae hrcC mutant

Defense-related genes 3 (‘Xanthi’ NN plant, incompatible tobacco – TMV interaction) Representative results of repeated treatments hrcC = Pseudomonas syringae pv. syringae hrcC mutant

Symptom inhibition of EBR (‘Samsun’ nn plant, compatible tobacco – TMV interaction) Water + TMVBacterium + TMVTMV

Inhibition of virus replication (‘Samsun’ nn plant, compatible tobacco – TMV interaction) Representative results of repeated treatments hrcC = Pseudomonas syringae pv. syringae hrcC mutant

Summary Related to EBR, there was inhibition observed in –mosaic leaf symptom development; –virus-induced HR development; –the rate of virus replication; –change in activity of some defense-related genes

Conclusions Possible reasons for HR or mosaic symptom inhibition during basal resistance: –blocking of virus translocation in plant –inhibition of virus replication (RNA silencing? priming?) –non-specific defense –hydrogen peroxide  symptoms