Pattern triggered immunity (PTI) in tobacco: isolation of activated genes suggests role of the phenylpropanoid pathway in inhibition of bacterial pathogens.

Ágnes Szatmári,Eszter Besenyei,Ágnes M Móricz,Zoltán Bozsó,László G Puskás,Erika Szabó,Péter G Ott,Ágnes Zvara,Boris Alexander Vinatzer

doi:10.1371/journal.pone.0102869

Abstract

BackgroundPattern Triggered Immunity (PTI) or Basal Resistance (BR) is a potent, symptomless form of plant resistance. Upon inoculation of a plant with non-pathogens or pathogenicity-mutant bacteria, the induced PTI will prevent bacterial proliferation. Developed PTI is also able to protect the plant from disease or HR (Hypersensitive Response) after a challenging infection with pathogenic bacteria. Our aim was to reveal those PTI-related genes of tobacco (Nicotiana tabacum) that could possibly play a role in the protection of the plant from disease.Methodology/Principal FindingsLeaves were infiltrated with Pseudomonas syringae pv. syringae hrcC- mutant bacteria to induce PTI, and samples were taken 6 and 48 hours later. Subtraction Suppressive Hybridization (SSH) resulted in 156 PTI-activated genes. A cDNA microarray was generated from the SSH clone library. Analysis of hybridization data showed that in the early (6 hpi) phase of PTI, among others, genes of peroxidases, signalling elements, heat shock proteins and secondary metabolites were upregulated, while at the late phase (48 hpi) the group of proteolysis genes was newly activated. Microarray data were verified by real time RT-PCR analysis. Almost all members of the phenyl-propanoid pathway (PPP) possibly leading to lignin biosynthesis were activated. Specific inhibition of cinnamic-acid-4-hydroxylase (C4H), rate limiting enzyme of the PPP, decreased the strength of PTI - as shown by the HR-inhibition and electrolyte leakage tests. Quantification of cinnamate and p-coumarate by thin-layer chromatography (TLC)-densitometry supported specific changes in the levels of these metabolites upon elicitation of PTI.Conclusions/SignificanceWe believe to provide first report on PTI-related changes in the levels of these PPP metabolites. Results implicated an actual role of the upregulation of the phenylpropanoid pathway in the inhibition of bacterial pathogenic activity during PTI.

Highlights

Pattern Triggered Immunity (PTI), known as Basal Resistance (BR) is a general form of defense that plants use to maintain their integrity by detecting and eradicating almost any type of invading organism, including non-pathogens
For this purpose one half of the tobacco leaves was treated with a 108 CFU/ml suspension of P. syringe hrcC mutant bacteria, while the other half served as a control
The first two indicator genes seem to be specific for leguminous PTI, as they are activated in Medicago as well [34] but not in Arabidopsis [4] and tobacco (Szatmari et al unpublished)

Summary

Introduction

Pattern Triggered Immunity (PTI), known as Basal Resistance (BR) is a general form of defense that plants use to maintain their integrity by detecting and eradicating almost any type of invading organism, including non-pathogens. Effector Triggered Immunity (ETI), known as gene-for-gene resistance of plants, on the other hand requires detection of specific effector proteins of pathogens by plant R-gene products, which eventually leads to the hypersensitive reaction (HR) of plant cells and eradication of that specific pathogen. This manuscript focuses on molecular changes in plant cells during PTI. Our aim was to reveal those PTI-related genes of tobacco (Nicotiana tabacum) that could possibly play a role in the protection of the plant from disease

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