Pattern Triggered Immunity (PTI) in Tobacco: Isolation of Activated Genes Suggests Role of the Phenylpropanoid Pathway in Inhibition of Bacterial Pathogens

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.

Overlapping Yet Response-Specific Transcriptome Alterations Characterize the Nature of Tobacco–Pseudomonas syringae Interactions

“…Leaf materials were collected at 6 h after inoculations (6 hpi). This sampling time was chosen on the basis of our previous work since PTI develops in tobacco by this time at 20°C as detected by using various marker reactions (Burgyán and Klement, 1979 ; Ott et al, 1997 , 2006 ; Bozsó et al, 1999 , 2005 ; Klement et al, 1999 , 2003 ; Szatmári et al, 2006 , 2014 ).…”

“…A typical response during both PTI and ETI at 6 hpi was the activation of phenylpropanoid/phenolics synthesis genes, especially those of lignin biosynthesis, which is characteristic of PTI-associated cell wall strengthening responses (Table S4 ). The accumulation of phenylpropanoid compounds is a common plant response after bacterial infection (Bestwick et al, 1995 ; Szatmári et al, 2014 ). Interestingly, the activity of some of these phenylpropanoid biosynthesis genes are retained even at a later phase of PTI (48 hpi), suggesting the importance of sustained lignin synthesis during PTI.…”

Defining essential processes in plant pathogenesis with Pseudomonas syringae pv. tomato DC3000 disarmed polymutants and a subset of key type III effectors

“…However, RNA‐seq transcription profiling aimed at distinguishing PTI and ETI responses of tomato to DC3000 derivatives revealed enrichment for genes associated with the phenylpropanoid pathway in the PTI‐specific set (Pombo et al ., ). Phenylpropanoid pathway genes were similarly found in a transcriptome study of PTI genes in tobacco (Szatmari et al ., ), and the N. benthamiana VIGS screen identified the CA4H gene which plays a role in phenylpropanoid biosynthesis (Chakravarthy et al ., ). Histochemical study of a DC3000 T3SS – mutant in Arabidopsis highlighted the localized production of H 2 O 2 by chloroplasts as a prominent response that could promote plant cell wall strengthening and bacterial agglutination (Mitchell et al ., ).…”

Differential Regulation of Maize and Sorghum Orthologs in Response to the Fungal Pathogen Exserohilum turcicum

“…During the incompatible interaction at 72 hai, DEOs were related to pathogen reception, signal transduction, and the defense response ( Supplementary Table 7 ). Several of the DEOs are either a part of pathogen associated molecular pattern (PAMP)-triggered immunity (PTI), or were activated in PTI-induced leaves in previous studies ( Szatmari et al, 2014 ; Bozso et al, 2016 ). Additionally, an orthologous gene pair encoding a potassium transporter ( kup1/Sobic.003G413700 ; involved in potassium mobilization), a serine carboxypeptidase ( LOC100281606/Sobic.003G081100 ; function as acyltransferase), a lactate/malate dehydrogenase ( LOC103632470/Sobic.001G471100 ; involved in carboxylic metabolic pathway and oxidation-reduction process), and several orthologous gene pairs encoding cytochrome P450s (involved in biosynthetic and detoxification pathway) were upregulated in both crops ( Supplementary Table 7 ).…”