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See detailInvolvement of the lipoxygenase pathway in the systemic resistance induced by Plant Growth-Promoting Rhizobacteria in tomato
Mariutto, Martin ULg

Doctoral thesis (2013)

The treatment of plant roots with some Plant Growth Promoting Rhizobacteria (PGPR) results in the enhancement of the immune capacity of the host against phytopathogens. This phenomenon called Induced ... [more ▼]

The treatment of plant roots with some Plant Growth Promoting Rhizobacteria (PGPR) results in the enhancement of the immune capacity of the host against phytopathogens. This phenomenon called Induced Systemic Resistance (ISR) is observed in the whole plant and is effective against a broad spectrum of diseases. Many previous studies showed that this resistance is associated, in some pathosystems, with the stimulation of the key enzyme of the lipoxygenase (LOX) pathway. This defense pathway synthesizes antibiotic and signal compounds called oxylipins from poly unsaturated fatty acids. The main goal of our work was to analyse the involvement of the LOX pathway during the ISR in tomato plants The different steps of the pathway were analyzed at the transcriptional, enzymatic and metabolic levels in leaves of tomato plants elicited with the PGPR Pseudomonas putida BTP1, before and after infection by the fungal pathogen Botrytis cinerea. Our study showed that the bacterial treatment reprogrammed the LOX pathway. Before infection, the activity of the key enzyme of the pathway, the LOX, was higher in P. putida BTP1-treated plants compared to control plants. This stimulation resulted in the accumulation 13-hydroperoxy fatty acids and 13-hydroxyfatty acids conjugated to phospholipids and galactolipids. These products could constitute a pool of antifungal compounds that can be used during the pathogen attack. During the first days after B. cinerea inoculation, the LOX activity, the accumulation of one of its substrate (linolenic acid) and of its products were stimulated in treated plants as compared to control plants. The increase of LOX activity was caused by the induction of the expression level of two Lox genes: TomLoxD and TomLoxF. We observed a decrease of the pool of conjugated oxylipins and a concomitant increase of non conjugated oxylipins, associated with the stimulation of the phospholipase A2 activity. The branches of the pathway which can use the products of the LOX as substrate were differentially regulated resulting in the accumulation of fungitoxic oxylipins against B. cinerea. In order to determine if the induction of the LOX pathway is a general feature of the ISR in tomato, the effect of other PGPR and resistance elicitors produced by PGPR was analysed. Three pure bacterial elicitors sharing common biosurfactant features (the n-alkylated benzylamine derivative (NABD) produced by P. putida BTP1, the surfactin synthesized by many Bacillus strains and rhamnolipids purified from P. aeruginosa) and six Bacillus strains including strong, medium and non producers of surfactin were applied onto tomato roots. The analysis of the key points of the modulation of the LOX pathway showed that the plant molecular response depended on the studied organ (root / leaf), the nature of the elicitor and the amount of elicitor produced by the PGPR. In addition to our study on the involvement of the LOX pathway, we searched other mechanisms potentially induced in ISR-expressing plants. The combination of histological staining, quantification of enzymatic activities and analysis of the genome expression by hybridization on DNA gene chips showed additional defense genes and pathways involved in the resistance in tomato. In conclusion, our work showed that the LOX pathway is one of the defense mechanisms which can be involved in ISR in tomato. The elicitation of the resistance allows the plant to prepare to a future infection, and to respond faster and in a more effective way to a subsequent pathogen invasion. [less ▲]

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See detailThe elicitation of a systemic resistance by Pseudomonas putida BTP1 in tomato involves the stimulation of two lipoxygenase isoforms
Mariutto, Martin ULg; Duby, Franceline ULg; Adam, Akram et al

in BMC Plant Biology (2011), 11

Background Some non-pathogenic rhizobacteria called Plant Growth Promoting Rhizobacteria (PGPR) possess the capacity to induce in plant defense mechanisms effective against pathogens. Precedent studies ... [more ▼]

Background Some non-pathogenic rhizobacteria called Plant Growth Promoting Rhizobacteria (PGPR) possess the capacity to induce in plant defense mechanisms effective against pathogens. Precedent studies showed the ability of Pseudomonas putida BTP1 to induce PGPR-mediated resistance, termed ISR (Induced Systemic Resistance), in different plant species. Despite extensive works, molecular defense mechanisms involved in ISR are less well understood that in the case of pathogen induced systemic acquired resistance. Results We analyzed the activities of phenylalanine ammonia-lyase (PAL) and lipoxygenase (LOX), key enzymes of the phenylpropanoid and oxylipin pathways respectively, in tomato treated or not with P. putida BTP1. The bacterial treatment did not stimulate PAL activity and linoleate-consuming LOX activities. Linolenate-consuming LOX activity, on the contrary, was significantly stimulated in P. putida BTP1-inoculated plants before and two days after infection by B. cinerea. This stimulation is due to the increase of transcription level of two isoforms of LOX: TomLoxD and TomLoxF, a newly identified LOX gene. We showed that recombinant TomLOXF preferentially consumes linolenic acid and produces 13-derivative of fatty acids. After challenging with B. cinerea, the increase of transcription of these two LOX genes and higher linolenic acid-consuming LOX activity were associated with a more rapid accumulation of free 13-hydroperoxy-octadecatrienoic and 13-hydroxy-octadecatrienoic acids, two antifungal oxylipins, in bacterized plants. Conclusion In addition to the discovery of a new LOX gene in tomato, this work is the first to show differential induction of LOX isozymes and a more rapid accumulation of 13-hydroperoxy-octadecatrienoic and 13-hydroxy-octadecatrienoic acids in rhizobacteria mediated-induced systemic resistance. [less ▲]

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See detailIdentification, characterization and expression profiling of the tomato gene TomLoxF
Mariutto, Martin ULg; Duby, Franceline ULg; Adam, Akram et al

Poster (2010, January 26)

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See detailThe mechanisms for plant growth promotion by PGPRs
Mariutto, Martin ULg

Scientific conference (2009, April 02)

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See detailModulation de la voie de la lipoxygénase dans le cadre de la résistance systémique induite chez la tomate
Mariutto, Martin ULg

Master of advanced studies dissertation (2008)

Detailed reference viewed: 11 (2 ULg)