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Impact de la nutrition azotée sur l'interaction entre Arabidopsis thaliana et la bactérie phytopathogène Erwinia amylovora

Abstract : Nitrogen (N) is one of the key nutrients needed for plant growth and crop yield. It is well documented that changes in the availability of nitrate, the main source of nitrogen in agricultural soils, greatly influence the process of plant development, including its defense responses.The first part of this work corresponds to a transcriptomic analysis, carried out in order to study the transcriptional changes during the infection of A. thaliana by E. amylovora, in plants grown under two nitrogen nutrition regimes (limiting or not). Analysis of the data shows that, generally, the transcriptomic response to the bacterium in plants grown in nitrogen limiting or not is close despite the difference in development of these plants. Despite these broadly similar responses, differences in expression in response to infection have been observed for some signaling pathways, notably for the jasmonic acid pathway. Analysis of the interaction between the two stresses (N and bacteria) shows that in response to the combination of the two stresses, 32.5% of genes have a specific response to stress combination, suggesting an interaction between simple stress responses. Among these genes, several are linked to defense against pathogens, such as WRKY transcription factors and resistance proteins.In the second part of this work, we demonstrated the effect of nitrogen availability on the expression of E. amylovora pathogenicity factors in planta. Indeed, bacteria multiplicated more in plants grown in low nitrogen (2 mM NO3⁻) than high nitrogen (10 mM NO3⁻). In addition, we only observed that mutant affected in the pathogenicity of E. amylovora is as aggressive as the wild-type strain in plants grown in high nitrogen (10 mM NO3⁻), while there is a difference in aggressiveness between the two strains in plants grown in low nitrogen (2 mM NO3⁻). The experiments indicate that the DspA / E effector, the main factor in the pathogenicity of E. amylovora, is significantly more expressed in planta at low nitrogen (2 mM NO3⁻) than at high nitrogen (10 mM NO3⁻). In addition, the level of expression of this virulence factor of E. amylovora in planta is inversely correlated with gene expression of the jasmonic acid pathway PDF1.2 and JAR1. Out results showed also a decrease in the level of chloroplastic precursors of jasmonic acid in susceptible plants to Ea grown in low N.
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Mahsa Farjad. Impact de la nutrition azotée sur l'interaction entre Arabidopsis thaliana et la bactérie phytopathogène Erwinia amylovora. Phytopathologie et phytopharmacie. Université Paris Saclay (COmUE), 2017. Français. ⟨NNT : 2017SACLS215⟩. ⟨tel-01885495⟩

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