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Joëlle Fournier

Publications and source records attributed to Joëlle Fournier.

4 recordsLinked to original sources
PubMed2006

Characterization of a divinyl ether biosynthetic pathway specifically associated with pathogenesis in tobacco.

In tobacco (Nicotiana tabacum), an elicitor- and pathogen-induced 9-lipoxygenase (LOX) gene, NtLOX1, is essential for full resistance to pathogens, notably to an incompatible race of Phytophthora parasitica var. nicotianae (Ppn race 0). In this work, we aimed to identify those oxylipins induced during attempted infection by Ppn race 0 and down-regulated in NtLOX1 antisense plants. Here we show that colneleic and colnelenic acids, which significantly inhibit germination of Ppn zoospores, are produced in roots of wild-type plants inoculated with Ppn, but are down-regulated in NtLOX1 antisense plants. A search for a tobacco gene encoding the enzyme involved in the formation of these divinyl ether (DVE) fatty acids resulted in the cloning and characterization of a DVE synthase (DES) clone (NtDES1). NtDES1 is a 9-DES, specifically converting fatty acid 9-hydroperoxides into DVE fatty acids. NtDES1 has the potential to act in combination with NtLOX1 because, in the presence of the two enzymes, linoleic and linolenic acids were converted in vitro into colneleic and colnelenic acids, respectively. In addition, the pattern of NtDES1 gene expression was quite similar to that of NtLOX1. Their transcripts were undetected in healthy tissues from different plant organs, and accumulated locally and transiently after elicitation and fungal infection, but not after wounding. Visualization of NtDES1-yellow fluorescent protein and NtLOX1-cyan fluorescent protein fusion proteins in tobacco leaves indicated that both localize in the cytosol and are excluded from plastids, consistent with the presumed location of the 9-LOX pathway in plants and the lack of transit peptides for NtLOX1 and NtDES1, respectively. Our data suggest that, in tobacco, NtDES1 and NtLOX1 act together and form DVEs in response to pathogen attack and that this class of oxylipins modulates in vivo the outcome of the tobacco-Ppn race 0 interaction.

Cloning, Molecular↗
PubMed2005

Evaluation of the antimicrobial activities of plant oxylipins supports their involvement in defense against pathogens.

Plant oxylipins are a large family of metabolites derived from polyunsaturated fatty acids. The characterization of mutants or transgenic plants affected in the biosynthesis or perception of oxylipins has recently emphasized the role of the so-called oxylipin pathway in plant defense against pests and pathogens. In this context, presumed functions of oxylipins include direct antimicrobial effect, stimulation of plant defense gene expression, and regulation of plant cell death. However, the precise contribution of individual oxylipins to plant defense remains essentially unknown. To get a better insight into the biological activities of oxylipins, in vitro growth inhibition assays were used to investigate the direct antimicrobial activities of 43 natural oxylipins against a set of 13 plant pathogenic microorganisms including bacteria, oomycetes, and fungi. This study showed unequivocally that most oxylipins are able to impair growth of some plant microbial pathogens, with only two out of 43 oxylipins being completely inactive against all the tested organisms, and 26 oxylipins showing inhibitory activity toward at least three different microbes. Six oxylipins strongly inhibited mycelial growth and spore germination of eukaryotic microbes, including compounds that had not previously been ascribed an antimicrobial activity, such as 13-keto-9(Z),11(E),15(Z)-octadecatrienoic acid and 12-oxo-10,15(Z)-phytodienoic acid. Interestingly, this first large-scale comparative assessment of the antimicrobial effects of oxylipins reveals that regulators of plant defense responses are also the most active oxylipins against eukaryotic microorganisms, suggesting that such oxylipins might contribute to plant defense through their effects both on the plant and on pathogens, possibly through related mechanisms.

Anti-Infective Agents↗
PubMed2004

Cytological, genetic, and molecular analysis to characterize compatible and incompatible interactions between Medicago truncatula and Colletotrichum trifolii.

In this study, a new pathosystem was established using the model plant Medicago truncatula and Colletotrichum trifolii, the causal agent of anthracnose on Medicago sativa. Screening of a few M. truncatula lines identified Jemalong and F83005.5 as resistant and susceptible to Colletotrichum trifolii race 1, respectively. Symptom analysis and cytological studies indicated that resistance of Jemalong was associated with a hypersensitive response of the plant. The two selected lines were crossed, and inoculations with C. trifolii were performed on the resulting F1 and F2 progenies. Examination of the disease phenotypes indicated that resistance was dominant and was probably due to a major resistance gene. Molecular components of the resistance were analyzed through macroarray experiments. Expression profiling of 126 expressed sequence tags corresponding to 92 genes, which were selected for their putative functions in plant defense or signal transduction, were compared in Jemalong and F83005.5 lines. A strong correlation was observed between the number of up-regulated genes and the resistance phenotype. Large differences appeared at 48 h postinoculation; more than 40% of the tested genes were up-regulated in the Jemalong line compared with only 10% in the susceptible line. Interestingly, some nodulin genes were also induced in the resistant line upon inoculation with C. trifolii.

Colletotrichum↗