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National audience; Les invasions biologiques sont souvent la source d’émergences nouvelles de maladies, et le résultat d’activités humaines et des changements globaux (e.g. changements climatiques, d’échanges commerciaux, d’occupation des terres, de pratiques phytosanitaires). C’est particulièrement vrai historiquement pour les vignobles français et bordelais, pour lesquels la plupart des ravageurs, vecteurs ou maladies de la vigne, ont été le résultat d’introductions plus ou moins récentes. Le projet RIVA (Risques d’Invasions en Vignobles Aquitain) vise à optimiser la mise en place de programmes d’épidémio-surveillance en 2015 et 2016, sur la partie sud du vignoble bordelais, région du Sauternais et des Graves. Son objectif était de détecter l’apparition ou la progression d'espèces invasives d'insectes ravageurs et vecteurs, en se focalisant sur des espèces à forts potentiels de risques pour la viticulture. Basé sur deux campagnes de surveillance menées dans la partie sud du vignoble bordelais (i.e., région du Sauternais) et à l’aide de différentes techniques de piégeage, ce projet s’est intéressé à la surveillance de différentes espèces : les espèces vectrices de la Flavescence dorée (Scaphoideus titanus et Orientus ishidae), la drosophile japonaise (Drosophila suzukii) et la mouche africaine de la figue (Zaprionus indianus), le fulgore du stolbur (Hyalesthes obsoletus) et différentes espèces de Cixiidae potentiellement vectrices du phytoplasme du bois noir, une chenille de papillon mineuse de feuilles introduite en 2006 en Italie (Antispila oinophylla), et les vecteurs potentiels de la maladie de Pierce (Xyllela fastidiosa). Les deux années de campagne ont permis d’identifier une large diversité de cicadelles avec 73 espèces collectées en 2015 et 78 en 2016. Nos résultats ont également mis en évidence la présence chronique d’O. ishidae sur certaines parcelles surveillées et ont confirmé que des proportions non négligeables d’individus capturés étaient porteuses d’une des souches du phytoplasme responsable de la Flavescence dorée.

National audience

National audience

International audience; DNA methylation was investigated as a possible mechanism for regulation of floral gene expression in stolbur phytoplasma-infected tomato buds. Expression of methylase and demethylase genes was found to be globally down-regulated in tomato plants infected with stolbur isolate PO, but not in those infected with isolate C. These results are consistent with the finding that SlDEF, a gene orthologous to arabidopsis APETALA3 which is involved in petal formation, was down-regulated in stolbur PO-infected buds and remained unaffected in stolbur C-infected buds, and with the fact that the two stolbur phytoplasma isolates C and PO induce distinct symptoms. Because of variations between the different cell-types of the flower buds, the DNA methylation status of SlDEF could not be clearly established. However, the finding that treatment of stolbur PO-infected plants with 5-azacytidine partially restored SlDEF gene expression strongly suggests that DNA methylation is involved in down-regulation of floral development genes in stolbur PO-infected tomatoes.

National audience

National audience

International audience; A report describing the strong resistance and tolerance of the accession PI128655 of Solanum peruvianum to two BLTVA strains (beet leafhopper transmitted virescence agent; `Candidatus Phytoplasma trifolii') was published almost twenty years ago. This work was revisited using another BLTVA strain and the PI128655 plants. No resistance or tolerance was observed. Instead the plants showed either one of two different sets of symptoms. A genetic control of the response to the phytoplasma isolated by the PI128655 plants was demonstrated using clones of host plants. However we obtained experimental evidence that the BLTVA isolate lacked homogeneity or stability, which could also explain the occurrence of two sets of symptoms. A possible hypothesis is that the PI128655 plants, by interfering with the competition between the 'components' of the BLTVA isolate, can alter the final composition of the phytoplasma population and therefore influence the induced symptoms.

National audience

National audience

Salicylic acid (SA) is an important mediator of plant defense response. In Arabidopsis thaliana, this compound was proposed to derive mainly from isochorismate, itself produced from chorismate through the activity of ICS1 (Isochorismate Synthase1). Null ics1 mutants still accumulate some SA, suggesting the existence of an enzymatic activity redundant with ICS1 or of an alternative ICS-independent SA biosynthetic route. Here we studied the role of ICS2, second ICS gene of the Arabidopsis genome, in the production of SA. We have shown that ICS2 encodes a functional ICS enzyme and that, similarly to ICS1, ICS2 is targeted to the plastids. Comparison of SA accumulation in the ics1, ics2 and ics1 ics2 mutants indicates that ICS2 participates in the synthesis of SA but in limited amounts, that become clearly detectable only when ICS1 is lacking. This unequal redundancy relationship was also observed for phylloquinone, another isochorismate-derived end-product. Furthermore, detection of SA in the double ics1 ics2 double mutant that is completely devoid of phylloquinone provides genetic evidence of the existence of an ICS-independent SA biosynthetic pathway in Arabidopsis.

FiRe is a user-friendly Excel® macro designed to survey microarray data rapidly. This software interactively assembles data from different experiments and produces lists of candidate genes according to patterns of gene expression. Furthermore, macros bundled with FiRe can compare lists of genes, merge information from different spreadsheets, link candidates to information available from web-based databases, and produce heat-maps for easy visualization of microarray data. FiRe is freely available at http://www.unifr.ch/plantbio/FiRe/main.html.