6533b828fe1ef96bd1287fc5

RESEARCH PRODUCT

Characterization of grapevine defense reactions and identification of elicitors : the endopolygalacturonase 1 from Botrytis cinerea, an avirulence function for a virulence factor.

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description

The fight against grapevine pathogens is mainly carried out by pesticides, the continued use of which is harmful to the environment and the health of users and consumers. The main organizations in charge of viticulture set as a priority the research and use of alternatives to chemical control. However, the genetic improvement of the vine is prohibited in AOC vineyards to preserve the varietal typicity, partly responsible for the quality of the wines. In addition, research undertaken some fifteen years ago reveals that plants have their own immune defenses, which they activate on contact with the microorganisms they recognize via molecules called elicitors. In this context, the objective of this work was both to research and identify active elicitors on grapevine, to characterize the signaling events and the defense reactions activated by these elicitors and finally to verify that the application of elicitors on grapevine could lead to increased resistance to pathogens.We have purified, from the culture filtrates of a strain of Botrytis cinerea with low virulence on grapevine, a protein elicitor which induces a set of defense reactions in cell suspensions of Vitis vinifera cv Gamay: calcium influx, efflux of nitrate, activation of two MAPKs, production of H2O2, activation of defense genes, production of phytoalexins. These results are the first to describe a set of defense reactions in grapevine. They reveal similarities but also differences with the defense mechanisms involved and identified in model plants such as tobacco. Mass spectrometry made it possible to identify this elicitor of Botrytis cinerea; it is the endopolygalacturonase 1 (BcPG1), hitherto considered as a virulence factor. This result is an original contribution to understanding the molecular dialogue between plants and microbes during evolution. Two other elicitors have proven to be effective on grapevine: laminarin, a linear polymer of beta-1,3-glucan extracted from the seaweed Laminaria digitata, and oligogalacturonates (OGs), alpha-1,4 polymers of galacturonic acid in particular produced by hydrolysis of the plant wall by endopolygalacturonases. The qualitative, quantitative and kinetics comparison of events activated by BcPG1 and OG suggested that the eliciting activity of BcPG1 did not come solely from the release of OGs via its enzymatic activity. Desensitization experiments confirmed that BcPG1 and OGs were perceived by grapevine cells as two distinct stimuli. Chemical or physical treatments of the protein made it possible to discriminate between the eliciting and enzymatic activities of BcPG1, thus showing that the eliciting activity of this protein does not come from its enzymatic activity, but probably from structural motifs specific to BcPG1 and recognized by the plant.Different protection tests have been developed to evaluate the protection of grapevine induced by elicitors against two pathogenic agents: Botrytis cinerea (the agent of grey mold) and Plasmopara viticola (the agent of downy mildew). The results show that the development of these pathogens is reduced by more than 50% when grapevine is pre-treated with elicitors. These results are very promising in the perspective of an application in reasoned viticulture.