Gray mold, caused by Botrytis cinerea, is one of the most destructive diseases of grapevine and is controlled with an intense application of fungicides. As alternatives to chemicals, beneficial microbes may promote plant health by stimulating the plant’s immune system. An actinomycete, Streptomyces anulatus S37, has been screened from the rhizosphere microbiome of healthy Vitis vinifera on the basis of its ability to promote grapevine growth and to induce resistance against various phytopathogens, including B. cinerea. However, molecular mechanisms involved locally after direct perception of these bacteria by plant cells still remain unknown. This study focuses on local defense events induced in grapevine cells during interactions with S. anulatus S37 before and after pathogen challenge. We demonstrated that S. anulatus S37 induced early responses including oxidative burst, extracellular alkalinization, activation of protein kinases, induction of defense gene expression and phytoalexin accumulation, but not the programmed cell death. Interestingly, upon challenge with the B. cinerea, the S. anulatus S37 primed grapevine cells for enhanced defense reactions with a decline in cell death. In the presence of the EGTA, a calcium channel inhibitor, the induced oxidative burst, and the protein kinase activity were inhibited, but not the extracellular alkalinization, suggesting that Ca2+ may also contribute upstream to the induced defenses. Moreover, desensitization assays using extracellular pH showed that once increased by S. anulatus S37, cells became refractory to further stimulation by B. cinerea, suggesting that grapevine cells perceive distinctly beneficial and pathogenic microbes.

Plant growth and survival depends critically on photo assimilates. Pathogen infection leads to changes in carbohydrate metabolism of plants. In this study, we monitored changes in the carbohydrate metabolism in the grapevine inflorescence and leaves using Botrytis cinerea and Botrytis pseudo cinerea. Fluctuations in gas exchange were correlated with variations in chlorophyll a fluorescence. During infection, the inflorescences showed an increase in net photosynthesis (Pn) with a stomatal limitation. In leaves, photosynthesis decreased, with a non-stomatal limitation. A decrease in the effective photosystem II (PSII) quantum yield (ΦPSII) was accompanied by an increase in photochemical quenching (qP) and non-photochemical quenching (qN). The enhancement of qP and ΦPSII could explain the observed increase in Pn. In leaves, the significant decline in ΦPSII and qP, and increase in qN suggest that energy was mostly oriented toward heat dissipation instead of CO2 fixation. The accumulation of glucose and sucrose in inflorescences and glucose and fructose in the leaves during infection indicate that the plant's carbon metabolism is differently regulated in these two organs. While a strong accumulation of starch was observed at 24 and 48 hours post-inoculation (hpi) with both species of Botrytis in the inflorescences, a significant decrease with B. cinerea at 24 hpi and a significant increase with B. pseudo cinerea at 48 hpi were observed in the leaves. On the basis of these results, it can be said that during pathogen attack, the metabolism of grapevine inflorescence and leaf is modified suggesting distinct mechanisms modifying gas exchange, PSII activity and sugar contents in these two organs.