Mature grapevine berries at the harvesting stage (MB) are very susceptible to the grey mould fungus Botrytis cinerea while veraison berries (VB) are not. We conducted simultaneous microscopic and transcriptomic analyses of the pathogen and the host to investigate the infectious process developed by B. cinerea on MB versus VB, and the plant defence mechanisms deployed to stop the fungus development. On the pathogen side, our genome-wide transcriptomic data revealed that B. cinerea genes up-regulated during infection of MB are enriched in functional categories related to necrotrophy such as degradation of plant cell wall, proteolysis, membrane transport, oxidative stress response and secondary metabolism. Quantitative-PCR on a set of representative genes and microscopic observations further demonstrated that the infection is similarly initiated on VB but stops at the penetration stage. This suggested that the berry defence mechanisms are the “major determinants” of the infection success or failure. On the plant side, we therefore compared the transcriptomes of the infected VB versus MB which revealed that the defence pathways clearly switch during berry ripening. In particular, differences were revealed regarding salicylate and jasmonate hormones, burst of reactive oxygen species (ROS), secondary phenylpropanoid products such as phytoalexin and lignin compounds involved in cell-wall strengthening.Read less <