Study of the molecular dialogue between grapevine inflorescence/berry and Botrytis cinerea during the initial, quiescent, and egression infection stages

Grapes quality and yield are affected by bunch rot disease caused by the necrotrophic fungus Botrytis cinerea. Primary infections are mostly initiated at blooming by airborne conidia but the fungus often remains quiescent from bloom until maturity when it causes bunch rot. Molecular analyses of the interaction between B. cinerea and the flower/berry of grapevine (Vitis vinifera L.) were carried out using confocal microscopy and integrated transcriptomic and metabolic analysis of the host and the pathogen. Open flowers from fruiting cuttings of the cv. Pinot Noir were infected with GFP labeled B. cinerea and samples taken at 24 and 96 hours post inoculation (hpi), 4 weeks post inoculation (wpi), and 12 wpi, were studied. Penetration of the flower epidermis by B. cinerea at 24 hpi coincided with increased expression of fungal genes encoding virulence factors and induced a rapid defense reaction in the flowers involving genes associated with the accumulation of PR proteins, stilbenoids, reactive oxygen species and cell wall reinforcement. At 96 hpi the transcriptional reaction appeared largely diminished both in the host and in the pathogen. Afterwards, infected berries continued their developmental program without any visible symptom, although the presence of B. cinerea could be ascertained. Nonetheless, at the transcriptional level, both the fungus and the hard-green berries displayed to be transcriptionally active. At 12 wpi, the egressed B. cinerea expressed almost all virulence and growth related genes to enable the pathogen colonize the berries. In response to egression, ripe berries reprogrammed different defense responses, though ineffectively