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

Grape quality and yield are affected by bunch rot disease, caused by the necrotrophic fungus Botrytis cinerea. Primary infection often occurs at blooming, although the fungus remains quiescent until maturity and egresses at ripening, causing bunch rot. The molecular dialogue between B. cinerea and the grapevine inflorescence/berry from bloom until maturity is not completely elucidated, although its understanding is vital to implement proper management. In this study, a molecular characterization of the B. cinerea-flower/berry interaction was achieved using transcriptomic and metabolic analysis of the host and the pathogen. Open flowers from fruiting cuttings of 'Pinot Noir' were infected with green fluorescent protein (GFP)-labelled B. cinerea, and samples were collected at 24 and 96 h post-inoculation (hpi) and at 4 and 12 weeks post-inoculation (wpi). Our results indicated that penetration of the flower epidermis by B. cinerea at 24 hpi induced genes encoding virulence factors, representing the effort of the pathogen to invade the host. On the other hand, grapevine flowers responded rapidly, involving genes associated with the accumulation of pathogenesis-related (PR) proteins, stilbenoids, reactive oxygen species and cell-wall reinforcement. At 96 hpi, the transcriptional reaction appeared largely diminished in both the host and the pathogen. Afterwards, infected berries continued their developmental program without any visible symptoms. The interaction between the fungus and the hard, green berries was transcriptionally active. At 12 wpi, the egressed B. cinerea expressed almost all virulence- and growth-related genes to enable the pathogen to colonize the berries. In response to egression, ripe berries reprogramed different defence responses, though they were ineffective.