Molecular analysis of the early interaction between the grapevine flower and Botrytis cinerea reveals that prompt activation of specific host pathways leads to fungus quiescence

Grapes quality and yield can be impaired by bunch rot, caused by the necrotrophic fungus Botrytis cinerea. Infection often occurs at flowering and the pathogen stays quiescent until fruit maturity. Here, we report a molecular analysis of the early interaction between B. cinerea and Vitis vinifera flowers, using a controlled infection system, confocal microscopy and integrated transcriptomic and metabolic analysis of the host and the pathogen. Flowers from fruiting cuttings of the cv. Pinot Noir were infected with GFP-labeled B. cinerea and studied at 24 and 96 hours post inoculation (hpi). We observed that penetration of the epidermis by B. cinerea coincided with increased expression of genes encoding cell wall-degrading enzymes, phytotoxins, and proteases. Grapevine responded with a rapid defense reaction involving 1193 genes associated with the accumulation of antimicrobial proteins, polyphenols, reactive oxygen species and cell wall reinforcement. At 96 hpi the reaction appears largely diminished both in the host and in the pathogen. Our data indicate that the defense responses of the grapevine flower collectively are able to restrict invasive fungal growth into the underlying tissues, thereby forcing the fungus to enter quiescence until the conditions become more favorable to resume pathogenic development