Transcriptional response to hydrogen perioxide in grapevine berry skin at the beginning of ripening

Fleshy fruit ripening represents the final stage of fruit development, when pulp and skin undergo many metabolic and phenotypic transformations to become attractive for seed dispersing animals. In grapevine, the beginning of ripening can be identified by the softening and coloring of the berries (véraison). The transition from mature green to ripening berries is controlled by many internal signals, such as hormones, transcription factors and metabolites, tuned to external stimuli, mainly light, temperature and water availability. Ripening onset is characterized by the gradual loss of photosynthetic activity and a transient shift to an aerobic fermentative metabolism (grapevine is a non climacteric plant) which are likely to favour an oxidative stress. We reported the transient accumulation of hydrogen peroxide (H2O2) and singlet oxygen (1O2) respectively in the cytosol and plastids of Pinot noir berry skin at the beginning of ripening. In order to ascertain the signaling function of H2O2, we treated pre-veraison berries with 1 mM H2O2 and analyzed the transcriptional response at the genome-wide level by RNA-seq. About 230 genes are modulated in green berries in response to H2O2 treatment: they are mainly involved in responses to stimuli and secondary metabolism and are mainly localized at the cell wall. To gain more insights into the function of these genes, a co-expression analysis has been undertaken, using an in-house built grapevine gene expression compendium, called Vitis Colombos. It considers most of the publicly available microarray and RNA-seq gene expression data of grapevine, and provides tools to analyze gene profiles and finding co-expressed genes. These in silico analyses suggest novel gene functional correlations that require experimental validation. The present study contributes new clues to the understanding of the regulatory role played by H2O2 at the beginning of ripening.