Transcriptomic analysis of the late stages of grapevine (Vitis vinifera cv. Cabernet Sauvignon) berry ripening reveals significant induction of ethylene signaling and flavor pathways in the skin

Grant R Cramer, Ryan Ghan, Karen A Schlauch, Richard L Tillett, Hildegarde Heymann, Alberto Ferrarini, Massimo Delledonne, Sara Zenoni, Marianna Fasoli, Mario Pezzotti

BackgroundGrapevine berry, a nonclimacteric fruit, goes through three developmental stages, the last one is the ripening stage, when the berry changes color and dramatically increases in sugar. Flavors derived from terpenoid and fatty acid metabolism develop at the very end of this ripening stage. Whole-genome microarray analysis was used to assess the transcriptomic response of pulp and skin of Cabernet Sauvignon berries in the late stages of ripening between 22 and 37 °Brix.ResultsThere were approximately 18,000 transcripts whose abundance changed with °Brix level and tissue type. There were a large number of changes in many gene ontology (GO) categories involving metabolism, signaling and abiotic stress. GO categories reflecting tissue differences were overrepresented in photosynthesis, isoprenoid metabolism and pigment biosynthesis. Detailed analysis of the interaction of the skin and pulp with °Brix levels revealed that there were statistically significantly higher abundances of transcripts changing with °Brix level in the skin that were involved in ethylene signaling, isoprenoid and fatty acid metabolism. Many transcripts were peaking around known optimal fruit stages for flavor production. The transcript abundance of approximately two-thirds of the AP2/ERF superfamily of transcription factors changed during these developmental stages. The transcript abundance of a unique clade of ERF6-type transcription factors had the largest changes in the skin and clustered with other genes involved in ethylene, senescence, and fruit flavor production including ACC oxidase, terpene synthases, and lipoxygenases. The transcript abundance of other important transcription factors (i.e. SPL, RIN, etc.) involved in the regulation of fruit ripening was also higher in the skin.ConclusionsA detailed analysis of the transcriptome dynamics during late stages of ripening of grapevine berries revealed that these berries went through massive transcriptional changes in gene ontology categories involving chemical signaling and metabolism in both the pulp and skin, particularly in the skin. Changes in the transcript abundance of genes involved in the ethylene signaling pathway of this nonclimacteric fruit were statistically significant in the late stages of ripening when the production of transcripts for important flavor and aroma compounds were at their highest. Ethylene transcription factors known to play a role in leaf senescence also appear to play a role in fruit senescence. Ethylene may play a bigger role than previously thought in this non-climacteric fruit.