Transcriptional differences among ripening berries of different density in Tempranillo and Albariño Spanish wine cultivars

Increased temperature and drought, related to climate change, are hastening grapevine reproductive development and ripening and affecting grape berry composition at harvest time, which alters its quality for winemaking. The final composition of the berry reflects not only the genotype but summarizes its interaction with all the environmental conditions experienced by the berry during its ripening process. However, transcriptional analyses reflect a transcriptome composition also dependent on the genotype, but linked to the specific conditions experienced by the berry at the time of sampling. Given the effects of climate change conditions in reproductive development and ripening, berry sampling becomes a crucial step to avoid misinterpretation of transcriptional analyses results influenced by developmental time shifts. In this report we have used berry stratification in NaCl solutions of different densities to characterize consistent transcriptional changes taking places during berry ripening. We have also tested the possible effect of the NaCl based process on berry gene expression to identify any possible interaction of the sample selection method with the transcriptome. The results showed that berries with increased density grown under the same conditions and harvested at the same time displayed gene expression differences affecting about 800 genes which expression is being turned off or turned on during the ripening process independently of vineyard or year. Most of these transcriptional changes are consistent among different cultivars and indicative of increased ripening states. Minor specific transcriptional variation among different density berries could be considered cultivar specific. In addition we showed that exposure to NaCl during the sampling process did not significantly alter berry transcriptome.