Daily oscillatory transcriptional programs in Grape vine ripening berries

Trabajo presentado en la 2nd Annual ConferenceFleshy Fruit Development & Ripening (COST Action FA1106 QualityFruit), celebrada en Chania (Grecia) del 22 al 25 de septiembre de 2013.Temperature and solar radiation are factors influencing grapevine berry ripening. High temperatures decrease anthocyanin accumulation and hasten organic acid metabolization, while light promotes proanthocynidin and terpenes accumulation. Temperature and radiation conditions cyclically fluctuate in a daily period under field environment. Indeed, the strength of this daily variation affects berry ripening and quality. The intensity of daily temperatures fluctuation modifies flavonoid partitioning, while cold and light during night time enhance anthocyanin accumulation. Transcriptome alterations in grapes under different set temperature and light conditions has been documented. Additionally, a circadian clock signaling that modulate the expression of a high proportion of the genome is present in plants. This circadian clock in connection with other factors controls multiple developmental processes like flowering or dormancy. Nevertheless, the effect of these daily cycling elements over the ripening transcriptional program has not been characterized in detail. In order to determine whether different ripening transcriptional programs are activated during a day in different grape tissues, we followed the berry skin and flesh transcriptome in six time points throughout a 24-hours cycle using the NimbleGen Vitis HX12 microarray. Tempranillo berries with the same density (~19º brix) were selected in all time points from plants grown under controlled greenhouse conditions. In that manner, four different profiles of differentially expressed genes (5% FDR in Limma and ¿2-fold change) were identified in both tissues. Two different oscillatory cycles correlated with them, one involving temperature variation along the 24-hours cycle, while the other presented two opposite peaks at the end of the light and the dark period, respectively. Functional enrichment analysis showed that a thermotolerance response including the activation of HSP chaperones took place at noon time in both tissues. More genes with expression changes following light oscillation were identified in the skin. They were enriched in regulatory genes involved in circadian clock and ethylene signaling pathways as well as in WRKY and AP2 transcription factors and protein kinases. Analogous thermotolerance and signaling responses were found in Verdejo whole pericarp from field grown conditions, while other specific changes could be related with the experimental settings. Genes involved in metabolism were not greatly altered, suggesting that daily variations of conditions could affect berry ripening by mechanisms other than transcriptional control. These results indicate daily oscillatory changes in the grapevine berry transcriptome to occur and they could help to a better understanding of the progress of berry ripening in short term time scales.Peer Reviewe