Transcriptomic Analysis of Ecodormancy Release in Grapevine

Lateral grapevine (Vitis spp.) buds experience three different stages of dormancy: paradormancy during the growing season, endodormancy during early winter, and ecodormancy during late winter. Exposure to low non-freezing temperatures results in the accumulation of chilling, leading to the transition from endo- to ecodormancy. During the winter, buds can also acclimate to very low temperatures, and the degree of cold acclimation in the spring can be used as a measurement of ecodormancy state. Spring temperatures, or warming events during winter, can result in release from ecodormancy and result in an increase in freeze damage risk. Different species and genotypes of grapevine demonstrate variation in cold tolerance, chilling requirement, and time to bud break. In order to better understand the regulation of cold hardiness and dormancy, we undertook a study of gene expression during ecodormancy release.

We studied the transcriptome of 2 cultivated (V. vinifera ‘Cabernet Sauvignon’ and ‘Riesling’) and 2 wild (V. riparia, V. amurensis) grapevine genotypes. Canes were collected from the field in late winter and were placed under forced deacclimation/growth conditions (22 °C, 16/8h light/dark). Bud tissue was harvested daily to assess loss of cold hardiness (proxy for dormancy state) using differential thermal analysis (DTA) as well as for RNA extraction. RNA-Sequencing was performed using Illumina single-end 100bp reads. The rates of deacclimation were similar for all genotypes, however, time to bud break contrasted, allowing us to differentiate changes in gene expression unique to both processes. Pathway analysis using the Vitisnet database of the genes differentially expressed during ecodormancy release indicated enrichment of genes involved in lipid transfer, membrane transport, reactivation of metabolism. Similarly, genes temporally correlated with the budburst process were enriched in pathways for meristem identity, the Auxin pathway and cell expansion. Rapid downregulation of genes was observed in pathways associated with senescence, dehydration, and regulators of stress processes such as NAC domain proteins. Species specific patterns were also detected, suggesting that while the processes of ecodormancy release and budburst are phenotypically similar between wild and cultivated species, novel function or novel regulation of specific genes plays an important role in differentiating dormancy release within Vitis.