Transcriptome analysis of grapevine under drought conditions and description of adaptation strategies

Grapevine is one of the most important fruit crops in the world. However, the effect of climate change on Vitis vinifera L. could dramatically affect the productivity of vineyards, causing serious economic and ecological damage. Some of the most important factors are drought and water availability. Varietal sensitivity to these abiotic stresses is more pronounced in commercial cultivars like ‘Merlot’ than local cultivars like ‘Callet’. In order to better understand the adaptive differences between these two cultivars, we used transcriptomic, metabolic and hormonal analyses, at three different levels of drought stress (mild, high and extreme), using Richter 110 as rootstock. Differential gene expression (DGE) analysis was performed using RNA-seq data for each condition in both roots and leaves. DGE results showed that the response started in roots, with more differential expression at mild drought stress in these two cultivars. However, more differentially-expressed genes (DEGs) were found out in ‘Merlot’ than ‘Callet’, with the most significant response to mild drought in ‘Merlot’. However, in high and extreme drought conditions, DGE analysis in leaves showed an increase of DEGs in the two cultivars, being more pronounced in ‘Callet’ than ‘Merlot’, suggesting a different the strategy of response between them. Hormonal and metabolic results displayed two different pathways in drought responses. While ‘Merlot’ allocated more resources to maintain cellular turgor, increasing sugar and alditol concentration in cells, ‘Callet’ produced more secondary metabolites like mono- or sesqui-terpenes, assisting with sugar transport to the fruit and thus increasing berry quality. Furthermore, a higher photosynthetic activity was found in ‘Callet’ than ‘Merlot’, showing higher water use efficiency.