Physiological and transcriptomic responses of two grapevine rootstock genotypes to drought treatments

Grapevines are relatively tolerant to water deficit, although severe drought can affect grape quality and yield. Plants responses to drought stress vary depending on the severity of stress and the stage of drought progression. The drought tolerance can be associated with water use efficiency, stomatal conductance, plant hydraulic conductance, rooting depth and leaf dehydration tolerance. Nevertheless, the molecular mechanisms underlying the adaptation of grapevine to water shortage remain less investigated. In this study, physiological and transcriptomic responses induced by water stress exposure in leaves and roots of drought tolerant and susceptible rootstocks were compared. The effect of progressive drought treatments was studied under controlled environmental conditions on grafted (with Cabernet Sauvignon) and ungrafted plants of 101.14 and 1103P rootstocks grown in pots. The sampling was performed at 3 different times: T0, plants at 80% soil water content (SWC); T1, plants at 50% SWC; T2, plants at 20% SWC. The control plants were maintained at 80% SWC overall the experiment. Shoot growth, plant water status and leaf photosynthetic parameters were measured at each experimental time. For transcriptomic analysis, fully expanded leaves and whole root systems were collected. Total RNA has been extracted from all samples and tagged mRNA stranded libraries for differential expression analysis have been produced. Each pooled library was sequenced on an Illumina HiSeq 2000 platform with 2 × 50 bps paired-end runs. Base calling and quality control were performed through Illumina RTA sequence analysis pipeline. Illumina reads have been used to determine gene expression. Differential expressed genes (DEG) have been quantified either through the alignment against the Pinot Noir genome and ab-initio transcript reconstruction. Large differences between genotypes, in terms of phenotypic behavior and transcriptome regulation, were observed. DEGs among samples have been correlated to physiological responses