Grapevine RD22a constitutive expression in tobacco enhances stomatal adjustment and confers drought tolerance

Drought is one of the major constraints limiting crop production worldwide including grapevine. Investigations of drought tolerance genotypes by genetic engineering are an important goal in Vitis breeding program. Three dehydration-responsive RD22 genes (VviRD22) were identified in Vitis vinifera L. Here, we aim to evaluate the constitutive expression of VviRD22a effect on tobacco performance under low water availability conditions, namely under drought and under osmotic stress. In vitro, and under osmotic stress, transgenic seeds of tobacco showed an enhanced tolerance at the germination and seedling stages compared to the wild-type (WT). When drought was applied ex vitro by stopping irrigation during 9 days, transgenic lines exhibited an earlier decrease of stomatal conductance that was, interestingly, followed by an internal adjustment leading to a moderate decline of the photosynthetic rate. Additionally, differences between WT and transgenics under both control and stressed conditions were revealed at ultrastructural level through shape alteration within the transgenics. Additionally, the performances of the VviRD22a lines under drought were notably maintained in terms of biomass production (vegetative dry material) and water status (Relative water content and water retention ability). A significant distinctiveness between VviRD22a-expressing lines and WT under stress conditions but not under control conditions (principal component analyses) was found. Protection effect of VviRD22a constitutive expression towards drought involved root biomass, water status and stomatal adjustment traits. Overall, our data suggest that VviRD22a transgenic expression plays a positive role in drought tolerance improvement supporting it as an important candidate gene for molecular breeding of drought tolerant grapevines.