VvEXO70A1 acts as a positive regulator conferring dual tolerance to drought and cold in Arabidopsis and grape calli

In grape, EXO70 subunits are essential components of the exocyst tethering complex, which is involved in complex assembly, plant growth and stress-related processes. However, the exact function it performs in facilitating tolerance to drought and cold conditions has yet to be clarified. In this study, we functionally characterized a grape EXO70 isoform, VvEXO70A1, which is predominantly localized at the plasma membrane. Evolutionary analysis of the EXO70 gene family across 11 species indicated that grape EXO70 genes share a conserved phylogenetic history with their orthologs from dicotyledons. The expression of VvEXO70A1 was elevated in overexpression (OE) lines Arabidopsis and grape calli exposed to water deficit and low-temperature treatments. Compared with wild type (WT), VvEXO70A1 overexpressing Arabidopsis and grape calli exhibited enhanced tolerance under these abiotic stresses, which was characterized by both lower levels of oxidative stress markers and a more active antioxidant machinery with substantially higher activities of major ROS-scavenging enzymes, including CAT, SOD, and POD. Notably, the transgenic plants were more sensitive to abscisic acid (ABA), displaying stronger ABA-induced stomatal closure. This phenomenon was further enhanced under drought stress, with the expression of the ABA signaling gene ABF4 being significantly upregulated. Cold stress-related genes (CBF1/2/3, ICE1/2, and ICE1a/b/c) were also strongly induced when the OE lines underwent low-temperature treatment. Overall, overexpression of VvEXO70A1 functions as a positive regulator, boosting tolerance to drought and cold conditions which was accompanied by reduced ROS damage and elevated expression levels of key stress-responsive genes associated with drought and cold in both transgenic Arabidopsis and grape calli.