Drought stress negatively affects grapevine growth and development.  Grafting with rootstock is widely used to improve the quality of grape fruits and confer drought stress tolerance, but the underlying genetics and regulatory mechanisms are unclear.  Hence, we investigated the physiologic and transcriptomic profiles in the leaves of grafted SM/1103P (SM shoot/1103P root) and self-rooted SM (‘Shine Muscat’) as well as roots of grafted SM/1103P and self-rooted 1103P under drought stress conditions.  The results indicated that grafted grapevine effectively attenuated drought damage in grape leaves by increasing phytohormone levels and antioxidant enzyme activities, reducing H₂O₂ and MDA contents.  Transcriptomic profiling revealed a total of 11,855 and 11,197 differentially expressed genes (DEGs) were identified in grape leaves and roots respectively.  Weighted correlation network analysis (WGCNA) was performed based on the RNA-seq data, and five modules (greenyellow, black, turquoise, salmon and blue) were significantly correlated to drought stress.  Pathway analysis showed that DEGs were enriched in the plant hormone signal transduction and MAPK signaling pathway.  916 transcription factor genes (TFs) belonging to different gene families were detected that may participate in regulating the drought stress.  Quantitative real-time PCR (qRT-PCR) expression analysis of twelve drought stress responsive DEGs was used to verify the transcriptome data.  Furthermore, overexpression of VvMYBPA1 in Arabidopsis thaliana and grape callus tissues improved drought tolerance.  Our findings provided new insights into to the regulatory mechanism for improving grapevine adaptation to drought.  

Gibberellin 2-oxidases (GA2ox) play an important role in regulating the balance of bioactive gibberellins in plants, while the role in the drought response mechanism of grapes remains unclear. In this study, the subcellular localization analysis revealed that VvGA2ox5 was predominantly expressed in the cytoplasm and nucleus. Transient transformation experiment on ‘Pinot noir’ grape leaves showed that overexpression of VvGA2ox5 reduced relative electrical conductivity (REC) and malondialdehyde (MDA) levels and increased proline content, antioxidant enzyme activity, and expression of drought-responsive genes. In contrast, virus-induced gene silencing (VIGS) silenced strains showed the opposite results. Additionally, the overexpression of VvGA2ox5 in ‘Pinot noir’ grape callus and Arabidopsis thaliana (Arabidopsis) further validated its positive function. In the CRISPR-Cas9 grape callus, the experimental results were in contrast to the overexpression lines. Meanwhile, the yeast two-hybrid (Y2H) assay screened a drought-responsive protein, VvDEH (Dehydration-induced 19 homolog 3). RNA-seq analyses showed that overexpression of VvGA2ox5 significantly participates in the hormone signaling pathway. Accordingly, VvGA2ox5 is a crucial regulation gene in enhancing drought tolerance in grapes and serves as a potential candidate gene for improving drought tolerance in plants. This finding offers significant theoretical support for drought tolerance breeding in grapes.