CsSUMO2 Enhances Drought Tolerance through Nuclear Interaction with the E2 Enzyme CsSCE1 in Camellia sinensis

SUMOylation is a conserved post-translational modification critical for plant stress responses. In tea plant (Camellia sinensis), we identified six CsSUMO genes and characterized this family through systematic bioinformatics to investigate their drought-responsive functions. Expression profiling revealed tissue-specific and drought-responsive patterns, with CsSUMO2 markedly up-regulated under drought stress. CsSUMO2 was detected in the nucleus and plasma membrane. Yeast heterologous expression assays further revealed that CsSUMO2 significantly enhances osmotic and salt stress tolerance. Furthermore, antisense oligonucleotide-mediated silencing of CsSUMO2 in tea plants resulted in increased drought sensitivity, elevated malondialdehyde accumulation, and enhanced antioxidant enzyme activities under water deficit conditions. Notably, CsSUMO2 was verified to interact with CsSCE1 in the nucleus via protein interaction assays. Collectively, these findings suggest that the CsSUMO2-CsSCE1 interaction modulates downstream SUMOylation to positively regulate drought tolerance in tea plant. This study provides mechanistic insights into post-translational regulation of stress responses and identifies candidate genes for drought-tolerant tea breeding.