The StSDD1 Positively Regulates Drought Tolerance by Altering Stomatal Density in Solanum tuberosum L.

Drought stress severely impairs crop growth and agricultural productivity. Stomata, specialized structures in the leaf epidermis, play a critical role in gas exchange and transpiration. Therefore, reducing stomatal density to minimize water loss is an effective strategy for enhancing crop drought tolerance. The SDD1 gene was characterized as a negative regulator of stomatal density, and its function has been well characterized in model plants. However, its role in potato remains largely unknown. In this study, we identified a potato SDD1-like gene, StSDD1, which is predominantly expressed in young leaves and induced by drought stress and various hormones. Subcellular localization revealed that the StSDD1 fusion protein localizes to the plasma membrane and cytoplasm. Overexpression of StSDD1 decreased stomatal density and improved water use efficiency, leading to enhanced drought tolerance, whereas knockdown transgenic lines exhibited the opposite phenotype. Additionally, altering StSDD1 expression affected the expression of key stomatal development genes and several physiological and photosynthetic drought-related parameters. Taken together, our results suggest that StSDD1 enhances drought tolerance, potentially by reducing stomatal density. These findings indicate a role for StSDD1 in this process and provide a valuable genetic resource for molecular breeding of drought-resistant crops.