Overexpression of SlANT1 Enhances Drought Tolerance in Tomato Through Anthocyanin-Mediated Antioxidant Protection and Metabolic Reprogramming

Drought stress significantly limits crop yield by disturbing plant water status and redox homeostasis, leading to oxidative stress and growth suppression. Anthocyanins, with their strong antioxidant properties, are closely linked to abiotic stress adaptation. The R2R3-MYB transcription factor SlANT1 promotes anthocyanin biosynthesis in tomato, yet its role in drought resistance remains poorly understood. This study explored the function of SlANT1 in tomato under drought conditions. SlANT1 expression was upregulated under both drought and high salinity. The overexpression of SlANT1 resulted in higher anthocyanin accumulation and reduced leaf and stem dimensions. Under drought, SlANT1-overexpression (SlANT1-OE) plants maintained a greater leaf relative water content, showed less negative water potential, wilted less, and recovered faster after rewatering. These plants also accumulated lower levels of reactive oxygen species (ROS) and malondialdehyde (MDA). While antioxidant enzyme activities were generally reduced, anthocyanin-dependent ROS scavenging was significantly enhanced. SlANT1 overexpression also modulated carbohydrate metabolism and aquaporin gene expression, elevating sucrose, fructose, glucose, and soluble protein while decreasing starch, thereby supporting osmotic adjustment. Notably, while stomata remained partially open in SlANT1-OE plants during drought, they exhibited reduced stomatal density, which likely compensated for the wider apertures and helped maintain favorable water status, while still sustaining higher photosynthetic rates and photosystem II integrity. These findings demonstrate that SlANT1 enhances drought tolerance through coordinated mechanisms involving anthocyanin-mediated antioxidant protection, improved water relations, and the reprogramming of carbohydrate and aquaporin pathways. SlANT1 thus represents a promising target for breeding drought-resilient, high-anthocyanin tomato varieties.