Physio-biochemical and molecular analyses decipher distinct dehydration stress responses in contrasting genotypes of foxtail millet (Setaria italica L.)

Drought impairs plant growth and productivity by disrupting key physiological and biochemical processes. Foxtail millet (Setaria italica), a drought-resilient C₄ crop, is well-suited for climate-smart agriculture, yet its stress adaptation mechanisms remain underexplored. This study deciphered dehydration responses in tolerant and sensitive genotypes, focusing on redox regulation, sugar metabolism, energy dynamics, and autophagy. For this, four drought-distinguished millet genotypes (2 tolerant and 2 sensitive) were subjected to dehydration stress (20 % PEG-6000) for different time points (0, 2, 6 and 12 h). Tolerant genotypes exhibited improved antioxidant enzyme activity and GSH:GSSG ratios, resulting in efficient detoxification of reactive oxygen species (ROS) and improved membrane stability. Sensitive genotypes, in contrast, accumulated ROS and showed elevated oxidative damage and electrolyte leakage. Tolerant genotypes also maintained higher trans-zeatin levels and suppressed chlorophyll degradation, thereby preserving photosynthesis and delaying senescence. Sugar metabolism was more efficient in tolerant types, with increased activities of sugar metabolism enzymes, enabling proper carbohydrate partitioning and osmotic adjustment. Contrastingly, sensitive genotypes showed sugar overaccumulation due to impaired mobilization. Also, tolerant genotypes retained higher ATP and pyruvate levels, indicating better energy homeostasis. Additionally, enhanced autophagy, marked by elevated ATG8 protein and ATG transcript levels, supported cellular recycling in tolerant genotypes. In contrast, repressed autophagy was observed despite increased abscisic acid in sensitive genotypes, likely due to sugar-mediated signalling and elevated trehalose-6-phosphate levels. These integrated responses highlight the roles of redox control, metabolic coordination, and autophagy in dehydration tolerance and offer multi-target strategies for breeding climate-resilient Setaria cultivars for drought-prone environments.