TgZFP9–TgSBP3 and TgDOF5.4–TgPDH Regulatory Networks Drive Photosynthate Allocation to Oil in Torreya grandis Kernels

Torreya grandis is a gymnosperm species valued for oil-rich seeds, yet the molecular mechanism regulating photosynthetic carbon partitioning to storage lipids remains largely unexplored in gymnosperms, which is key to improving oil yield and understanding lipid metabolism. We analyzed two cultivars: Xifei (high-oil) and Zhenzhufei (low-oil). 13C tracing showed intensive carbon reallocation to seeds during oil accumulation, with reduced sucrose, starch, glucose, and fructose, indicating coordinated carbohydrate mobilization and oil biosynthesis. Seed-thinning experiments confirmed that enhanced carbohydrate availability promotes oil accumulation. Transcriptome sequencing combined with weighted gene coexpression network analysis identified sucrose-binding protein 3 (TgSBP3) and pyruvate dehydrogenase (TgPDH) as core nodes, validated by transient overexpression and silencing. Dual-luciferase and DNA–protein binding assays revealed that zinc-finger transcription factor (TgZFP9) and DNA-binding with one finger (DOF) transcription factor (TgDOF5.4) activate TgSBP3 and TgPDH, respectively, regulating oil content and unsaturated fatty acids. We propose a TgZFP9-TgSBP3/TgDOF5.4-TgPDH framework for channeling photoassimilates into storage lipids.