The BnTFL1‐BnJAM3‐BnSWEETs Module Orchestrates Seed Storage Reserve Accumulation in Brassica napus

ABSTRACT Rapeseed ( Brassica napus L.) is a global oilseed crop, crucial for meeting the increasing global demand for both vegetable oil and protein‐rich animal feed. Transcriptional regulation centrally governs carbon allocation for oil and protein biosynthesis in seeds; however, the key regulators that coordinate these pathways to balance oil and protein levels in B. napus seeds remain largely unknown. In this study, we found that BnaC03.TERMINAL FLOWER 1 (BnaC03.TFL1) and BnaC09.TFL1 function additively to promote soluble sugar and oil biosynthesis while repressing protein deposition, with BnaC03.TFL1 playing the predominant role. BnaC03.TFL1 physically interacts with four BnJASMONATE ASSOCIATED MYC2 LIKE 3 (BnJAM3) proteins that also function additively in enhancing soluble sugar and oil biosynthesis and reducing protein production. Furthermore, BnaC03.TFL1 and BnaA01.JAM3 form a complex that facilitates the transport of soluble sugars from the seed coat to the embryo by directly activating the expression of BnSugar Will Eventually be Exported Transporters ( BnSWEETs ). This complex directs carbon flux into fatty acid biosynthesis at the expense of storage protein production, ultimately fine‐tuning seed oil and protein accumulation. Our findings uncover a BnTFL1‐BnJAM3‐BnSWEETs module that transcriptionally reprograms carbon partitioning to fine‐tune oil and protein accumulation in B. napus seeds.