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.