Fig. 8

The model of carbon source competition between seed coat and embryo in developing seed of B. napus. During seed development, a part of the carbon source is allocated to the seed coat, and phenylalanine is metabolized into 4-coumarate-CoA to provide one of the substrates (another is malonyl-CoA) for the synthesis of flavonoid compounds and lignin monomers. At the later stage of seed development, oxidized procyanidins and anthocyanins act as important fillers in the endodermis of the seed coat, determining the seed coat color and thickness. Another part of the carbon source is converted to pyruvate by glycolysis to produce acetyl-CoA, which provides the direct substrate malonyl-CoA for the synthesis of FAs and further transformed into stored oil bodies after the synthesis of triacylglycerol. These two processes compete for initial sugar allocation and malonyl-CoA allocation, while the phenylpropane metabolic pathway and FA synthesis pathway, as two important processes determining seed coat development and oil accumulation, are controlled by a strict and complex regulatory mechanism operated by a series of transcription factors