The present invention relates to a technique of increasing the size of plant seeds and the content of storage fat in seeds by using a pyruvic acid transporter in charge of transporting pyruvic acid in a plant and, more specifically, to a composition for increasing the size of plant seeds and the content of storage fat in the seeds, the composition containing the BASS2 protein, which is a pyruvic acid transporter, or a gene encoding the protein, and to a method for increasing the size of plant seeds or the content of storage fat in the seeds, the method comprising a step of introducing the gene and a promoter for overexpressing the gene into a plant. According to the present invention, the fatty acid precursor can be increased by increasing the amount of pyruvic acid transported to the chromatophore at the time of forming seeds, thereby increasing the size of the seeds and the content of storage fat in the seeds, thus expecting the increase of productivity due to the increase in the seed yield. In addition, the content of storage fat in the seeds can be further increased through the increase in the size of the seeds, which corresponds to a main organ for storing plant fat, thereby significantly improving productivity of plant fat (oil) in a restricted space.
