It is found that a transformed plant into which a ³-glutamylcysteine synthetase gene has been introduced is increased in at least one of the number of flowers and the number of seeds in comparison with a wild-type plant, and is therefore increased in seed yield. Based on this finding, the present invention elucidates the function of a product of a plant-derived ³-glutamylcysteine synthetase gene and provides a technique for producing a plant having an increased seed yield.
