The present invention provides transgenic zoysiagrass plant cells transformed with a modified oat phytochrome A gene (S598A) in which the serine-598 codon was replaced with an alanine codon, which, when expressed, significantly suppresses shade avoidance reactions, such as dwarfish internodes and petioles, short leaves, increased branching, and dark-green leaf color. Said transgenic zoysiagrass shows a robust appearance and is expected to show enhanced resistance to biotic and abiotic stresses. Also provided are a recombinant DNA construct comprising the S598A gene which, when expressed, induces drastic suppression of shade avoidance reactions, transgenic plants produced by this method, and propagating seeds obtained from said transgenic plants.