It is intended to provide a polynucleotide encoding a gene capable of regulating tillering and leaf morphology in a plant and a method of regulating the phenotype of a plant by using this polynucleotide. The above-described polynucleotide can regulate the number of leaves or roots per individual or leaf morphology (including the length, width and thickness of leaves). In an embodiment, the plant usable in the regulation of tillering and leaf morphology is a monocotyledon. In a preferred embodiment, the monocotyledon is a gramineae plant. In a still preferred embodiment, the graminieae plant is rice.
