The high-tillering dwarf mutant f2-132 was obtained from the Japonica rice variety F2-285A radiated by 60Co γ- ray. Genetic analysis indicated that this trait was controlled by one single recessive gene, which was mapped between two InDel markers C4-Z3 and C4-Z4 on the long arm of chromosome 4. The physical distance between the two markers is 46kb, which contains a reported high-tillering dwarf gene D17/HTD1. Sequence analysis of the D17 allele in f2-132 showed that the base T at the 395th position in the coding region was substituted by C, which changed the 132th amino acid from phenylalanine to serine. D17/HTD1encodes the carotenoid cleavage dioxygenase 7 (CCD7), which is one of the key enzymes in the biosynthesis pathway of a new plant hormone, strigolactones (SLs). After treatment with GR24, a synthetic analogues of SLs, the tillering phenotype was suppressed.