Our analysis indicates that gene duplication events were not the primary mechanism behind the expansion of OsDDE genes in rice. Promoter cis-element analysis combined with haplotype analysis confirmed that OsDDEs regulate the heading date in rice. Specifically, OsDDE9 is a nuclear-localized protein expressed ubiquitously, which promotes heading date by regulating the expression of Ghd7 and Ehd1 under both short-day and long-day conditions. Single-nucleotide polymorphism (SNP) variations in the OsDDE9 promoter leads to changes in promoter activity, resulting in variations in heading dates. This study provides valuable insights into the molecular function and mechanism of the OsDDE genes.