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Flowering time and plant height are important agronomic traits for crop production. In this study, we characterized a semi-dwarf and late flowering (dlf1) mutation of rice that has pleiotropic effects on these traits. The dlf1 mutation was caused by a T-DNA insertion and the cloned Dlf1 gene was found to encode a WRKY transcription factor (OsWRKY11). The dlf1 mutant contains a T-DNA insertion at the promoter region, leading to enhanced accumulation of Dlf1 transcripts, resulting in a semidominant mutation. The dlf1 mutation suppressed the transcription of Ehd2/RID1/OsId1 and its downstream flowering-time genes including Hd1, Ehd1 and Hd3a under both long-day (LD) and short-day (SD) conditions. Knock-down of Dlf1 expression exhibited early flowering at LD condition related to the wild-type plants. Accumulation of Dlf1 mRNA was observed in most tissues, and two splicing forms of Dlf1 cDNAs were obtained (OsWRKY11.1 and OsWRKY11.2). These two proteins showed transactivation activity in yeast cells. Dlf1 protein was found to be localized in the nucleus. Enhanced expression of OsWRKY11.2 or its 5′ truncated gene showed similar phenotypes to the dlf1 mutant, suggesting that it might function as a negative regulator. We conclude that Dlf1 acts as a transactivator to downregulate Ehd2/RID1/OsId1 in the signal transduction pathway of flowering and plays an important role in the regulation of plant height in rice. [ABSTRACT FROM AUTHOR]