Flowering in higher plants is controlled by both the internal and environmental cues. InArabidopsis, several major genetic loci have been defined as the key switches to control flowering. TheFlowering Locus C (FLC) gene has been shown in the autonomous pathway to inhibit the vegetative-to-reproductive transition.FLC appears to be repressed byFlowering Locus D (FLD), which encodes a component of the histone deacetylase complex. Here we report the identification and characterization of a new mutant allelefld-5. Genetic analysis indicates thatfld-5 (in the Wassilewskija background) is allelic to the previously characterizedfld-3 andfld-4 (in the Colombia-0 background). Genetic and molecular analyses reveal thatfld-5 carries a frame-shift mutation, resulting in a premature termination of theFLD open reading frame. TheFLC expression is remarkably increased infld-5, which presumably attributes to the extremely delayed flowering phenotype of the mutant.