early in short days 4, a mutation in Arabidopsis that causes early flowering and reduces the mRNA abundance of the floral repressor FLC.

The plant shoot is derived from the apical meristem, a group of stem cells formed during embryogenesis. Lateral organs form on the shoot of an adult plant from primordia that arise on the flanks of the shoot apical meristem. Environmental stimuli such as light, temperature and nutrient availability often influence the shape and identity of the organs that develop from these primordia. In particular, the transition from forming vegetative lateral organs to producing flowers often occurs in response to environmental cues. This transition requires increased expression in primordia of genes that confer floral identity, such as the Arabidopsis gene LEAFY. We describe a novel mutant, early in short days 4 (esd4), that dramatically accelerates the transition from vegetative growth to flowering in Arabidopsis: The effect of the mutation is strongest under short photoperiods, which delay flowering of Arabidopsis: The mutant has additional phenotypes, including premature termination of the shoot and an alteration of phyllotaxy along the stem, suggesting that ESD4 has a broader role in plant development. Genetic analysis indicates that ESD4 is most closely associated with the autonomous floral promotion pathway, one of the well-characterized pathways proposed to promote flowering of Arabidopsis: Furthermore, mRNA levels of a floral repressor (FLC), which acts within this pathway, are reduced by esd4, and the expression of flowering-time genes repressed by FLC is increased in the presence of the esd4 mutation. Although the reduction in FLC mRNA abundance is likely to contribute to the esd4 phenotype, our data suggest that esd4 also promotes flowering independently of FLC. The role of ESD4 in the regulation of flowering is discussed with reference to current models on the regulation of flowering in Arabidopsis.