Early heading date 2 (Ehd2)/Rice Indeterminate 1 (RID1) is a constitutive activator. Ehd2, oppositely promotes FT-like genes through the upregulation of Ehd1 under unfavorable day-length conditions. Ehd2 mRNA in rice tissues accumulated most abundantly in developing leaves, but was present at very low levels around the shoot apex and in roots, patterns that are similar to those of ID1. The orthologous relationship between rice Ehd2 and maize ID1, which show a very high identity (82%) between their zinc finger domains, had been previously inferred by Colasanti et al. (2006) and supported by evidence of synteny conservation (Rice Chromosome 10 Sequencing Consortium, 2003). Ehd2 plays a pivotal role in the promotion of floral transition in rice under both inductive SD conditions and noninductive LD conditions.