Regulates flowering time via a photoperiod-dependent pathway. Suppressor of flowering that upregulates HD1 and down-regulates EHD1 in long days (LD), thus leading to the down-regulation of HD3A and RFT1. Triggers OSK4-mediated HD1 phosphorylation. Interacts with OSK3 and OSK4. Mostly expressed in leaves, seedlings and floral organs, and, to a lower extent, in panicle, roots, nodes, internodes, leaf joint and sheath. Follows a diurnal expression pattern; levels increase after dusk, reach a peak before dawn, and damp rapidly thereafter. Slightly shorter plant. Early flowering phenotype in long days (LD) but not in short days (SD).