Transcriptional activator that acts as floral inducer to promote short-day (SD) flowering pathway. Activates Hd3a and other FT-like genes independently from Hd1. May also activate MADS-box transcription factors involved in flowering regulation. Daily oscillation and diurnal expression in plants grown in short day (SD) but not in long day (LD) conditions. Two-component system major event consists of a His-to-Asp phosphorelay between a sensor histidine kinase (HK) and a response regulator (RR). In plants, the His-to-Asp phosphorelay involves an additional intermediate named Histidine-containing phosphotransfer protein (HPt). This multistep phosphorelay consists of a His-Asp-His-Asp sequential transfer of a phosphate group between first an His and an Asp of the HK protein, followed by the transfer to a conserved His of the HPt protein and finally the transfer to an Asp in the receiver domain of the RR protein.