Functions as two-component phosphorelay mediators between cytokinin sensor histidine kinases and response regulators (B-type ARRs). Plays an important role in propagating cytokinin signal transduction through the multistep His-to-Asp phosphorelay (By similarity). Functions as positive regulator of the cytokinin signaling pathway. May play a regulatory role in salt and drought tolerance during plant development (PubMed:24578505). Widely expressed. Histidine-containing phosphotransfer domain (HPt) contains an active histidine that mediates the phosphotransfer. 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. Dwarf, narrow leaf, small grain and low fertility phenotypes. Plant silencing simultaneously OHP1 and OHP2 exhibit phenotypes for a deficiency in cytokinin signaling, including dwarfism with reduced internode lengths, enhanced lateral root growth, early leaf senescence, and reduced tiller numbers and fertility.