HPtmediated

HPt-mediated refers to signaling processes that rely on histidine-containing phosphotransfer proteins (HPt) as mobile phosphotransfer intermediates to relay phosphate groups between components of a multi-step phosphorelay. HPt proteins participate in two-component signaling in bacteria and in eukaryotes such as plants and fungi, where they couple sensor kinases to response regulators. In plants, the cytokinin signaling pathway is a paradigmatic HPt-mediated relay: cytokinin-activated histidine kinase receptors autophosphorylate, transfer the phosphate to HPt proteins (AHPs), which then transfer it to nuclear transcription factors (ARRs), modulating gene expression and development. In bacteria and fungi, HPt-like proteins such as Spo0B and Ypd1 mediate phosphotransfers within sporulation- or stress-response pathways.

Mechanism: A typical HPt-mediated relay proceeds through a sequential phosphotransfer: a sensor histidine kinase autophosphorylates on a histidine, transfers the phosphate to the HPt protein, which in turn transfers it to a response regulator or transcription factor. This multi-step relay allows signal amplification, spatial distribution, and integration of multiple signals, and can introduce regulatory points for modulation by other proteins or environmental cues.

Significance: HPt-mediated signaling expands the canonical two-component system into multi-step networks, enabling finer control of development, stress responses, and adaptation. Because HPt proteins are mobile and can shuttle between cytosol and nucleus in plants, they provide a mechanism for rapid transduction of extracellular cues into gene expression changes. The concept is widely used to describe signaling in plants, bacteria, and fungi, reflecting conserved principles of histidine-phosphotransfer-based communication.