page_title: Purinergic signalling
section_title: Evolutionary origins
hierarchical_section_title: Purinergic signalling / Background / Evolutionary origins
caption_attribution_description: Digested fly in a Dionaea muscipula's trap
context_page_description: Purinergic signalling is a form of extracellular signalling mediated by purine nucleotides and nucleosides such as adenosine and ATP. It involves the activation of purinergic receptors in the cell and/or in nearby cells, thereby regulating cellular functions.
  The purinergic signalling complex of a cell is sometimes referred to as the “purinome”.
context_section_description: Purinergic receptors, represented by several families, are among the most abundant receptors in living organisms and appeared early in evolution.
  Among invertebrates, the purinergic signalling system has been found in bacteria, amoeba, ciliates, algae, fungi, anemones, ctenophores, platyhelminthes, nematodes, crustacea, molluscs, annelids, echinoderms, and insects. In green plants, extracellular ATP and other nucleotides induce an increase in the cytosolic concentration of calcium ions, in addition to other downstream changes that influence plant growth and modulate responses to stimuli. In 2014, the first purinergic receptor in plants, DORN1, was discovered.
  The primitive P2X receptors of unicellular organisms often share low sequence similarity with those in mammals, yet they still retain micromolar sensitivity to ATP. The evolution of this receptor class is estimated to have occurred over a billion years ago.
caption: Exogenously applied ATP stimulates the closure of the Venus flytrap[2]
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