Identification of a novel extracellular adenosine 5'-triphosphate receptor in Arabidopsis thaliana

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] In animals, extracellular adenosine 5'-triphosphate (eATP) is a well-studied signaling molecule that is recognized by plasma membrane-localized, P2-type purinergic receptors. In contrast to animals, much less is known about purinergic signaling in plants. In 2014, our laboratory identified the first plant purinoreceptor, P2K1 (DORN1), which is a member of the L-type lectin receptor-like kinase (LecRLK) family. P2K1 is comprised of an extracellular lectin domain, a transmembrane domain and an intracellular kinase domain. In order to identify other plant purinoreceptors, we tested a number of LecRK genes for their ability to complement the inability of p2k1 mutants to induce an elevation in the intracellular calcium concentration upon ATP addition. One such gene, termed P2K2, was found to partially complement the ATP-induced cytosolic calcium response of the p2k1 mutant. Subsequently, we found that the extracellular lectin domain of P2K2 binds to ATP with high affinity (Kd = 40.2[plus or minus]4.5 nanomolar). Interestingly, p2k1, p2k2, and p2k1p2k2 mutant lines are more susceptible to Pseudomonas syringae compared to wild-type. P2K1 and P2K2 interact other and cross-phosphorylate each other during eATP treatment. These data suggest that P2K2 is the second purinergic receptor found in plants and plays an important role in plant immunity.