Search for the Crucial Extracellular Nucleotide Receptor: Kinase Receptor DORN1’s Role in the eATP and eADP Stomatal Signaling Pathways in Arabidopsis thaliana

Extracellular adenosine triphosphate (eATP) functions as a signaling molecule in plants, regulating processes such as root hair growth, wound response, and stomata behavior. Although the eATP receptors in animals have been studied extensively, the equivalent receptors in plants are just beginning to be investigated. Recently, a transmembrane receptor kinase called “Does Not Respond to Nucleotides” (DORN1) was identified as the first eATP receptor in plants. This study was aimed at testing the hypothesis that the DORN1 receptor is the receptor for the eATP signaling pathway regulating stomatal opening and closing. Previous results in Arabidopsis thaliana wild-type plants indicate a bi-phasic response to applied eATP and eADP, with low concentrations inducing stomatal opening and high concentrations inducing stomatal closing. The effects of applied ATP were tested on leaves of Arabidopsis thaliana wild type (Col-0) and the loss-of-function mutant dorn1-3. In addition, ATPγS, the poorly hydrolyzable version of ATP, was tested on wild type and mutant plants. If the dorn1-3 mutant lacks the wild type’s responses to applied eATP, then DORN1 is the likely receptor for the guard cells’ responses to eATP. Another hypothesis tested in this study is whether extracellular adenosine diphosphate (eADP), the hydrolysis product of eATP, controls stomata behavior via DORN1. If dorn1-3 responds like the wild type to eADP, then DORN1 may not be the receptor for the guard cells’ responses to eADP. Using scanning electron microscopy, differences were documented in dorn1-3 and wild type Arabidopsis thaliana leaf epidermal morphology. Altered guard cell patterning with slight clustering of guard cells was observed in the dorn1-3 mutant leaves. Preliminary results support the hypothesis that DORN1 is part of the eATP–induced changes in stomatal aperture, suggesting that DORN1 is the receptor for the eATP signaling pathway in guard cells. In contrast, the preliminary results support the hypothesis that DORN1 is not involved in the eADP signaling pathway in guard cells.