Identification of an extracellular adenosine 5'-triphosphate receptor in Arabidopsis thaliana
[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI-COLUMBIA AT AUTHOR'S REQUEST.] Adenosine 5'-triphosphate (ATP) is a well-known energy currency in all organisms. However, ATP also acts as a signaling molecule when it is secreted outside the cell. The long-term goal of my research is to understand the molecular mechanism of extracellular ATP recognition and signaling in plants. A signaling role for ATP has been extensively documented in mammalian systems, including human, since the first extracellular ATP receptor was cloned in 1993. Recently, it was shown that extracellular ATP also plays important roles in plant growth, development and stress responses. However, the mechanism of extracellular ATP recognition in plants remains enigmatic. In this dissertation study, we describe a mutant screen that identified a key molecular component involved in extracellular ATP recognition in Arabidopsis thaliana. The gene identified by isolation of an ATP-insensitive mutant was termed dorn1 (Does not Respond to Nucleotides 1), encoding a lectin receptor kinase (At5g60300). The extracellular domain of DORN1 was shown to bind ATP with high affinity (Kd: 45.7 ± 3.1 nM). Mutants defective in DORN1 do not show an ATP-induced calcium response, MAPK activation, or altered gene expression. Wounding of the plant can release up to 40 æM ATP in the wound site. Consistent with this, ectopic expression of DORN1 increased the plant response to physical wounding. We propose that DORN1 is essential for perception of extracellular ATP and likely plays a variety of roles in plant stress responses. Further investigation of DORN1 will greatly enhance our understanding of the extracellular ATP signaling pathway in plants.
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