ARK1 is a vegetatively expressed receptor protein kinase gene isolated from Arabidopsis thaliana based on its sequence similarity to Brassica genes involved in pollen-stigma signaling and the self-incompatibility response. This paper shows that the kinase domain of ARK1 autophosphorylates on serine and threonine residues when expressed as a recombinant fusion protein. ARK1 produces a 2.9 kb transcript encoding a transmembrane receptor protein kinase and a 1.4 kb transcript encoding the receptor domain alone. Constitutive high-level expression of ARK1 transcripts in transgenic Arabidopsis resulted in severe stunting and also disrupted normal cellular expansion and differentiation.