<p> Heterotrimeric G protein-mediated signalling via activated 7-transmembrane (7TM) serpentine receptors is well known in a range of organisms, but evidence for the existence of this pathway in plants has been elusive. Over the years, however, evidence that G proteins are involved in signal transduction in plants has been accumulating, leading several researchers to seek plant 7TM receptors. </p> <p> The first tangible evidence for a plant 7TM receptor came through an analysis of the expresssed sequence tag database, dbEST. This revealed an Arabidopsis thaliana gene (GCR1) that encodes a protein with 7 predicted TM domains, and other features characteristic of known 7TM receptors [<cite idref="PUB00053651"/>, <cite idref="PUB00053652"/>]. The amino acid sequence of GCR1, however, is unusual in that it shows similarity to receptors from three different 7TM families [<cite idref="PUB00053651"/>, <cite idref="PUB00053652"/>], sharing greatest levels of similarity with the Dictyostelium cAMP receptors. </p> <p> It has been suggested that the cAMP receptors coordinate aggregation of individual cells into a multicellular organism, and regulate the expression of a large number of developmentally-regulated genes [<cite idref="PUB00005114"/>, <cite idref="PUB00001912"/>, <cite idref="PUB00001913"/>]. </p> <p> GCR1 is expressed at low levels in the roots, stems and leaves of Arabidopsis. Studies using transgenic Arabidopsis have suggested a functional role for GCR1 in cytokinin signal transduction [<cite idref="PUB00053652"/>]. </p> GCR1-cAMP receptor