Cyclic nucleotide binding proteins in the Arabidopsis thaliana and Oryza sativa genomes

Our analysis found that several ion channels and a class of thioesterases constitute the possible cyclic nucleotide binding proteins in plants. Contrary to some reports, we found no biochemical or bioinformatic evidence for a plant cyclic nucleotide regulated protein kinase, suggesting that cyclic nucleotide functions in plants have evolved differently than in mammals.This paper provides a molecular framework for the discussion of cyclic nucleotide function in plants, and resolves a longstanding debate about the presence of a cyclic nucleotide dependent kinase in plants.The discovery of cyclic 3'5'-adenosine monophosphate (cAMP) by Earl Sutherland in the late 1950s was one of the most significant paradigm shifts in biochemistry [1]. This breakthrough ushered in the concept of second messengers: intracellular molecules which transmit signals in cells and are derived from an extracellular signal. In the past half century, cyclic nucleotides (both cAMP and cGMP) have been implicated in a vast array of biological phenomena in all kingdoms of life [2].The ubiquitous presence of cyclic nucleotides may be due to several characteristics which make it an ideal second messenger. Cyclic nucleotides are derived in a energetically favourable reaction from common metabolites (ATP and GTP), and can be broken down into non-toxic products (inorganic phosphate and AMP/GMP). The synthesis and degradation of cyclic nucleotides are controlled by enzymes termed adenylate (or guanylate) cyclases and cyclic nucleotide phosphodiesterases, respectively [3,4].In plants, cyclic nucleotides have endured a checkered research history fraught with complications and setbacks. Despite this, recent work has shown unequivocally that cyclic nucleotides are present in plant cells [5,6], and that they play key roles in the regulation of plant physiology [7-9]. Furthermore, the recent identification and cloning of adenylate and guanylate cyclases in plants [7,10] may eventually give clues as to what signa