title: The Arabidopsis thaliana brassinosteroid receptor (AtBRI1) contains a domain that functions as a guanylyl cyclase in vitro.
abstract: BACKGROUND
  Guanylyl cyclases (GCs) catalyze the formation of the second messenger guanosine 3',5'-cyclic monophosphate (cGMP) from guanosine 5'-triphosphate (GTP). Cyclic GMP has been implicated in an increasing number of plant processes, including responses to abiotic stresses such as dehydration and salt, as well as hormones.
  
  
  RESULTS
  Here we used a rational search strategy based on conserved and functionally assigned residues in the catalytic centre of annotated GCs to identify candidate GCs in Arabidopsis thaliana and show that one of the candidates is the brassinosteroid receptor AtBR1, a leucine rich repeat receptor like kinase. We have cloned and expressed a 114 amino acid recombinant protein (AtBR1-GC) that harbours the putative catalytic domain, and demonstrate that this molecule can convert GTP to cGMP in vitro.
  
  
  CONCLUSIONS
  Our results suggest that AtBR1 may belong to a novel class of GCs that contains both a cytosolic kinase and GC domain, and thus have a domain organisation that is not dissimilar to that of atrial natriuretic peptide receptors, NPR1 and NPR2. The findings also suggest that cGMP may have a role as a second messenger in brassinosteroid signalling. In addition, it is conceivable that other proteins containing the extended GC search motif may also have catalytic activity, thus implying that a significant number of GCs, both in plants and animals, remain to be discovered, and this is in keeping with the fact that the single cellular green alga Chlamydomonas reinhardtii contains over 90 annotated putative CGs.
authors.affiliation: Department of Biotechnology, University of the Western Cape, Bellville, South Africa.
authors.forename: Lusisizwe
authors.initials: L
authors.lastname: Kwezi
authors.forename: Stuart
authors.initials: S
authors.lastname: Meier
authors.forename: Lyndon
authors.initials: L
authors.lastname: Mungur
authors.forename: Oziniel
authors.initials: O
authors.lastname: Ruzvidzo
authors.forename: Helen
authors.initials: H
authors.lastname: Irving
authors.forename: Chris
authors.initials: C
authors.lastname: Gehring
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism*; D001483:Base Sequence; D020134:Catalytic Domain; D006152:Cyclic GMP / Q000378:metabolism; D017931:DNA Primers; D006162:Guanylate Cyclase / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011987:Receptors, Steroid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction
chemical_list: D017931:DNA Primers; D011987:Receptors, Steroid; D006162:Guanylate Cyclase; D006152:Cyclic GMP