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Adenylate cyclases (ACs) catalyse the formation of the second messenger cyclic adenosine 3′,5′-monophosphate (cAMP) from adenosine 5′-triphosphate (ATP). Although cAMP is increasingly recognised as an important signalling molecule in higher plants, ACs have remained somewhat elusive. Here we used a search motif derived from experimentally tested guanylyl cyclases (GCs), substituted the residues essential for substrate specificity and identified the Arabidopsis thaliana K + -uptake permease 7 (AtKUP7) as one of several candidate ACs. Firstly, we show that a recombinant N-terminal, cytosolic domain of AtKUP7 1-100 is able to complement the AC-deficient mutant cyaA in Escherichia coli and thus restoring the fermentation of lactose, and secondly, we demonstrate with both enzyme immunoassays and mass spectrometry that a recombinant AtKUP7 1-100 generates cAMP in vitro. [ABSTRACT FROM AUTHOR]

Cellular and physiological evidence suggests the presence of a novel class of systemically mobile plant molecules that are recognized by antibodies against vertebrate atrial natriuretic peptides (ANPs). In order to characterize the function of these immunoanalogues we have expressed the full-length recombinant (AtPNP-A[1–126]) and demonstrate that this molecule induces osmoticum-dependent H2O uptake into protoplasts at nanomolar concentrations and thus affects cell volume. A similar response is also seen with a recombinant that does not contain the signal peptide (AtPNP-A[26–126]) as well as a short domain (AtPNP-A[33–66]) that shows homology to the vertebrate peptide. Taken together, these findings suggest that AtPNP-A has an important and systemic role in plant growth and homeostasis. [Copyright &y& Elsevier]

Highlights: [•] We show that H2O2 modulates potassium and calcium net fluxes in Arabidopsis roots. [•] We examine the effect of cyclic mononucleotide pre-treatment on these fluxes. [•] We also investigate the effect of cGMP on the microsomal proteome. [•] cGMP is sufficient to induce complex cellular changes to responses induced by H2O2. [Copyright &y& Elsevier]

Abstract: While there is evidence of nitric oxide (NO)-dependent signalling via the second messenger cyclic guanosine 3′,5′-monophosphate (cGMP) in plants, guanylate cyclases (GCs), enzymes that catalyse the formation of cGMP from guanosine 5′-triphosphate (GTP) have until recently remained elusive and none of the candidates identified to-date are NO-dependent. Using both a GC and heme-binding domain specific (H-NOX) search motif, we have identified an Arabidopsis flavin monooxygenase (At1g62580) and shown electrochemically that it binds NO, has a higher affinity for NO than for O2 and that this molecule can generate cGMP from GTP in vitro in an NO-dependent manner. [Copyright &y& Elsevier]

A guanylyl cyclase has been recently identified in Arabidopsis but, despite the use of pharmacological inhibitors to infer roles of the second messenger 3′,5′-cyclic guanosine monophosphate (cGMP), very few measurements of actual cGMP levels in plants are available. Here, we demonstrate that cGMP levels in Arabidopsis seedlings increase rapidly (⩽5 s) and to different degrees after salt and osmotic stress, and that the increases are prevented by treatment with LY, an inhibitor of soluble guanylyl cyclases. In addition, we provide evidence to suggest that salt stress activates two cGMP signalling pathways – an osmotic, calcium-independent pathway and an ionic, calcium-dependent pathway. [Copyright &y& Elsevier]