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Abstract Adenylyl cyclases (ACs) catalyze the formation of the second messenger cAMP from ATP. Here we report the characterization of an Arabidopsis thaliana leucine-rich repeat (LRR) protein (At3g14460 ; AtLRRAC1) as an adenylyl cyclase. Using an AC-specific search motif supported by computational assessments of protein models we identify an AC catalytic center within the N-terminus and demonstrate that AtLRRAC1 can generate cAMP in vitro. Knock-out mutants of AtLRRAC1 have compromised immune responses to the biotrophic fungus Golovinomyces orontii and the hemibiotrophic bacteria Pseudomonas syringae , but not against the necrotrophic fungus Botrytis cinerea. These findings are consistent with a role of cAMP-dependent pathways in the defense against biotrophic and hemibiotrophic plant pathogens. [ABSTRACT FROM AUTHOR]

Abstract: In plants, the cysteine-rich repeat kinases (CRKs) are a sub-family of receptor-like protein kinases that contain the DUF26 motif in their extracellular domains. It has been shown that in Arabidopsis thaliana, CRK20 is transcriptionally induced by pathogens, salicylic acid and ozone (O3). However, its role in responses to biotic and abiotic stress remains to be elucidated. To determine the function of CRK20 in such responses, two CRK20 loss-of-function mutants, crk20-1 and crk20-2, were isolated from public collections of Arabidopsis T-DNA tagged lines and examined for responses to O3 and Pseudomonas syringae pv. tomato (Pst) DC3000. crk20-1 and crk20-2 showed similar O3 sensitivities and no differences in the expression of defense genes when compared with the wild-type. However, pathogen growth was significantly reduced, while there were no differences in the induction of salicylic acid related defense genes or salicylic acid accumulation. Furthermore, correlation analysis of CRK20 gene expression suggests that it has a role in the control of H2O and/or nutrient transport. We therefore propose that CRK20 promotes conditions that are favorable for Pst DC3000 growth in Arabidopsis, possibly through the regulation of apoplastic homeostasis, and consequently, of the environment of this biotrophic pathogen. [Copyright &y& Elsevier]

Abstract: Plant natriuretic peptides (PNPs) belong to a novel class of peptidic signaling molecules that share some structural similarity to the N-terminal domain of expansins and affect physiological processes such as water and ion homeostasis at nano-molar concentrations. Here we show that a recombinant Arabidopsis thaliana PNP (AtPNP-A) rapidly increased the rate of dark respiration in treated leaves after 5min. In addition, we observed increases in lower leaves, and with a lag time of 10min, the effect spread to the upper leaves and subsequently (after 15min) to the opposite leaves. This response signature is indicative of phloem mobility of the signal, a hypothesis that was further strengthened by the fact that cold girdling, which affects phloem but not xylem or apoplastic processes, delayed the long distance AtPNP-A effect. We conclude that locally applied AtPNP-A can induce a phloem-mobile signal that rapidly modifies plant homeostasis in distal parts. [Copyright &y& Elsevier]