Given that a large proportion of the bacteria colonizing the roots of plants is capable of producing N-acyl-L-homoserine lactone (AHL) molecules, it appears likely that these bacterial pheromones may serve as signals for communication between cells of different species. In this study, we have developed and characterized novel Gfp-based monitor strains that allow in situ visualization of AHL-mediated communication between individual cells in the plant rhizosphere. For this purpose, three Gfp-based AHL sensor plasmids that respond to different spectra of AHL molecules were transferred into AHL-negative derivatives of Pseudomonas putida IsoF and Serratia liquefaciens MG1, two strains that are capable of colonizing tomato roots. These AHL monitor strains were used to visualize communication between defined bacterial populations in the rhizosphere of axenically grown tomato plants. Furthermore, we integrated into the chromosome of AHL-negative P. putida strain F117 an AHL sensor cassette that responds to the presence of long-chain AHLs with the expression of Gfp. This monitor strain was used to demonstrate that the indigenous bacterial community colonizing the roots of tomato plants growing in nonsterile soil produces AHL molecules. The results strongly support the view that AHL signal molecules serve as a universal language for communication between the different bacterial populations of the rhizosphere consortium.

Signalling by cGMP-dependent protein kinase type I (cGKI) relaxes various smooth muscles modulating thereby vascular tone and gastrointestinal motility. cGKIdependent relaxation is possibly mediated by phosphorylation of the inositol 1,4,5-trisphosphate receptor I (IP 3 RI)-associated protein (IRAG), which decreases hormone-induced IP 3 -dependent Ca 2 þ release. We show now that the targeted deletion of exon 12 of IRAG coding for the N-terminus of the coiled-coil domain disrupted in vivo the IRAG-IP 3 RI interaction and resulted in hypomorphic IRAG D12/D12 mice. These mice had a dilated gastrointestinal tract and a disturbed gastrointestinal motility. Carbachol-and phenylephrine-contracted smooth muscle strips from colon and aorta, respectively, of IRAG D12/D12 mice were not relaxed by cGMP, while cAMP-mediated relaxation was unperturbed. Norepinephrine-induced increases in [Ca 2 þ ] i were not decreased by cGMP in aortic smooth muscle cells from IRAG D12/D12 mice. In contrast, cGMP-induced relaxation of potassium-induced smooth muscle contraction was not abolished in IRAG D12/D12 mice. We conclude that cGMP-dependent relaxation of hormone receptor-triggered smooth muscle contraction essentially depends on the interaction of cGKI-IRAG with IP 3 RI.

These findings indicate that signalling of cGKIbeta via IRAG is an essential functional part for regulation of smooth muscle tone and of intracellular calcium by NO (exogenously applicated or endogenously synthesized) and by ANP. IRAG signalling does not modulate basal tone but might be important for blood pressure regulation under pathophysiological conditions.

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Introduction Besides the bioavailability of nitric oxide (NO), downstream guanine monophosphate (cGMP) effector proteins are also considered to play a significant role in penile vascular disease. In animal studies, a downregulation of the cGMP-dependent protein kinase-1 (cGKI) α isoform has been linked to erectile dysfunction and diabetes mellitus. So far, the expression of cGKI α and β isoforms has not been evaluated in human penile erectile tissue. Aim To evaluate the expression of cGKI α and β isoforms in relation to smooth muscle α-actin, cGMP, and endothelial NO synthase (eNOS) in human cavernous arteries (HCAs) and human corpus cavernosum (HCC). Methods Cryostat sections of HCA and HCC were incubated with primary antibodies directed against α-actin, cGMP, eNOS, cGKI, cGKI α, and cGKI β. Visualization of double-labeled immunofluorescent stainings was achieved by laser microscopy. Western blot analysis was performed in order to confirm the expression of cGKI isoforms. Main Outcome Measures Expression of cGKI α and β isoforms in relation to smooth muscle α-actin, cGMP, and eNOS in human penile erectile tissue. Results Immunoreactivities specific for cGKI, cGKI α, and cGKI β were observed within the smooth musculature and the endothelium of cavernous arteries and sinusoids. Double stainings revealed the colocalization of alpha-actin, cGMP, eNOS, and cGKI isoforms. The expression of cGKI isoforms was confirmed by Western blot analysis. Conclusions Our results demonstrate, for the first time, the expression of both cGKI α and β isoforms in the smooth musculature of HCA and HCC. Corresponding to recent findings from animal studies, the presence of cGKI α and β provides further evidence for a significant role of these enzymes in the control of smooth muscle function in human penile erectile tissue.