National Chung Hsing University

About: National Chung Hsing University is a education organization based out in Taichung, Taiwan. It is known for research contribution in the topics: Catalysis & Thin film. The organization has 19443 authors who have published 24060 publications receiving 540154 citations. The organization is also known as: NCHU.

Negative regulation of hrp genes in Pseudomonas syringae by HrpV

Abstract: Mutations in the five hrp and hrc genes in the hrpC operon of the phytopathogen Pseudomonas syringae pv. syringae 61 have different effects on bacterial interactions with host and nonhost plants. The hrcC gene within the hrpC operon encodes an outer membrane component of the Hrp secretion system that is conserved in all type III protein secretion systems and is required for most pathogenic phenotypes and for secretion of the HrpZ harpin to the bacterial milieu. The other four genes (in order), hrpF, hrpG, (hrcC), hrpT, and hrpV, appear to be unique to the group I hrp clusters found in certain phytopathogens (e.g., P. syringae and Erwinia amylovora) and are less well understood. We initiated an examination of their role in Hrp regulation and secretion by determining the effects of functionally nonpolar nptII cartridge insertions in each gene on the production and secretion of HrpZ, as determined by immunoblot analysis of cell fractions. P. syringae pv. syringae 61 hrpF, hrpG, and hrpT mutants were unable to secrete HrpZ, whereas the hrpV mutant overproduced and secreted the protein. This suggested that HrpV is a negative regulator of HrpZ production. Further immunoblot assays showed that the hrpV mutant produced higher levels of proteins encoded by all three of the major hrp operons tested—HrcJ (hrpZ operon), HrcC (hrpC operon), and HrcQB (hrpU operon)—and that constitutive expression of hrpV in trans abolished the production of each of these proteins. To determine the hierarchy of HrpV regulation in the P. syringae pv. syringae 61 positive regulatory cascade, which is composed of HrpRS (proteins homologous with ς54-dependent promoter-enhancer-binding proteins) and HrpL (alternate sigma factor), we tested the ability of constitutively expressed hrpV to repress the activation of HrcJ production that normally accompanies constitutive expression of hrpL or hrpRS. No repression was observed, indicating that HrpV acts upstream of HrpRS in the cascade. The effect of HrpV levels on transcription of the hrpZ operon was determined by monitoring the levels of β-glucuronidase produced by a hrpA′::uidA transcriptional fusion plasmid in different P. syringae pv. syringae 61 strains. The hrpV mutant produced higher levels of β-glucuronidase than the wild type, a hrcU (type III secretion) mutant produced the same level as the wild type, and the strain constitutively expressing hrpV in trans produced low levels equivalent to that of a hrpS mutant. These results suggest that HrpF, HrpG, and HrpT are all components of the type III protein secretion system whereas HrpV is a negative regulator of transcription of the Hrp regulon.

Interaction between Rice MYBGA and the Gibberellin Response Element Controls Tissue-Specific Sugar Sensitivity of α-Amylase Genes

Abstract: Expression of α-amylase genes during cereal grain germination and seedling growth is regulated negatively by sugar in embryos and positively by gibberellin (GA) in endosperm through the sugar response complex (SRC) and the GA response complex (GARC), respectively. We analyzed two α-amylase promoters, αAmy3 containing only SRC and αAmy8 containing overlapped SRC and GARC. αAmy3 was sugar-sensitive but GA-nonresponsive in both rice (Oryza sativa) embryos and endosperms, whereas αAmy8 was sugar-sensitive in embryos and GA-responsive in endosperms. Mutation of the GA response element (GARE) in the αAmy8 promoter impaired its GA response but enhanced sugar sensitivity, and insertion of GARE in the αAmy3 promoter rendered it GA-responsive but sugar-insensitive in endosperms. Expression of the GARE-interacting transcription factor MYBGA was induced by GA in endosperms, correlating with the endosperm-specific αAmy8 GA response. αAmy8 became sugar-sensitive in MYBGA knockout mutant endosperms, suggesting that the MYBGA–GARE interaction overrides the sugar sensitivity of αAmy8. In embryos overexpressing MYBGA, αAmy8 became sugar-insensitive, indicating that MYBGA affects sugar repression. α-Amylase promoters active in endosperms contain GARE, whereas those active in embryos may or may not contain GARE, confirming that the GARE and GA-induced MYBGA interaction prevents sugar feedback repression of endosperm α-amylase genes. We demonstrate that the MYBGA–GARE interaction affects sugar feedback control in balanced energy production during seedling growth and provide insight into the control mechanisms of tissue-specific regulation of α-amylase expression by sugar and GA signaling interference.

Bartonella species and their ectoparasites: Selective host adaptation or strain selection between the vector and the mammalian host?

Abstract: A wide range of blood-sucking arthropods have either been confirmed or are suspected as important vectors in Bartonella transmission to mammals, including humans. Overall, it appears that the diversity of Bartonella species DNA identified in ectoparasites is much broader than the species detected in their mammalian hosts, suggesting a mechanism of adaptation of Bartonella species to their host-vector ecosystem. However, these mechanisms leading to the fitness between the vectors and their hosts still need to be investigated.

Using acetate anions to induce translational isomerization in a neutral urea-based molecular switch

Abstract: Although the use of cations to switch interlocked machine-like systems between different states is quite common, reports of anion-mediated interlocked switches are rare. To the best of our knowledge, only a few examples of anion-controlled translational isomerism in interlocked molecular switches have been described: 1) the generation of a phenoxide anion on a rotaxane thread to attract Leigh$s macrocycle and 2) exchange of the counteranions of ammonium or pyridinium ions to affect their interactions with complementary crown ether or naphthalene-derived recognition motifs. Because of their ability to act as strong Y-shaped hydrogen-bond donors, urea and its derivatives play key roles in the design of receptors for anions, including both spherical halide anions and Y-shaped carboxylate anions, in solution. Conceptually, a [2]pseudorotaxane complex obtained after threading a urea-derived component through the cavity of a macrocycle should be a suitable system for constructing anion-controllable molecular switches because the recognition of anions by the urea recognition site would encourage relocation of the macrocycle to another recognition site. We are unaware, however, of any such switch having been reported to date. Herein, we report a new ditopic macrocyclic host that is capable of recognizing a diphenylurea-derived thread in a [2]pseudorotaxane fashion in solution. The controllable translational isomerism of its corresponding neutral [2]rotaxane was achieved through the addition and removal of acetate anions. Previously, we reported that the diethylene glycol linkages in bis(para-xylyl)-[26]crown-6 (BPX26C6, Scheme 1) located its two xylene rings at a favorable p-stacking distance and, thus, helped its complexation to (mono)pyridinium and 4,4’bipyridinium ions in solution. Because 2,6-pyridinediamide is also an excellent spacer for locating aromatic rings at a suitable p-stacking distance, we designed the ditopic macrocycle 1, which possesses two xylyl rings linked by both diethylene glycol and 2,6-pyridinediamide spacers, as a host molecule capable of complexing diphenylurea derivatives. We expected that the corresponding [2]pseudorotaxane complexes (Scheme 1) would be stabilized through the cooperative effects of p stacking (of the two xylyl rings about the planar p system of the urea center) and N-H···O hydrogen bonding (between the 2,6-pyridinediamide protons and the urea carbonyl oxygen atom and between the urea amide protons and the ethylene glycol oxygen atoms). We obtained macrocycle 1 in 12% overall yield from the reaction of 4-bromomethylbenzonitrile with diethylene glycol under basic conditions (affording the bis(benzonitrile) 2), the LiAlH4-mediated reduction of 2, and subsequent macrocylization with dimethyl 2,6-pyridinedicarboxylate (Scheme 2). To increase the solubility of diphenylurea in less-polar solvents (i.e., solvents that encourage hydrogen bonding between their solutes), we synthesized a diphenylurea derivScheme 1. Formation of a urea-based pseudorotaxane.