Ferredoxin limits cyclic electron flow around PSI (CEF-PSI) in higher plants--stimulation of CEF-PSI enhances non-photochemical quenching of Chl fluorescence in transplastomic tobacco

We tested the hypothesis that ferredoxin (Fd) limits the activity of cyclic electron flow around PSI (CEF-PSI) in vivo and that the relief of this limitation promotes the non-photochemical quenching (NPQ) of Chl fluorescence. In transplastomic tobacco (Nicotiana tabacum cv Xanthi) expressing Fd from Arabidopsis (Arabidopsis thaliana) in its chloroplasts, the minimum yield (F(o)) of Chl fluorescence was higher than in the wild type. F(o) was suppressed to the wild-type level upon illumination with far-red light, implying that the transfer of electrons by Fd-quinone oxidoreductase (FQR) from the chloroplast stroma to plastoquinone was enhanced in transplastomic plants. The activity of CEF-PSI became higher in transplastomic than in wild-type plants under conditions limiting photosynthetic linear electron flow. Similarly, the NPQ of Chl fluorescence was enhanced in transplastomic plants. On the other hand, pool sizes of the pigments of the xanthophyll cycle and the amounts of PsbS protein were the same in all plants. All these results supported the hypothesis strongly. We conclude that breeding plants with an NPQ of Chl fluorescence increased by an enhancement of CEF-PSI activity might lead to improved tolerance for abiotic stresses, particularly under conditions of low light use efficiency.     

Nitrate reductase is responsible for elicitin-induced nitric oxide production in Nicotiana benthamiana

Recent works have established a key role for nitric oxide (NO) in activating disease resistance in plants. Nitrate reductase (NR) is one of the enzymes that are capable of producing NO in plants. In a previous study, we reported that pathogen signals induce expression of NR genes in potato, suggesting the involvement of NR in NO production induced by pathogen signals. In this study, we cloned NR genes from Nicotiana benthamiana and investigated their involvement in NO production induced by INF1, a major elicitin secreted by Phytophthora infestans. Treatment of protoplasts prepared from N. benthamiana leaves with INF1 elevated NO production to a maximum level 1-3 h after treatment. INF1-induced NO generation was suppressed completely by an NO-specific scavenger, but partially by a nitric oxide synthase inhibitor. To investigate the involvement of NR in INF1-induced NO production, NR genes were silenced by virus-induced gene silencing. The NR-silenced plants showed yellowish leaves which resemble the characteristic of Arabidopsis NR double mutants. Silencing of NR genes significantly decreased both NO(2) (-)-producing activity and INF1-induced NO production, indicating that NR is involved in INF1-induced NO production. In contrast, overexpression of NbNR1 encoding N. benthamiana NR by Agrobacterium-mediated transient expression elevated NO(2) (-)-producing activity nine times over the control; however, INF1-induced NO production in protoplasts overexpressing NbNR1 was comparable with that in control protoplasts. These results suggest that NR is involved in INF1-induced NO production, and post-translational modification of NR or availability of substrate NO(2) (-) may be a rate-limiting step of NO production by NR.     

Identification of novel HrpXo regulons preceded by two cis-acting elements, a plant-inducible promoter box and a -10 box-like sequence, from the genome database of Xanthomonas oryzae pv. oryzae

A regulatory protein HrpXo of Xanthomonas oryzae pv. oryzae, the causal agent of bacterial leaf blight of rice, is known to control the expression of hrp genes that encode components of a type III secretion system and of some effector protein genes. In this study, we screened novel HrpXo regulons from the genome database of X. oryzae pv. oryzae, searching for ORFs preceded by two predicted sequence motifs, a plant-inducible promoter box-like sequence and a -10 box-like sequence. Using a gus reporter system, nine of 15 ORF candidates were expressed HrpXo dependently. We also showed by base-substituted mutagenesis that both motifs are essential for the expression of the genes.     

A novel mouse model for MPO-ANCA-associated glomerulonephritis

We established a novel model mouse for myeloperoxidase anti-neutrophil cytoplasmic antibody (MPO-ANCA)-associated glomerulonephritis with crescentic formation, which was induced by administering bovine serum albumin (BSA). Neutrophil infiltration into the renal glomeruli began at 8 weeks and crescent formation was observed from 10 weeks after the first BSA injection. Platelet and neutrophil counts significantly increased, and proteinuria was observed from 5 weeks. MPO-ANCA increased slightly at 4 and markedly at 9 weeks, and the TNF-alpha level increased at 11 weeks. Glomerular neutrophil infiltration was correlated with MPO-ANCA levels. In addition, proteinuria also significantly correlated with MPO-ANCA levels. Finally, renal crescent formation was associated with an increase of MPO-ANCA levels and neutrophil infiltration into glomeruli. The glomerular immune deposition of IgG and C3 was observed. These findings indicate that BSA induces neutrophil activation of peripheral blood followed by the elevation of MPO-ANCA, resulting in the development of crescentic glomerulonephritis in mice.     

Archaeal Diversity and Distribution along Thermal and Geochemical Gradients in Hydrothermal Sediments at the Yonaguni Knoll IV Hydrothermal Field in the Southern Okinawa Trough

A variety of archaeal lineages have been identified using culture-independent molecular phylogenetic surveys of microbial habitats occurring in deep-sea hydrothermal environments such as chimney structures, sediments, vent emissions, and chemosynthetic macrofauna. With the exception of a few taxa, most of these archaea have not yet been cultivated, and their physiological and metabolic traits remain unclear. In this study, phylogenetic diversity and distribution profiles of the archaeal genes encoding small subunit (SSU) rRNA, methyl coenzyme A (CoA) reductase subunit A, and the ammonia monooxygenase large subunit were characterized in hydrothermally influenced sediments at the Yonaguni Knoll IV hydrothermal field in the Southern Okinawa Trough. Sediment cores were collected at distances of 0.5, 2, or 5 m from a vent emission (90°C). A moderate temperature gradient extends both horizontally and vertically (5 to 69°C), indicating the existence of moderate mixing between the hydrothermal fluid and the ambient sediment pore water. The mixing of reductive hot hydrothermal fluid and cold ambient sediment pore water establishes a wide spectrum of physical and chemical conditions in the microbial habitats that were investigated. Under these different physico-chemical conditions, variability in archaeal phylotype composition was observed. The relationship between the physical and chemical parameters and the archaeal phylotype composition provides important insight into the ecophysiological requirements of uncultivated archaeal lineages in deep-sea hydrothermal vent environments, giving clues for approximating culture conditions to be used in future culturing efforts.Deep-sea hydrothermal activity results in diverse physical and chemical environments for the resident microbial communities. Using cultivation techniques and culture-independent molecular analyses, diverse lineages of archaea and bacteria have so far been observed from chimney structures, retrieved in situ colonization systems settled in or on the hydrothermal conduit, microbial mats, sediments, and chemosynthetic macrofaunal bodies (19, 35, 62). Especially in the domain Archaea, most of lineages derived from hydrothermal environments have not yet been cultivated, and little is known about their physiological and metabolic traits.Environmental conditions of the habitat for a particular uncultivated archaeal lineage permit us to speculate about the physiological and metabolic traits of the archaea. For instance, the acidophilic and thermophilic archaeon “Aciduliprofundum boonei,” representing the previously uncultivated deep-sea hydrothermal vent euryarchaeotic group I (DHVEG I) subgroup 2 (DHVE2), has been isolated from a chimney habitat in the Lau Basin (49). In fact, before the cultivation of A. boonei, the DHVE2 was assumed to consist of thermophilic and acidophilic heterotrophs because their habitats had similar characteristics (13, 48, 60, 68). In order to elucidate the distribution patterns of the functionally unknown microbial components in response to the dynamically varying physico-chemical conditions, hydrothermally influenced sediments are considered better study targets than hot vent chimney structures to determine the eco-physiological roles of uncultivated microbes. This is because, unlike vent chimneys, sedimentary habitats affected by subseafloor hydrothermal fluid are expected to have more moderate physico-chemical gradients from mixing of hydrothermal fluid and ambient seawater due to the relatively lower heat convection and hydrothermal fluid penetration. Several studies have already examined the phylogenetic diversity of archaea and bacteria in hydrothermal sediments from the Guaymas Basin (7, 66), the Rainbow vent field in the Mid-Atlantic Ridge (39), and the Iheya Ridge and the Yonaguni Knoll IV in the Okinawa Trough (14, 57). However, only the relationship between the distribution pattern of microbial components and the physico-chemical conditions of these environments has been addressed.The Yonaguni Knoll IV hydrothermal field located at the southern end of the Okinawa Trough is characterized as having thick sediment, several Cl-enriched black smoker sites, and numerous vapor-enriched clear fluid sites (25, 56). The geochemical characterization of these hydrothermal fluids revealed that hydrothermal fluids undergo phase separation under the seafloor (25, 56). Furthermore, the emission of liquid CO₂ droplets has been reported, and occurrence of subseafloor CO₂ hydrate is assumed to have arisen in response to pore water chemistry in the sediments at liquid CO₂ emission sites (14, 25). According to pore water chemistry, it seems likely that these vapor-enriched hydrothermal fluids permeate the sediments around hydrothermal vent sites, and the subseafloor formation-dissociation processes of gas hydrates produce a variety of hydrothermally affected sedimentary habitats (25).In this study, we focused on the “abyss vent” site, which is characterized by 90°C hydrothermal emissions that discharge directly from the seafloor sediments (56). Sediment cores (>25 cm in length) were taken at horizontal distances of 0.5, 2, and 5 m from the hydrothermal emission while the in situ temperature of sediments was measured simultaneously. Vent fluids and interstitial water chemistry of the sediments were characterized along vertical and horizontal gradients of subseafloor mixing zones. Microbial distributions, particularly of archaea, were ascertained by culture-independent molecular analyses targeting the small subunit (SSU) rRNA gene and, mcrA (gene for methyl coenzyme A [CoA] reductase subunit A) and archaeal amoA (gene for ammonia monooxygenase large subunit). Molecular analyses for the functional genes, mcrA and amoA, are expected to indicate diversity and abundance of methanogens, anaerobic methanotrophs, and archaeal ammonium oxidizers that utilize hydrogen, methane, and ammonium, respectively, in hydrothermal fluids as electron donors. In addition, we inferred the phylogenetic diversity and distribution patterns of the bacterial SSU rRNA genes that provide insight into the potential metabolic characteristics and microbial ecosystems in each habitat.     

The ACF1 complex is required for DNA double-strand break repair in human cells

DNA double-strand breaks (DSBs) are repaired via?nonhomologous end-joining (NHEJ) or homologous?recombination (HR), but cellular repair processes remain elusive. We show here that the ATP-dependent chromatin-remodeling factors, ACF1 and SNF2H, accumulate rapidly at DSBs and are required for DSB repair in human cells. If the expression of ACF1 or SNF2H is suppressed, cells become extremely sensitive to X-rays and chemical treatments producing DSBs, and DSBs remain unrepaired. ACF1 interacts directly with KU70 and is required for the accumulation of KU proteins at DSBs. The KU70/80 complex becomes physically more associated with the chromatin-remodeling factors of the CHRAC complex, which includes ACF1, SNF2H, CHRAC15, and CHRAC17, after treatments producing DSBs. Furthermore, the frequency of NHEJ as well as HR induced by DSBs in chromosomal DNA is significantly decreased in cells depleted of either of these factors. Thus, ACF1 and its complexes play important roles in DSBs repair.     

Structural basis for the recognition of nucleophosmin-anaplastic lymphoma kinase oncoprotein by the phosphotyrosine binding domain of Suc1-associated neurotrophic factor-induced tyrosine-phosphorylated target-2

The nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) fusion oncoprotein, formed by the t(2;5) chromosomal translocation in anaplastic large-cell lymphomas, has constitutive tyrosine kinase activity and interacts with a number of signaling molecules. One of the interacting partners of NPM-ALK is the adaptor protein, Suc1-associated neurotrophic factor-induced tyrosine-phosphorylated target (SNT), and mutations that deprive NPM-ALK of all three of the SNT-binding sites significantly reduced the transforming activity. In this study, the interactions of the three binding sites in NPM-ALK with the phosphotyrosine binding (PTB) domain of SNT-2 were analyzed. First, by isothermal titration calorimetry, we found that the phosphorylation-independent binding site in NPM-ALK interacts with the SNT-2 PTB domain more tightly than the phosphorylation-dependent binding sites. Second, the solution structure of the SNT-2 PTB domain in complex with the nonphosphorylated NPM-ALK peptide was determined by nuclear magnetic resonance spectroscopy. The NPM-ALK peptide interacts with the hydrophobic surface of the PTB domain and intermolecularly extends the PTB β-sheet. This interaction mode is much broader and more extensive than those of the phosphorylation-dependent binding sites. Our results indicate that the higher binding activity of the phosphorylation-independent binding site is caused by additional hydrophobic interactions.