Anthocyanins act as a sugar-buffer and an alternative electron sink in response to starch depletion during leaf senescence: a case study on a typical anthocyanic tree species, Acer japonicum

We hypothesized that anthocyanins act as a sugar-buffer and an alternative electron sink during leaf senescence to prevent sugar-mediated early senescence and photoinhibition. To elucidate the anthocyanin role, we monitored seasonal changes in photosynthetic traits, sugar, starch and N contents, pigment composition, and gene expression profiles in leaves exposed to substantially different light conditions within a canopy of an adult tree of fullmoon maple (Acer japonicum). Enhancement of starch amylolysis accompanied with cessation of starch synthesis occurred in the same manner independent of light conditions. Leaf sugar contents increased, but reached upper limits in the late stage of leaf senescence, even though leaf anthocyanins further increased after complete depletion of starch. Sun-exposed leaves maintained higher energy consumption via electron flow than shade-grown leaves during leaf N resorption. Thus, anthocyanins accumulated in sun-exposed leaves might have a regulative role as a sugar buffer, retarding leaf senescence, and an indirect photoprotective role as an alternative sink for electron consumption to compensate declines in other metabolic processes such as starch and protein synthesis. In this context, anthocyanins might be key substrates protecting both outer-canopy leaves (against photoinhibition) and inner-canopy leaves (via shading by outer-canopy leaves) from high light stress during N resorption.

Reversible down-regulation of photosystems I and II leads to fast photosynthesis recovery after long-term drought in Jatropha curcas

Jatropha curcas is a drought-tolerant plant that maintains its photosynthetic pigments under prolonged drought, and quickly regains its photosynthetic capacity when water is available. It has been reported that drought stress leads to increased thermal dissipation in PSII, but that of PSI has been barely investigated, perhaps due to technical limitations in measuring the PSI absolute quantum yield. In this study, we combined biochemical analysis and spectroscopic measurements using an integrating sphere, and verified that the quantum yields of both photosystems are temporarily down-regulated under drought. We found that the decrease in the quantum yield of PSII was accompanied by a decrease in the core complexes of PSII while light-harvesting complexes are maintained under drought. In addition, in drought-treated plants, we observed a decrease in the absolute quantum yield of PSI as compared with the well-watered control, while the amount of PSI did not change, indicating that non-photochemical quenching occurs in PSI. The down-regulation of both photosystems was quickly lifted in a few days upon re-watering. Our results indicate, that in J. curcas under drought, the down-regulation of both PSII and PSI quantum yield protects the photosynthetic machinery from uncontrolled photodamage.

Exposure to strong irradiance exacerbates photoinhibition and suppresses N resorption during leaf senescence in shade-grown seedlings of fullmoon maple (Acer japonicum)

Leaves of fullmoon maple (Acer japonicum) turn brilliant red with anthocyanins synthesis in autumn. Based on field observations, autumn coloring mainly occurs in outer-canopy leaves exposed to sun, whereas inner-canopy leaves remain green for a certain longer period before finally turn yellowish red with a smaller amount of anthocyanins. Here, we hypothesized that outer-canopy leaves protect themselves against photooxidative stress via anthocyanins while simultaneously shading inner canopy leaves and protecting them from strong light (holocanopy hypothesis). To test this hypothesis, we investigated photoinhibition and leaf N content during autumn senescence in leaves of pot-grown seedlings of fullmoon maple either raised under shade (L0, ≈13% relative irradiance to open) or transferred to full sunlight conditions on 5^th (LH1), 12^th (LH2), or 18^th (LH3) Oct, 2021. Dry mass-based leaf N (N_mass) in green leaves in shade-grown seedlings was ≈ 30 mg N g^-1 in summer. N_mass in shed leaves (25^th Oct to 1^st Nov) was 11.1, 12.0, 14.6, and 10.1 mg N g^-1 in L0, LH1, LH2, and LH3 conditions, respectively. Higher N_mass was observed in shed leaves in LH2, compared to other experimental conditions, suggesting an incomplete N resorption in LH2. F_v/F_m after an overnight dark-adaptation, measured on 19^th Oct when leaf N was actively resorbed, ranked L0: 0.72 > LH3: 0.56 > LH1: 0.45 > LH2: 0.25. As decreased F_v/F_m indicates photoinhibition, leaves in LH2 condition suffered the most severe photoinhibition. Leaf soluble sugar content decreased, but protein carbonylation increased with decreasing F_v/F_m across shade-grown seedlings (L0, LH1, LH2, and LH3) on 19^th Oct, suggesting impaired photosynthetic carbon gain and possible membrane peroxidation induced by photooxidative stress, especially in LH2 condition with less N resorption efficiency. Although the impairment of N resorption seems to depend on the timing and intensity of strong light exposure, air temperature, and consequently the degree of photoinhibition, the photoprotective role of anthocyanins in outer-canopy leaves of fullmoon maple might also contribute to allow a safe N resorption in inner-canopy leaves by prolonged shading.

Characterization of photosystem II assembly complexes containing ONE-HELIX PROTEIN1 in Arabidopsis thaliana

The assembly process of photosystem II (PSII) requires several auxiliary proteins to form assembly intermediates. In plants, early assembly intermediates comprise D1 and D2 subunits of PSII together with a few auxiliary proteins including at least ONE-HELIX PROTEIN1 (OHP1), OHP2, and HIGH-CHLOROPHYLL FLUORESCENCE 244 (HCF244) proteins. Herein, we report the basic characterization of the assembling intermediates, which we purified from Arabidopsis transgenic plants overexpressing a tagged OHP1 protein and named the OHP1 complexes. We analyzed two major forms of OHP1 complexes by mass spectrometry, which revealed that the complexes consist of OHP1, OHP2, and HCF244 in addition to the PSII subunits D1, D2, and cytochrome b₅₅₉. Analysis of chlorophyll fluorescence showed that a major form of the complex binds chlorophyll a and carotenoids and performs quenching with a time constant of 420 ps. To identify the localization of the auxiliary proteins, we solubilized thylakoid membranes using a digitonin derivative, glycodiosgenin, and separated them into three fractions by ultracentrifugation, and detected these proteins in the loose pellet containing the stroma lamellae and the grana margins together with two chlorophyll biosynthesis enzymes. The results indicated that chlorophyll biosynthesis and assembly may take place in the same compartments of thylakoid membranes. Inducible suppression of the OHP2 mRNA substantially decreased the OHP2 protein in mature Arabidopsis leaves without a significant reduction in the maximum quantum yield of PSII under low-light conditions, but it compromised the yields under high-light conditions. This implies that the auxiliary protein is required for acclimation to high-light conditions.

Unique Peripheral Antennas in the Photosystems of the Streptophyte Alga Mesostigma viride

Land plants evolved from a single group of streptophyte algae. One of the key factors needed for adaptation to a land environment is the modification in the peripheral antenna systems of photosystems (PSs). Here, the PSs of Mesostigma viride, one of the earliest-branching streptophyte algae, were analyzed to gain insight into their evolution. Isoform sequencing and phylogenetic analyses of light-harvesting complexes (LHCs) revealed that M. viride possesses three algae-specific LHCs, including algae-type LHCA2, LHCA9 and LHCP, while the streptophyte-specific LHCB6 was not identified. These data suggest that the acquisition of LHCB6 and the loss of algae-type LHCs occurred after the M. viride lineage branched off from other streptophytes. Clear-native (CN)-polyacrylamide gel electrophoresis (PAGE) resolved the photosynthetic complexes, including the PSI-PSII megacomplex, PSII-LHCII, two PSI-LHCI-LHCIIs, PSI-LHCI and the LHCII trimer. Results indicated that the higher-molecular weight PSI-LHCI-LHCII likely had more LHCII than the lower-molecular weight one, a unique feature of M. viride PSs. CN-PAGE coupled with mass spectrometry strongly suggested that the LHCP was bound to PSII-LHCII, while the algae-type LHCA2 and LHCA9 were bound to PSI-LHCI, both of which are different from those in land plants. Results of the present study strongly suggest that M. viride PSs possess unique features that were inherited from a common ancestor of streptophyte and chlorophyte algae.

Substitution of Deoxycholate with the Amphiphilic Polymer Amphipol A8-35 Improves the Stability of Large Protein Complexes during Native Electrophoresis

Native polyacrylamide gel electrophoresis (PAGE) is a powerful technique for protein complex separation that retains both their activity and structure. In photosynthetic research, native-PAGE is particularly useful given that photosynthetic complexes are generally large in size, ranging from 200 kD to 1 MD or more. Recently, it has been reported that the addition of amphipol A8-35 to solubilized protein samples improved protein complex stability. In a previous study, we found that amphipol A8-35 could substitute sodium deoxycholate (DOC), a conventional electrophoretic carrier, in clear-native (CN)-PAGE. In this study, we present the optimization of amphipol-based CN-PAGE. We found that the ratio of amphipol A8-35 to α-dodecyl maltoside, a detergent commonly used to solubilize photosynthetic complexes, was critical for resolving photosynthetic machinery in CN-PAGE. In addition, LHCII dissociation from PSII-LHCII was effectively prevented by amphipol-based CN-PAGE compared with that of DOC-based CN-PAGE. Our data strongly suggest that majority of the PSII-LHCII in vivo forms C2S2M2 at least in Arabidopsis and Physcomitrella. The other forms might appear owing to the dissociation of LHCII from PSII during sample preparation and electrophoresis, which could be prevented by the addition of amphipol A8-35 after solubilization from thylakoid membranes. These results suggest that amphipol-based CN-PAGE may be a better alternative to DOC-based CN-PAGE for the study of labile protein complexes.

Horizontal Transfer of Promiscuous Activity from Nonphotosynthetic Bacteria Contributed to Evolution of Chlorophyll Degradation Pathway

The relationship between enzymes and substrates does not perfectly match the "lock and key" model, because enzymes act on molecules other than their true substrate in different catalytic reactions. Such biologically nonfunctional reactions are called "promiscuous activities." Promiscuous activities are apparently useless, but they can be an important starting point for enzyme evolution. It has been hypothesized that enzymes with low promiscuous activity will show enhanced promiscuous activity under selection pressure and become new specialists through gene duplication. Although this is the prevailing scenario, there are two major problems: 1) it would not apply to prokaryotes because horizontal gene transfer is more significant than gene duplication and 2) there is no direct evidence that promiscuous activity is low without selection pressure. We propose a new scenario including various levels of promiscuous activity throughout a clade and horizontal gene transfer. STAY-GREEN (SGR), a chlorophyll a-Mg dechelating enzyme, has homologous genes in bacteria lacking chlorophyll. We found that some bacterial SGR homologs have much higher Mg-dechelating activities than those of green plant SGRs, while others have no activity, indicating that the level of promiscuous activity varies. A phylogenetic analysis suggests that a bacterial SGR homolog with high dechelating activity was horizontally transferred to a photosynthetic eukaryote. Some SGR homologs acted on various chlorophyll molecules that are not used as substrates by green plant SGRs, indicating that SGR acquired substrate specificity after transfer to eukaryotes. We propose that horizontal transfer of high promiscuous activity is one process of new enzyme acquisition.

Formation of a PSI-PSII megacomplex containing LHCSR and PsbS in the moss Physcomitrella patens

Mosses are one of the earliest land plants that diverged from fresh-water green algae. They are considered to have acquired a higher capacity for thermal energy dissipation to cope with dynamically changing solar irradiance by utilizing both the "algal-type" light-harvesting complex stress-related (LHCSR)-dependent and the "plant-type" PsbS-dependent mechanisms. It is hypothesized that the formation of photosystem (PS) I and II megacomplex is another mechanism to protect photosynthetic machinery from strong irradiance. Herein, we describe the analysis of the PSI-PSII megacomplex from the model moss, Physcomitrella patens, which was resolved using large-pore clear-native polyacrylamide gel electrophoresis (lpCN-PAGE). The similarity in the migration distance of the Physcomitrella PSI-PSII megacomplex to the Arabidopsis megacomplex shown during lpCN-PAGE suggested that the Physcomitrella PSI-PSII and Arabidopsis megacomplexes have similar structures. Time-resolved chlorophyll fluorescence measurements show that excitation energy was rapidly and efficiently transferred from PSII to PSI, providing evidence of an ordered association of the two photosystems. We also found that LHCSR and PsbS co-migrated with the Physcomitrella PSI-PSII megacomplex. The megacomplex showed pH-dependent chlorophyll fluorescence quenching, which may have been induced by LHCSR and/or PsbS proteins with the collaboration of zeaxanthin. We discuss the mechanism that regulates the energy distribution balance between two photosystems in Physcomitrella.

The PSI-PSII Megacomplex in Green Plants

Energy dissipation is crucial for land and shallow-water plants exposed to direct sunlight. Almost all green plants dissipate excess excitation energy to protect the photosystem reaction centers, photosystem II (PSII) and photosystem I (PSI), and continue to grow under strong light. In our previous work, we reported that about half of the photosystem reaction centers form a PSI-PSII megacomplex in Arabidopsis thaliana, and that the excess energy was transferred from PSII to PSI fast. However, the physiological function and structure of the megacomplex remained unclear. Here, we suggest that high-light adaptable sun-plants accumulate the PSI-PSII megacomplex more than shade-plants. In addition, PSI of sun-plants has a deep trap to receive excitation energy, which is low-energy chlorophylls showing fluorescence maxima longer than 730 nm. This deep trap may increase the high-light tolerance of PSI by improving excitation energy dissipation. Electron micrographs suggest that one PSII dimer is directly sandwiched between two PSIs with 2-fold rotational symmetry in the basic form of the PSI-PSII megacomplex in green plants. This structure should enable fast energy transfer from PSII to PSI and allow energy in PSII to be dissipated via the deep trap in PSI.

Evidence of the supercomplex organization of photosystem II and light-harvesting complexes in Nannochloropsis granulata

Diverse light-harvesting complexes (LHCs) have been found in photosynthetic microalgae that originated from secondary endosymbiosis involving primary red algae. However, the associations between LHCs and photosystem I (PSI) and photosystem II (PSII) in these microalgae are not fully understood. Eustigmatophyta is a red algal lineage that appears to have a unique organization in its photosynthetic machinery, consisting of only chlorophyll a and carotenoids that are atypical compared with other closely related groups. In this study, the supramolecular organization of pigment-protein complexes in the eustigmatophyte alga, Nannochloropsis granulata was investigated using Clear Native (CN) PAGE coupled with two-dimensional (2D) SDS-PAGE. Our results showed two slowly migrating green bands that corresponded to PSII supercomplexes, which consisted of reaction centers and LHCs. These green bands were also characterized as PSII complexes by their low temperature fluorescence emission spectra. The protein subunits of the PSII-LHC resolved by 2D CN/SDS-PAGE were analyzed by mass spectrometry, and four different LHC proteins were identified. Phylogenetic analysis of the identified LHC protein sequences revealed that they belonged to four different Lhc groups; (1) stress-related Lhcx proteins, (2) fucoxanthin chlorophyll a/c-binding Lhcf proteins, (3) red-shifted Chromera light-harvesting proteins (Red-CLH), and (4) Lhcr proteins, which are commonly found in organisms possessing red algal plastids. This is the first report showing evidence of a pigment-protein supercomplex consisting of PSII and LHCs, and to identify PSII-associated LHC proteins in Nannochloropsis.

Deficiency of the Stroma-Lamellar Protein LIL8/PSB33 Affects Energy Transfer Around PSI in Arabidopsis

Light-harvesting-like (LIL) proteins are a group of proteins that share a consensus amino acid sequence with light-harvesting Chl-binding (LHC) proteins. We hypothesized that they might be involved in photosynthesis-related processes. In order to gain a better understanding of a potential role in photosynthesis-related processes, we examined the most recently identified LIL protein, LIL8/PSB33. Recently, it was suggested that this protein is an auxiliary PSII core protein which is involved in organization of the PSII supercomplex. However, we found that the majority of LIL8/PSB33 was localized in stroma lamellae, where PSI is predominant. Moreover, the PSI antenna sizes measured under visible light were slightly increased in the lil8 mutants which lack LIL8/PSB33 protein. Analysis of fluorescence decay kinetics and fluorescence decay-associated spectra indicated that energy transfer to quenching sites within PSI was partially hampered in these mutants. On the other hand, analysis of the steady-state fluorescence spectra in these mutants indicates that a population of LHCII is energetically disconnected from PSII. Taken together, we suggest that LIL8/PSB33 is involved in the fine-tuning of light harvesting and/or energy transfer around both photosystems.

PCoM-DB Update: A Protein Co-Migration Database for Photosynthetic Organisms

The identification of protein complexes is important for the understanding of protein structure and function and the regulation of cellular processes. We used blue-native PAGE and tandem mass spectrometry to identify protein complexes systematically, and built a web database, the protein co-migration database (PCoM-DB, http://pcomdb.lowtem.hokudai.ac.jp/proteins/top), to provide prediction tools for protein complexes. PCoM-DB provides migration profiles for any given protein of interest, and allows users to compare them with migration profiles of other proteins, showing the oligomeric states of proteins and thus identifying potential interaction partners. The initial version of PCoM-DB (launched in January 2013) included protein complex data for Synechocystis whole cells and Arabidopsis thaliana thylakoid membranes. Here we report PCoM-DB version 2.0, which includes new data sets and analytical tools. Additional data are included from whole cells of the pelagic marine picocyanobacterium Prochlorococcus marinus, the thermophilic cyanobacterium Thermosynechococcus elongatus, the unicellular green alga Chlamydomonas reinhardtii and the bryophyte Physcomitrella patens. The Arabidopsis protein data now include data for intact mitochondria, intact chloroplasts, chloroplast stroma and chloroplast envelopes. The new tools comprise a multiple-protein search form and a heat map viewer for protein migration profiles. Users can compare migration profiles of a protein of interest among different organelles or compare migration profiles among different proteins within the same sample. For Arabidopsis proteins, users can compare migration profiles of a protein of interest with putative homologous proteins from non-Arabidopsis organisms. The updated PCoM-DB will help researchers find novel protein complexes and estimate their evolutionary changes in the green lineage.

Towards artificial methanogenesis: biosynthesis of the [Fe]-hydrogenase cofactor and characterization of the semi-synthetic hydrogenase

The greenhouse gas and energy carrier methane is produced on Earth mainly by methanogenic archaea. In the hydrogenotrophic methanogenic pathway the reduction of one CO₂ to one methane molecule requires four molecules of H₂ containing eight electrons. Four of the electrons from two H₂ are supplied for reduction of an electron carrier F₄₂₀, which is catalyzed by F₄₂₀-reducing [NiFe]-hydrogenase under nickel-sufficient conditions. The same reaction is catalysed under nickel-limiting conditions by [Fe]-hydrogenase coupled with a reaction catalyzed by F₄₂₀-dependent methylene tetrahydromethanopterin dehydrogenase. [Fe]-hydrogenase contains an iron-guanylylpyridinol (FeGP) cofactor for H₂ activation at the active site. Fe^II of FeGP is coordinated to a pyridinol-nitrogen, an acyl-carbon, two CO and a cysteine-thiolate. We report here on comparative genomic analyses of biosynthetic genes of the FeGP cofactor, which are primarily located in a hmd-co-occurring (hcg) gene cluster. One of the gene products is HcgB which transfers the guanosine monophosphate (GMP) moiety from guanosine triphosphate (GTP) to a pyridinol precursor. Crystal structure analysis of HcgB from Methanococcus maripaludis and its complex with 6-carboxymethyl-3,5-dimethyl-4-hydroxy-2-pyridinol confirmed the physiological guanylyltransferase reaction. Furthermore, we tested the properties of semi-synthetic [Fe]-hydrogenases using the [Fe]-hydrogenase apoenzyme from several methanogenic archaea and a mimic of the FeGP cofactor. On the basis of the enzymatic reactions involved in the methanogenic pathway, we came up with an idea how the methanogenic pathway could be simplified to develop an artificial methanogenesis system.

NDH-Mediated Cyclic Electron Flow Around Photosystem I is Crucial for C4 Photosynthesis

C₄ photosynthesis exhibits efficient CO₂ assimilation in ambient air by concentrating CO₂ around ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) through a metabolic pathway called the C₄ cycle. It has been suggested that cyclic electron flow (CEF) around PSI mediated by chloroplast NADH dehydrogenase-like complex (NDH), an alternative pathway of photosynthetic electron transport (PET), plays a crucial role in C₄ photosynthesis, although the contribution of NDH-mediated CEF is small in C₃ photosynthesis. Here, we generated NDH-suppressed transformants of a C₄ plant, Flaveria bidentis, and showed that the NDH-suppressed plants grow poorly, especially under low-light conditions. CO₂ assimilation rates were consistently decreased in the NDH-suppressed plants under low and medium light intensities. Measurements of non-photochemical quenching (NPQ) of Chl fluorescence, the oxidation state of the reaction center of PSI (P700) and the electrochromic shift (ECS) of pigment absorbance indicated that proton translocation across the thylakoid membrane is impaired in the NDH-suppressed plants. Since proton translocation across the thylakoid membrane induces ATP production, these results suggest that NDH-mediated CEF plays a role in the supply of ATP which is required for C₄ photosynthesis. Such a role is more crucial when the light that is available for photosynthesis is limited and the energy production by PET becomes rate-determining for C₄ photosynthesis. Our results demonstrate that the physiological contribution of NDH-mediated CEF is greater in C₄ photosynthesis than in C₃ photosynthesis, suggesting that the mechanism of PET in C₄ photosynthesis has changed from that in C₃ photosynthesis accompanying the changes in the mechanism of CO₂ assimilation.

Accumulation of the components of cyclic electron flow around photosystem I in C4 plants, with respect to the requirements for ATP

By concentrating CO2, C4 photosynthesis can suppress photorespiration and achieve high photosynthetic efficiency, especially under conditions of high light, high temperature, and drought. To concentrate CO2, extra ATP is required, which would also require a change in photosynthetic electron transport in C4 photosynthesis from that in C3 photosynthesis. Several analyses have shown that the accumulation of the components of cyclic electron flow (CEF) around photosystem I, which generates the proton gradient across thylakoid membranes (ΔpH) and functions in ATP production without producing NADPH, is increased in various NAD-malic enzyme and NADP-malic enzyme C4 plants, suggesting that CEF may be enhanced to satisfy the increased need for ATP in C4 photosynthesis. However, in C4 plants, the accumulation patterns of the components of two partially redundant pathways of CEF, NAD(P)H dehydrogenase-like complex and PROTON GRADIENT REGULATION5-PGR5-like1 complex, are not identical, suggesting that these pathways may play different roles in C4 photosynthesis. Accompanying the increase in the amount of NDH, the expression of some genes which encode proteins involved in the assembly of NDH is also increased at the mRNA level in various C4 plants, suggesting that this increase is needed to increase the accumulation of NDH. To better understand the relation between CEF and C4 photosynthesis, a reverse genetic approach to generate C4 transformants with respect to CEF will be necessary.

Evolution of Green Plants Accompanied Changes in Light-Harvesting Systems

Photosynthetic organisms have various pigments enabling them to adapt to various light environments. Green plants are divided into two groups: streptophytes and chlorophytes. Streptophytes include some freshwater green algae and land plants, while chlorophytes comprise the other freshwater green algae and seawater green algae. The environmental conditions driving the divergence of green plants into these two groups and the changes in photosynthetic properties accompanying their evolution remain unknown. Here, we separated the core antennae of PSI and the peripheral antennae [light-harvesting complexes (LHCs)] in green plants by green-native gel electrophoresis and determined their pigment compositions. Freshwater green algae and land plants have high Chl a/b ratios, with most Chl b existing in LHCs. In contrast, seawater green algae have low Chl a/b ratios. In addition, Chl b exists not only in LHCs but also in PSI core antennae in these organisms, a situation beneficial for survival in deep seawater, where blue-green light is the dominant light source. Finally, low-energy Chl (red Chl) of PSI was detected in freshwater green algae and land plants, but not in seawater green algae. We thus conclude that the different level of Chl b accumulation in core antennae and differences in PSI red Chl between freshwater and seawater green algae are evolutionary adaptations of these algae to their habitats, especially to high- or low-light environments.

Protein co-migration database (PCoM -DB) for Arabidopsis thylakoids and Synechocystis cells

Protein-protein interactions are critical for most cellular processes; however, many remain to be identified. Here, to comprehensively identify protein complexes in photosynthetic organisms, we applied the recently developed approach of blue native PAGE (BN-PAGE) coupled with LC-MS/MS to the thylakoid proteins of Arabidopsis thaliana and the whole cell proteins of whole cell proteins of Synechocystis sp. PCC 6803. We identified 245 proteins from the purified Arabidopsis thylakoid membranes and 1,458 proteins from the whole cells of Synechocystis using the method. Next, we generated protein migration profiles that were assessed by plotting the label-free estimations of protein abundances versus migration distance in BN-PAGE. Comparisons between the migration profiles of the major photosynthetic complexes and their band patterns showed that the protein migration profiles were well correlated. Thus, the protein migration profiles allowed us to estimate the molecular size of each protein complex and to identify co-migrated proteins with the proteins of interest by determining the protein pairs that contained peaks in the same gel slice. Finally, we built the protein co-migration database for photosynthetic organisms (PCoM-DB: http://pcomdb.lowtem.hokudai.ac.jp/proteins/top) to make our data publicly accessible online, which stores the analyzed data with a user-friendly interface to compare the migration profiles of proteins of interest. It helps users to find unidentified protein complexes in Arabidopsis thylakoids and Synechocystis cells. The accumulation of the data from the BN-PAGE coupled with LC-MS/MS should reveal unidentified protein complexes and should aid in understanding the adaptation and the evolution of photosynthetic organisms.

Functional analysis of light-harvesting-like protein 3 (LIL3) and its light-harvesting chlorophyll-binding motif in Arabidopsis

The light-harvesting complex (LHC) constitutes the major light-harvesting antenna of photosynthetic eukaryotes. LHC contains a characteristic sequence motif, termed LHC motif, consisting of 25-30 mostly hydrophobic amino acids. This motif is shared by a number of transmembrane proteins from oxygenic photoautotrophs that are termed light-harvesting-like (LIL) proteins. To gain insights into the functions of LIL proteins and their LHC motifs, we functionally characterized a plant LIL protein, LIL3. This protein has been shown previously to stabilize geranylgeranyl reductase (GGR), a key enzyme in phytol biosynthesis. It is hypothesized that LIL3 functions to anchor GGR to membranes. First, we conjugated the transmembrane domain of LIL3 or that of ascorbate peroxidase to GGR and expressed these chimeric proteins in an Arabidopsis mutant lacking LIL3 protein. As a result, the transgenic plants restored phytol-synthesizing activity. These results indicate that GGR is active as long as it is anchored to membranes, even in the absence of LIL3. Subsequently, we addressed the question why the LHC motif is conserved in the LIL3 sequences. We modified the transmembrane domain of LIL3, which contains the LHC motif, by substituting its conserved amino acids (Glu-171, Asn-174, and Asp-189) with alanine. As a result, the Arabidopsis transgenic plants partly recovered the phytol-biosynthesizing activity. However, in these transgenic plants, the LIL3-GGR complexes were partially dissociated. Collectively, these results indicate that the LHC motif of LIL3 is involved in the complex formation of LIL3 and GGR, which might contribute to the GGR reaction.

Evolutionary changes in chlorophyllide a oxygenase (CAO) structure contribute to the acquisition of a new light-harvesting complex in micromonas

Chlorophyll b is found in photosynthetic prokaryotes and primary and secondary endosymbionts, although their light-harvesting systems are quite different. Chlorophyll b is synthesized from chlorophyll a by chlorophyllide a oxygenase (CAO), which is a Rieske-mononuclear iron oxygenase. Comparison of the amino acid sequences of CAO among photosynthetic organisms elucidated changes in the domain structures of CAO during evolution. However, the evolutionary relationship between the light-harvesting system and the domain structure of CAO remains unclear. To elucidate this relationship, we investigated the CAO structure and the pigment composition of chlorophyll-protein complexes in the prasinophyte Micromonas. The Micromonas CAO is composed of two genes, MpCAO1 and MpCAO2, that possess Rieske and mononuclear iron-binding motifs, respectively. Only when both genes were introduced into the chlorophyll b-less Arabidopsis mutant (ch1-1) was chlorophyll b accumulated, indicating that cooperation between the two subunits is required to synthesize chlorophyll b. Although Micromonas has a characteristic light-harvesting system in which chlorophyll b is incorporated into the core antennas of reaction centers, chlorophyll b was also incorporated into the core antennas of reaction centers of the Arabidopsis transformants that contained the two Micromonas CAO proteins. Based on these results, we discuss the evolutionary relationship between the structures of CAO and light-harvesting systems.

MRP-1/CD9 and KAI1/CD82 expression in normal and various cancer tissues

As part of our evaluation of MRP-1/CD9 and KAI1/CD82 as prognostic predictors among patients with cancer, we have extended our studies to solid tumors of a variety of anatomical sites. Normal tissues were included for comparison. Immunohistochemical techniques were used throughout. Our results indicate that MRP-1/CD9 was strongly expressed by many normal tissues, including the epithelium of the gastrointestinal tract, alveolar epithelium of the lung, urothelium and smooth muscle. Expression was weak in the pituitary gland, spleen and hepatocytes, and absent in testes and spinal cord. KAI1/CD82 was also expressed by many normal tissues, but was absent in some MRP-1/CD9-positive tissues (e.g., smooth muscle, adrenal cortex, urothelium, myelin of peripheral nerves, epithelium of amnion). On the other hand, KAI1/CD82 was strongly expressed in spinal cord gray matter, which was MRP-1/CD9-negative. Expression of these glycoproteins was detected in almost all types of tumors examined. In certain cancers, MRP-1/CD9 and KAI1/CD82 positivity was inversely related to lymph node involvement. Whereas lymph node metastases were present in 22.2% of lung cancer patients whose tumors were MRP-1/CD9 and KAI1/CD82-positive, 65.5% of patients with MRP-1/CD9 and KAI1/CD82-reduced/negative tumors had lymph node metastases. A similar inverse relationship was seen in colon cancer and breast cancer patients with respect to MRP-1/CD9 expression. The present data, together with our previous results suggest that evaluating the MRP1/CD9 and KAI1/CD82 status of cancers of the lung, breast and colon may provide useful information on the metastatic potential of the tumors.

The oligomeric states of the photosystems and the light-harvesting complexes in the Chl b-less mutant

The reversible associations between the light-harvesting complexes (LHCs) and the core complexes of PSI and PSII are essential for the photoacclimation mechanisms in higher plants. Two types of Chls, Chl a and Chl b, both function in light harvesting and are required for the biogenesis of the photosystems. Chl b-less plants have been studied to determine the function of the LHCs because the Chl b deficiency has severe effects specific to the LHCs. Previous studies have shown that the amounts of the LHCs, especially the LHCII trimer, were decreased in the mutants; however, it is still unclear whether Chl b is required for the assembly of the LHCs and for the association of the LHCs with PSI and PSII. Here, to reveal the function of Chl b in the LHCs, we investigated the oligomeric states of the LHCs, PSI and PSII in the Arabidopsis Chl b-less mutant. A two-dimensional blue native-PAGE/SDS-PAGE demonstrated that the PSI-LHCI supercomplex was fully assembled in the absence of Chl b, whereas the trimeric LHCII and PSII-LHCII supercomplexes were not detected. The PSI-NAD(P)H dehydrogenase (NDH) supercomplexes were also assembled in the mutant. Furthermore, we detected two forms of monomeric LHC proteins. The faster migrating forms, which were detected primarily in the mutant, were probably apo-LHC proteins, whereas the slower migrating forms were probably the LHC proteins that contained Chl a. These findings increase our understanding of the Chl b function in the assembly of LHCs and the association of the LHCs with PSI, PSII and NDH.

Allocation of absorbed light energy in PSII to thermal dissipations in the presence or absence of PsbS subunits of rice

The thermal dissipation (TD) of absorbed light energy in PSII is considered to be an important photoprotection process in photosynthesis. A major portion of TD has been visualized through the analysis of Chl fluorescence as energy quenching (qE) which depends on the presence of the PsbS subunit. Although the physiological importance of qE-associated TD (qE-TD) has been widely accepted, it is not yet clear how much of the absorbed light energy is dissipated through a qE-associated mechanism. In this study, the fates of absorbed light energy in PSII with regard to different TD processes, including qE-TD, were quantitatively estimated by the typical energy allocation models using transgenic rice in which psbS genes were silenced by RNA interference (RNAi). The silencing of psbS genes resulted in a decrease in the light-inducible portion of TD, whereas the allocation of energy to electron transport did not change over a wide range of light intensities. The allocation models indicate that the energy allocated to qE-TD under saturating light is 30-50%. We also showed that a large portion of absorbed light energy is thermally dissipated in manners that are independent of qE. The nature of such dissipations is discussed.

Identification of the 7-hydroxymethyl chlorophyll a reductase of the chlorophyll cycle in Arabidopsis

The interconversion of chlorophyll a and chlorophyll b, referred to as the chlorophyll cycle, plays a crucial role in the processes of greening, acclimation to light intensity, and senescence. The chlorophyll cycle consists of three reactions: the conversions of chlorophyll a to chlorophyll b by chlorophyllide a oxygenase, chlorophyll b to 7-hydroxymethyl chlorophyll a by chlorophyll b reductase, and 7-hydroxymethyl chlorophyll a to chlorophyll a by 7-hydroxymethyl chlorophyll a reductase. We identified 7-hydroxymethyl chlorophyll a reductase, which is the last remaining unidentified enzyme of the chlorophyll cycle, from Arabidopsis thaliana by genetic and biochemical methods. Recombinant 7-hydroxymethyl chlorophyll a reductase converted 7-hydroxymethyl chlorophyll a to chlorophyll a using ferredoxin. Both sequence and biochemical analyses showed that 7-hydroxymethyl chlorophyll a reductase contains flavin adenine dinucleotide and an iron-sulfur center. In addition, a phylogenetic analysis elucidated the evolution of 7-hydroxymethyl chlorophyll a reductase from divinyl chlorophyllide vinyl reductase. A mutant lacking 7-hydroxymethyl chlorophyll a reductase was found to accumulate 7-hydroxymethyl chlorophyll a and pheophorbide a. Furthermore, this accumulation of pheophorbide a in the mutant was rescued by the inactivation of the chlorophyll b reductase gene. The downregulation of pheophorbide a oxygenase activity is discussed in relation to 7-hydroxymethyl chlorophyll a accumulation.

Three PsbQ-like proteins are required for the function of the chloroplast NAD(P)H dehydrogenase complex in Arabidopsis

Arabidopsis has three PsbQ-like (PQL) proteins in addition to the PsbQ subunit of the oxygen-evolving complex of PSII. Recent bioinformatic and proteomic studies suggested that the two PQL proteins, PQL1 (At1g14150) and PQL2 (At3g01440), might function in the chloroplast NAD(P)H dehydrogenase (NDH) complex; however, their molecular function has not been characterized. In this study, we examined the function of the chloroplast NDH in the Arabidopsis pql1 and pql2 mutants. Post-illumination increases in Chl fluorescence, which are caused by an NDH-dependent cyclic electron flow, were absent in both mutants, indicating that PQL1 and PQL2 are required for NDH activity. In the thylakoid membranes of wild-type plants, PQL1 and PQL2 were tightly associated with the NDH-PSI supercomplex and protected from protease treatments, while unassembled PQLs were not stably accumulated in mutants lacking known NDH subunits. Subunit stability of the NDH complex was affected differently in the thylakoid membranes of the pql1 and pql2 mutants. These data indicate that PQL1 and PQL2 are novel NDH subunits and differ in their functional roles and in their binding sites in the NDH complex. Furthermore, functional analysis on PQL3 (At2g01918) using the pql3 mutant suggests that PQL3 is also required for NDH activity. Proteins homologous to each PQL protein are found in various plant species, but not in cyanobacteria, algae, mosses or ferns. These results suggest that seed plants that have NDH activity in chloroplasts specifically developed three PQL proteins for the function of the chloroplast NDH complex.

A novel nuclear-encoded protein, NDH-dependent cyclic electron flow 5, is essential for the accumulation of chloroplast NAD(P)H dehydrogenase complexes

The chloroplast NAD(P)H dehydrogenase (NDH) complex, which reduces plastoquinones in thylakoid membranes, is involved in PSI cyclic electron flow and chlororespiration. In addition to land plants, the NDH complex is conserved in cyanobacteria. In this study, we identified a novel NDH-related gene of Arabidopsis, NDH-dependent cyclic electron flow 5 (NDF5, At1g55370). Post-illumination increases in chlorophyll fluorescence were absent in ndf5 mutant plants, which indicated that NDF5 is essential for NDH activity. Sequence analysis did not reveal any known functional motifs in NDF5, but there was some homology in amino acid sequence between NDF5 and NDF2, a known NDH subunit. NDF5 and NDF2 homologs were present in higher plants, but not cyanobacteria. A single homolog, which had similarity to both NDF5 and NDF2, was identified in the moss Physcomitrella patens. Immunoblot analysis showed that NDF5 localizes to membrane fractions of chloroplasts. The stability of NdhH, a subunit of the NDH complex, as well as NDF5 and NDF2, was decreased in ndf5, ndf2 and double ndf2/ndf5 mutants, resulting in a loss of NDH activity in these mutants. These results indicated that both NDF5 and NDF2 have essential functions in the stabilization of the NDH complex. We propose that NDF5 and NDF2 were acquired by land plants during evolution, and that in higher plants both NDF5 and NDF2 are critical to regulate NDH activity and each other's protein stability, as well as the stability of additional NDH subunits.

Three novel subunits of Arabidopsis chloroplastic NAD(P)H dehydrogenase identified by bioinformatic and reverse genetic approaches

Chloroplastic NAD(P)H dehydrogenase (NDH) plays a role in cyclic electron flow around photosystem I to produce ATP, especially in adaptation to environmental changes. Although the NDH complex contains 11 subunits that are homologous to NADH:ubiquinone oxidoreductase (complex I; EC 1.6.5.3), recent genetic and biological studies have indicated that NDH also comprises unique subunits. We describe here an in silico approach based on co-expression analysis and phylogenetic profiling that was used to identify 65 genes as potential candidates for NDH subunits. Characterization of 21 Arabidopsis T-DNA insertion mutants among these ndh gene candidates indicated that three novel ndf (NDH-dependent cyclic electron flow) mutants (ndf1, ndf2 and ndf4) had impaired NDH activity as determined by measurement of chlorophyll fluorescence. The amount of NdhH subunit was greatly decreased in these mutants, suggesting that the loss of NDH activity was caused by a defect in accumulation of the NDH complex. In addition, NDF1, NDF2 and NDF4 proteins co-migrated with the NdhH subunit, as shown by blue native electrophoresis. These results strongly suggest that NDF proteins are novel subunits of the NDH complex. Further analysis revealed that the NDF1 and NDF2 proteins were unstable in the mutants lacking hydrophobic subunits of the NDH complex, but were stable in mutants lacking the hydrophilic subunits, suggesting that NDF1 and NDF2 interact with a hydrophobic sub-complex. NDF4 protein was predicted to possess a redox-active iron-sulfur cluster domain that may be involved in the electron transfer.

NDF6: a thylakoid protein specific to terrestrial plants is essential for activity of chloroplastic NAD(P)H dehydrogenase in Arabidopsis

NAD(P)H dehydrogenase (NDH) is a homolog of respiratory complex I and mediates one of the two pathways of cyclic electron flow around PSI (CEF I). Although 15 ndh subunits have been identified in the chloroplastic and nuclear genomes of higher plants, no electron accepter subunits have been identified to date. To identify the missing chloroplastic NDH subunits, we undertook an in silico approach based on co-expression analysis. In this report, we characterized the novel gene NDF6 (NDH-dependent flow 6; At1g18730) which encodes a protein that is essential for NDH activity. NDF6 has one transmembrane domain and is localized in the thylakoid membrane fraction. Homologous proteins of NDF6 were identified in the genomes of terrestrial plants; however, no homologs have been found in cyanobacteria, which are thought to be the origin of chloroplasts and have a minimal NDH complex unit. NDF6 is unstable in ndhB-impaired or disrupted mutants of higher plants in which the chloroplastic NDH complex is thought to be degraded. These results suggest that NDF6 is a novel subunit of chloroplastic NDH that was added to terrestrial plants during evolution.

Distinct functions for the two PsbP-like proteins PPL1 and PPL2 in the chloroplast thylakoid lumen of Arabidopsis

PsbP, an extrinsic subunit of photosystem II (PSII), is a nuclear-encoded protein that optimizes the water-splitting reaction in vivo. In addition to PsbP, higher plants have two nuclear-encoded genes for PsbP homologs (PsbP-like proteins [PPLs]) that show significant sequence similarity to a cyanobacterial PsbP homolog (cyanoP); however, the function of PPLs in higher plants has not yet been elucidated. In this study, we characterized Arabidopsis (Arabidopsis thaliana) mutants lacking either of two PPLs, PPL1 and PPL2. Phylogenetic analysis suggests that PPL1 would be an ortholog of cyanoP, and PPL2 and PsbP may have a paralogous relationship with PPL1. Analysis on mRNA expression profiles showed that PPL1 expressed under stress conditions and PPL2 coexpressed with the subunits of chloroplast NAD(P)H dehydrogenase (NDH) complex. Consistent with these suggestions, PSII activity in a ppl1 mutant was more sensitive to high-intensity light than wild type, and the recovery of photoinhibited PSII activity was delayed in ppl1 plants. Therefore, PPL1 is required for efficient repair of photodamaged PSII. Furthermore, the stoichiometric level and activity of the chloroplast NDH complex in thylakoids were severely decreased in a ppl2 mutant, demonstrating that PPL2 is a novel thylakoid lumenal factor required for accumulation of the chloroplast NDH complex. These results suggest that during endosymbiosis and subsequent gene transfer to the host nucleus, cyanoP from ancient cyanobacteria evolved into PPL1, PPL2, and PsbP, and each of them has a distinct role in photosynthetic electron transfer in Arabidopsis.

Chemokine receptor CXCR3 promotes colon cancer metastasis to lymph nodes

Chemokines and their receptors are essential for leukocyte trafficking, and also implicated in cancer metastasis to specific organs. We have recently demonstrated that CXCR3 plays a critical role in metastasis of mouse melanoma cells to lymph nodes. Here, we show that some human colon cancer cell lines express CXCR3 constitutively. We constructed cells that expressed CXCR3 cDNA ('DLD-1-CXCR3'), and compared with nonexpressing controls by rectal transplantation in nude mice. Although both cell lines disseminated to lymph nodes at similar frequencies at 2 weeks, DLD-1-CXCR3 expanded more rapidly than the control in 4 weeks. In 6 weeks, 59% of mice inoculated with DLD1-CXCR3 showed macroscopic metastasis in para-aortic lymph nodes, whereas only 14% of those with the control (P<0.05). In contrast, metastasis to the liver or lung was rare, and unaffected by CXCR3 expression. In clinical colon cancer samples, we found expression of CXCR3 in 34% cases, most of which had lymph node metastasis. Importantly, patients with CXCR3-positive cancer showed significantly poorer prognosis than those without CXCR3, or those expressing CXCR4 or CCR7. These results indicate that activation of CXCR3 with its ligands stimulates colon cancer metastasis preferentially to the draining lymph nodes with poorer prognosis.

Fish otolith asymmetry: Morphometry and modeling

Mathematical modeling suggests that relatively large values of otolith mass asymmetry in fishes can alter acoustic functionality and may be responsible for abnormal fish behavior when subjected to weightlessness during parabolic or space flight [D.V. Lychakov, Y.T. Rebane, Otolith mass asymmetry in 18 species of fish and pigeon, J. Grav. Physiol. 11 (3) (2004) 17-34; D.V. Lychakov, Y.T. Rebane, Fish otolith mass asymmetry: morphometry and influence on acoustic functionality, Hear. Res. 201 (2005) 55-69]. The results of morphometric studies of otolith mass asymmetry suppose that the absolute value and the sign of the otolith mass asymmetry can change many times during the growth of individual fish within the range +/-20% [D.V. Lychakov, Y.T. Rebane, Otolith mass asymmetry in 18 species of fish and pigeon, J. Grav. Physiol. 11 (3) (2004) 17-34; D.V. Lychakov, Y.T. Rebane, Fish otolith mass asymmetry: morphometry and influence on acoustic functionality, Hear. Res. 201 (2005) 55-69]. This implies that the adverse effects of otolith asymmetry on acoustic and vestibular functionality could change during the lifetime of an individual fish. The aims of the present article were to examine the nature of otolith mass asymmetry fluctuation and to quantify otolith mass asymmetry in a large number of teleost fishes to verify our previous measurements. A dimensionless measure of otolith mass asymmetry, chi, was calculated as the difference between the masses of the right and left paired otoliths divided by average otolith mass. Saccular otolith mass asymmetry was studied in 59 Mediterranean teleost species (395 otolith pairs), 14 Black Sea teleost species (42 otolith pairs), red drum (196 otolith pairs) and guppy (30 otolith pairs). Utricular otolith mass asymmetry was studied in carp (103 otolith pairs) and goldfish (45 otolith pairs). In accordance with our previous results the value of chi did not depend on fish size (length or mass), systematic or ecological position of the fish, or otolith growth rate. In the great majority of the fishes studied, the saccular otolith chi was small /chi/ <0.05 (or <5%). Mathematical modeling indicates that values of chi vary among individual fish, but that the value is probably stable during a fish's lifetime.

Chloroplastic NAD(P)H dehydrogenase in tobacco leaves functions in alleviation of oxidative damage caused by temperature stress

In this study, the function of the NAD(P)H dehydrogenase (NDH)-dependent pathway in suppressing the accumulation of reactive oxygen species in chloroplasts was investigated. Hydrogen peroxide accumulated in the leaves of tobacco (Nicotiana tabacum) defective in ndhC-ndhK-ndhJ (DeltandhCKJ) at 42 degrees C and 4 degrees C, and in that of wild-type leaves at 4 degrees C. The maximum quantum efficiency of PSII decreased to a similar extent in both strains at 42 degrees C, while it decreased more evidently in DeltandhCKJ at 4 degrees C. The parameters linked to CO(2) assimilation, such as the photochemical efficiency of PSII, the decrease of nonphotochemical quenching following the initial rise, and the photosynthetic O(2) evolution, were inhibited more significantly in DeltandhCKJ than in wild type at 42 degrees C and were seriously inhibited in both strains at 4 degrees C. While cyclic electron flow around PSI mediated by NDH was remarkably enhanced at 42 degrees C and suppressed at 4 degrees C. The proton gradient across the thylakoid membranes and light-dependent ATP synthesis were higher in wild type than in DeltandhCKJ at either 25 degrees C or 42 degrees C, but were barely formed at 4 degrees C. Based on these results, we suggest that cyclic photophosphorylation via the NDH pathway might play an important role in regulation of CO(2) assimilation under heat-stressed condition but is less important under chilling-stressed condition, thus optimizing the photosynthetic electron transport and reducing the generation of reactive oxygen species.

Differential use of two cyclic electron flows around photosystem I for driving CO2-concentration mechanism in C4 photosynthesis

Whereas linear electron flow (LEF) in photosynthesis produces both ATP and NADPH, the cyclic electron flow (CEF) around photosystem I has been shown to produce only ATP. Two alternative routes have been shown for CEF; NAD(P)H dehydrogenase (NDH)- and ferredoxin:plastoquinone oxidoreductase (FQR)-dependent flows, but their physiological relevance has not been elucidated in detail. Meanwhile, because C(4) photosynthesis requires more ATP than does C(3) photosynthesis to concentrate CO(2), it has not been clear how the extra ATP is produced. In this study, to elucidate whether CEF contributes to the additional ATP needed in C(4) photosynthesis, we estimated the amounts of PGR5, which participates in FQR-dependent flow, and NDH-H, a subunit of NDH, in four C(4) species. Although the expression profiles of PGR5 did not correlate well with the additional ATP requirement, NDH was greatly expressed in mesophyll cells in the NAD-malic enzyme (ME) species, and in bundle-sheath cells in NADP-ME species, where there is a strong need for ATP in the respective cells. Our results indicate that CEF via NDH plays a central role in driving the CO(2)-concentrating mechanism in C(4) photosynthesis.

Functional dissection of two Arabidopsis PsbO proteins

PsbO protein is an extrinsic subunit of photosystem II (PSII) and has been proposed to play a central role in stabilization of the catalytic manganese cluster. Arabidopsis thaliana has two psbO genes that express two PsbO proteins; PsbO1 and PsbO2. We reported previously that a mutant plant that lacked PsbO1 (psbo1) showed considerable growth retardation despite the presence of PsbO2 [Murakami, R., Ifuku, K., Takabayashi, A., Shikanai, T., Endo, T., and Sato, F. (2002) FEBS Lett523, 138-142]. In the present study, we characterized the functional differences between PsbO1 and PsbO2. We found that PsbO1 is the major isoform in the wild-type, and the amount of PsbO2 in psbo1 was significantly less than the total amount of PsbO in the wild-type. The amount of PsbO as well as the efficiency of PSII in psbo1 increased as the plants grew; howeVER, it neVER reached the total PsbO level observed in the wild-type, suggesting that the poor activity of PSII in psbo1 was caused by a shortage of PsbO. In addition, an in vitro reconstitution experiment using recombinant PsbOs and urea-washed PSII particles showed that oxygen evolution was better recoVERed by PsbO1 than by PsbO2. Further analysis using chimeric and mutated PsbOs suggested that the amino acid changes Val186-->Ser, Leu246-->Ile, and Val204-->Ile could explain the functional difference between the two PsbOs. Therefore we concluded that both the lower expression level and the inferior functionality of PsbO2 are responsible for the phenotype observed in psbo1.

Ribosomal RNA processing and an RNase R family member in chloroplasts of Arabidopsis

An Arabidopsis mutant rnr1 , which has a defect in the basic genetic system in chloroplasts, was isolated using the screening of the high chlorophyll fluorescence phenotype. Whereas chlorophyll fluorescence and immunoblot studies showed the mutant had reduced activities of photosystems I and II, molecular characterization of the mutant suggested that a T-DNA insertion impaired the expression of a gene encoding a RNase R family member with a targeting signal to chloroplasts. Since RNase R family members have a 3'-5' exoribonuclease activity, we examined the RNA profile in chloroplasts. In rnr1 the intercistronic cleavage between 23S and 4.5S rRNA was impaired, and a significant reduction in rRNA in chloroplasts was found, suggesting that RNR1 functions in the maturation of chloroplast rRNA. The present results suggest that defects in the genetic system in chloroplasts cause high chlorophyll fluorescence, pale green leaf, and marked reduction in the growth rate, whereas the levels of some chloroplast RNA were higher in rnr1 than in the wild-type.

Clinical significance of transmembrane 4 superfamily in colon cancer

Cell motility is an important cellular function closely related to the processes of tumour progression and metastasis. Several members of transmembrane 4 superfamily (TM4SF) have been reported to be associated with cell motility and metastatic potential of solid tumour. The aim of this study is to clarify the clinical significance of the member of TM4SF (MRP-1/CD9, KAI1/CD82 and CD151) in human colon cancer. We studied 146 colon cancer patients who underwent curative surgery and studied the expression of MRP-1/CD9, KAI1/CD82 and CD151 using reverse transcriptase - polymerase chain reaction and immunohistochemistry. We found that 64 patients (43.8%) had MRP-1/CD9-positive tumours and that the overall survival rate of patients with MRP-1/CD9-positive tumours was much higher than that of patients with MRP-1/CD9-negative tumours (89.8 vs 50.8%, P<0.001). In contrast, 63 patients (43.2%) had KAI1/CD82-positive tumours and the overall survival rate of patients with KAI1/CD82-positive tumours was also higher than that of patients with KAI1/CD82-negative tumours (84.8 vs 54.9%, P=0.002). On the other hand, positive CD151 expression had a bad effect on the overall survival rate of patients with colon cancer (61.2 vs 74.9%, P=0.022). In a multivariate analysis, MRP-1/CD9 status was a good indicator of the overall survival (P=0.007). We have shown that the reduction of MRP-1/CD9 and KAI1/CD82 expression, and the increasing CD151 expression are indicators for a poor prognosis in patients with colon cancer. This is a first report describing about the relation between CD151 and colon cancer.

Changes of vertical eye movements of goldfish for different otolith stimulation by linear acceleration

Eye movements serves to hold the gaze steady or to shift the gaze to an object of interest. On Earth, signals from otoliths can be interpreted either as linear motion or as tilt with respect to gravity. In microgravity, static tilt will no longer give rise to changes in otolith activity. However, linear acceleration as well as angular acceleration stimulate the otolith organ. Therefore, during adaptation to microgravity, otolith-mediated response such as eye movements alter. In this study, we analyzed the eye movements of goldfish during linear acceleration. The eye movements during rectangular linear acceleration along the different body axis were video-recorded. The vertical eye rotations were analyzed frame by frame. In normal fish, leftward lateral acceleration induced downward eye rotation in the left eye and upward eye rotation in the right eye. Acceleration from caudal to rostral evoked downward eye rotation in both eyes. When the direction of acceleration was shifted 15 degrees left, the responses in the left eye disappeared. These results suggested that otolith organs in each side were stimulated differently.

Post-illumination reduction of the plastoquinone pool in chloroplast transformants in which chloroplastic NAD(P)H dehydrogenase was inactivated

We reported previously that an ndhB gene disruptant, delta ndhB, had the same phenotype as wild-type tobacco plants under normal growth conditions. Two other groups have reported conflicting phenotypes with each other for ndhCKJ operon disruptants. Here, we generated two transformants in which the ndhCKJ operon was disrupted, and found that new transformants had the same phenotype as delta ndhB. After illumination with visible light, all ndh disruptants had higher levels of steady-state fluorescence than wild-type controls when measured under weak light, suggesting that reduction of the plastoquinone pool in ndh disruptants was greater than that in wild-type controls. The weak light itself could not reduce the plastoquinone much, so the reduction in the plastoquinone in the mutant was due to electron donation from stromal reductants generated during illumination with the strong light. These results supported the hypothesis that NAD(P)H dehydrogenase prevents overreduction in chloroplasts and suggested that chlororespiratory oxidase did not function under low light or in the dark.

Characterization of an Arabidopsis thaliana mutant with impaired psbO, one of two genes encoding extrinsic 33-kDa proteins in photosystem II

A 33-kDa protein component of the oxygen-evolving complex in photosystem II is essential for photosynthesis, and it has been believed that mutants with deletion of this 33-kDa protein are not found in higher plants. We report here the first isolation of an Arabidopsis thaliana mutant with a defect in one of the genes for the 33-kDa proteins, psbO, and an intact gene (psbO2). This mutant showed considerable growth retardation, suggesting that there is a functional difference between psbO and psbO2.

Modulation of intracellular glutathione concentration alters dehydropyrimidine dehydrogenase activity in peripheral blood mononuclear cells

Dehydropyrimidine dehydrogenase (DPD) is the initial key enzyme in the regulation of 5-fluorouracil catabolism and thus controls availability of 5-fluorouracil for anabolism. Modulation of DPD activity may increase the antitumor effect and avoid toxic side effects in 5-fluo-rouracil-based chemotherapy. We measured DPD activity in peripheral blood mononuclear cells from cancer patients and simultaneously monitored intracellular glutathione (GSH) and plasma GSH levels. There was a significant linear relationship between DPD activity and intracellular GSH levels in peripheral blood mononuclear cells obtained from cancer patients. Suppression of intracellular GSH level by buthionine sulfoximine decreased DPD activity, while enhancement of intracellular GSH level by 2-mercaptoethanol increased DPD activity. This study indicated that alteration of intracellular GSH concentration may modulate DPD activity.

Relationship between head orientation and torsional eye movements in goldfish during linear acceleration

We analyzed torsional eye movements of normal goldfish during sinusoidal linear acceleration, altering the orientation of the fish on the linear accelerator in the yaw plane over a range of 90 degrees and in the pitch plane up to 30 degrees. We video-recorded changes of torsional eye movements associated with a body rotation in the yaw and pitch plane and analyzed them frame by frame. In normal fish, we observed clear torsional eye movements for stimuli of 0.1 G linear accelerations along the body axis in the horizontal position. Torsion occurred in the opposite direction of resultant force produced by linear acceleration and gravity. Though the amplitude of these compensatory responses increased with increasing magnitude of acceleration up to 0.5 G, the torsion angle did not fully compensate the angle calculated from gravity and linear acceleration. Furthermore, the torsion angle decreased as the longitudinal body axis deviated from the direction of linear acceleration. For the body axis perpendicular to the direction of acceleration, torsional eye movement was still observed. When we tilted the fish in the pitch plane, compensatory eye torsion occurred. The response amplitude to acceleration decreased for both head-up and head-down up to 30 degrees. These results suggested the existence of specific connections between the otolith organ and ocular muscles.

[Total removal of infected pacemaker lead under cardiopulmonary bypass in a case of endocarditis, bacteremia and lung abscess]

A 60-year-old man, who had undergone implantation of a transvenous pacemaker system on the left chest wall for sick sinus syndrome 19 years ago, was admitted because of endocarditis with septicemia and lung abscess 2 months after reimplantation of the generator. His blood culture revealed Staphylococcus aureus. Following debridement of the infected pacemaker pocket and antibiotics therapy, we tried to remove the pacemaker system under cardiopulmonary bypass 1 month after admission. In intraoperative inspection, the electrodes had become firmly encased with fibrous tissue within the tricuspid valve and the right ventricle. After the operation, antibiotic therapy was performed for 4 weeks. His postoperative course was uneventful. Patients with pacemaker infection should undergo aggressive total removal of the pacemaker system, particularly incase with endocarditis and bacteremia.

Compartmentalization of Peyer's patch anlagen before lymphocyte entry

We have shown that Peyer's patch (PP) first develops as a simple and even cell aggregation during embryogenesis. To investigate when and how such a simple cell aggregation forms the complex PP architecture, we analyzed the distribution of cells expressing IL-7R alpha (PP inducer cells), VCAM-1 (mesenchymal cells), CD11c (dendritic cells), and mature lymphocytes by whole-mount immunostaining of 17.5 days post coitus to 2 days postpartum mouse gut. Our results show that compartmentalization of PP anlagen commences at day 18.5 of gestation by clustering and subsequent follicle formation of IL-7R alpha(+), VCAM-1(+), and CD11c(+) cells. This process adds the primitive architecture of PP anlage with several follicles in which IL-7R alpha(+) cells localize in the center, while VCAM-1(+) and CD11c(+) cells localize at the fringe. This follicle formation is accompanied by the establishment of PP-specific vascular network expressing mucosal addressin cellular adhesion molecule-1. Mature B and T lymphocytes entering in the PP anlage are distributed promptly to their own target zones; B cells to the follicle and T cells to nonfollicular zones. Our analysis of scid/scid mouse indicate that the initial processes including formation of PP-specific vascular network occur in the absence of lymphocytes. These observations indicate that the basic architecture of PP is formed by a set of cell lineages assembled during the initial phase of induction of PP anlagen before entry of mature lymphocytes.

Association of IFN-gamma and IFN regulatory factor 1 polymorphisms with childhood atopic asthma

BACKGROUND

IFN-gamma and related molecules play important roles in the differentiation and function of TH2 cells.

OBJECTIVE

We sought to determine whether IFNG and related genes contribute to any susceptibility to atopic asthma, a representative TH2-dominant disorder.

METHODS

We investigated the association of IFNG (CA repeat polymorphism within the first intron), IRF1 (GT repeat polymorphism within the intron 7), IFNGR1 (Val 14 Met), and IFNGR2 (Gln 64 Arg) gene polymorphisms with atopic asthma in the Japanese child population.

RESULTS

A significant association (P =.0018) was observed between IFNG gene polymorphism and atopic asthma. The tendency was more prominent in patients with age of onset of 3 years or younger (P =.0004) or patients with a family history of allergic diseases (P =.0038). Furthermore, there was a significant association between IRF1 gene whole-allele distribution and atopic asthma (P =.044). The tendency was more prominent in patients with onset at 3 years of age or less (P =.0058). On the other hand, IFNGR1 and IFNGR2 gene polymorphisms showed no association with atopic asthma.

CONCLUSION

These results suggested that among IFNG and related genes, IFNG and IRF1 genes confer genetic susceptibility to atopic asthma in Japanese children.

Lack of association between CD28/CTLA-4 gene polymorphisms and atopic asthma in the Japanese population

Atopic asthma occurs in genetically susceptible individuals in the presence of environmental factors. Recently, the costimulation signal from CD80-CD86 to CD28/CTLA-4 has been suggested to play an important role in the development of atopic asthma. In the present study, we analyzed three polymorphic regions within the CTLA-4 gene, an A/G substitution in exon 1 position 49, a C/T base exchange in the promoter position -318 and an (AT)n repeat polymorphism in the 3'-untranslated region of exon 4, and a CD28 gene polymorphism with a T/C substitution in intron 3 position +17 in 120 patients with atopic asthma and 200 normal controls. The polymorphism frequencies of CTLA-4/CD28 genes in patients did not differ from those in normal controls. Thus, the present study was unable to reveal any association between CTLA-4/CD28 gene polymorphisms and atopic asthma in the Japanese population.

The novel monoclonal antibody MH8-4 inhibiting cell motility recognizes integrin alpha 3: inverse of its expression withmetastases in colon cancer

The molecular basis of cell motility is obviously highly complex and is considered to be controlled by a number of molecular systems including cell adhesion molecules, their receptors, cytoskeletal components, a junctional unit connecting cytoskeletal components and membrane receptors, and various peptide growth factors. The possible involvement of proteins at the cell surface in controlling cell motility has been systematically investigated. Previously, we have addressed this question using functional monoclonal antibodies (MAbs), which inhibit cell motility as probes. In order to further identify cell surface molecules involved in metastasis of gastrointestinal tumors, the present study utilized an approach based on the selection of a colon cancer cell line RPMI4788, which showed high motility out of a large number of human gastrointestinal tumor cell lines. MAb MH8-4 was established after immunization of mice with RPMI4788 and selected on the basis of inhibition of RPMI4788 cell migration in a transwell penetration assay. MH8-4 inhibited the phagokinetic tract motility of various cancer cell lines. A cDNA cloning revealed that MH8-4 recognized a specific protein structure, integrin alpha 3. In order to determine whether these experimental results are of relevance with respect to actual human gastrointestinal tumors, we investigated integrin alpha 3 expression in 40 colon cancers with distant metastases. Our immunohistochemical study showed that in almost 27.5% of the cases, the metastatic tumors had lower integrin alpha 3 levels than their corresponding primary tumors. Moreover, there were no primary tumors with lower integrin alpha 3 expression than their corresponding metastatic tumors. Our data suggest that low integrin alpha 3 expression may be associated with the metastatic potential of certain colon cancers.