Plant Photochemistry, Reactive Oxygen Species, and Photoprotection

Light energy, absorbed as photons by chlorophylls and other pigment molecules consisting of light-harvesting complexes (LHCs), is transferred to the reaction centres (RCs), where, through charge separation, electrons flow from photosystem II (PSII) through cytochrome b6f and diffusible electron carriers to photosystem I (PSI) [...]

Transcriptome Profiling of Cu Stressed Petunia Petals Reveals Candidate Genes Involved in Fe and Cu Crosstalk

Copper (Cu) is an essential element for most living plants, but it is toxic for plants when present in excess. To better understand the response mechanism under excess Cu in plants, especially in flowers, transcriptome sequencing on petunia buds and opened flowers under excess Cu was performed. Interestingly, the transcript level of FIT-independent Fe deficiency response genes was significantly affected in Cu stressed petals, probably regulated by basic-helix-loop-helix 121 (bHLH121), while no difference was found in Fe content. Notably, the expression level of bHLH121 was significantly down-regulated in petals under excess Cu. In addition, the expression level of genes related to photosystem II (PSII), photosystem I (PSI), cytochrome b6/f complex, the light-harvesting chlorophyll II complex and electron carriers showed disordered expression profiles in petals under excess Cu, thus photosynthesis parameters, including the maximum PSII efficiency (FV/FM), nonphotochemical quenching (NPQ), quantum yield of the PSII (ΦPS(II)) and photochemical quenching coefficient (qP), were reduced in Cu stressed petals. Moreover, the chlorophyll a content was significantly reduced, while the chlorophyll b content was not affected, probably caused by the increased expression of chlorophyllide a oxygenase (CAO). Together, we provide new insight into excess Cu response and the Cu–Fe crosstalk in flowers.

Electron carriers involved in autotrophic and heterotrophic acetogenesis in the thermophilic bacterium Thermoanaerobacter kivui

Thermoanaerobacter kivui is an acetogenic model organism that reduces CO2 with electrons derived from H2 or CO, or from organic substrates in the Wood–Ljugdahl pathway (WLP). For the calculation of ATP yields, it is necessary to know the electron carriers involved in coupling of the oxidative and reductive parts of metabolism. Analyses of key catabolic oxidoreductases in cell-free extract (CFE) or with purified enzymes revealed the physiological electron carriers involved. The glyceraldehyde-3-phosphate dehydrogenase (GA3P-DH) assayed in CFE was NAD+-specific, NADP+ was used with less than 4% and ferredoxin (Fd) was not used. The methylene-THF dehydrogenase was NADP+-specific, NAD+ or Fd were not used. A Nfn-type transhydrogenase that catalyzes reduced Fd-dependent reduction of NADP+ with NADH as electron donor was also identified in CFE. The electron carriers used by the potential electron-bifurcating hydrogenase (HydABC) could not be unambiguously determined in CFE for technical reasons. Therefore, the enzyme was produced homologously in T. kivui and purified by affinity chromatography. HydABC contained 33.9 ± 4.5 mol Fe/mol of protein and FMN; it reduced NADP+ but not NAD+. The methylene-THF reductase (MetFV) was also produced homologously in T. kivui and purified by affinity chromatography. MetFV contained 7.2 ± 0.4 mol Fe/mol of protein and FMN; the complex did neither use NADPH nor NADH as reductant but only reduced Fd. In sum, these analysis allowed us to propose a scheme for entire electron flow and bioenergetics in T. kivui.

Aspects of the Neurospora crassa Sulfur Starvation Response Are Revealed by Transcriptional Profiling and DNA Affinity Purification Sequencing

Identification of nutrients present in the environment is a challenge common to all organisms. Sulfur is an important nutrient source found in proteins, lipids, and electron carriers that are required for the survival of filamentous fungi such as Neurospora crassa .

First-Principles Study of Carrier-Mediated and Vacancy-Induced Ferromagnetism in Molybdenum Disulfide Monolayer

We have investigated the magnetic properties of semiconducting molybdenum disulfide (MoS2) monolayer (ML) using the plane wave self-consistent field (PWscf) method within the framework of density functional theory (DFT). The pristine semiconducting bulk MoS2 is nonmagnetic (NM), due to the spin pairing of two electrons. We have indicated that the carrier-mediated ferromagnetism is available on the MoS2 ML as both the hole and electron carriers. The ordinary neutral S (VS0) vacancy creates the localized vacancy defect level and this level does not create the ferromagnetic (FM) state due to the spin pairing of two electrons by three Mo dangling bonds. While we have shown that the FM state is possible to create the FM state, due to the additional hole and electron carriers on the valency band and localized vacancy defect level by positively and negatively charged S (VS1+ and VS1- ) and positively charged Mo (VMo1+) vacancies.

First-principles study of the vacancy defects in ZnIn2Te4 and CdIn2Te4

First-principles calculations were carried out to study the stability and electronic properties of native vacancy defects in the semiconducting ZnIn2Te4 (ZIT) and CdIn2Te4 (CIT). The Zn/Cd and In vacancies are acceptor defects, while the Te vacancy is donor defect. However, the In and Te vacancies dominate in the [Formula: see text]-type and [Formula: see text]-type semiconducting environments, respectively. The Te vacancy is not excited, so it could not compensate the majority of free carriers. The In vacancy prefers to be excited, which generates free hole carriers to compensate the majority of electron carriers. The Zn vacancy is rare in a typical semiconducting environment. Furthermore, all the vacancies induce localized defect states which may be trap centers for the free carriers. Accordingly, these native vacancy defects are destructive for the development of solar cells based on ZIT and CIT, so they should be avoided as much as possible during the growth process.

ZmFdC2 Encoding a Ferredoxin Protein With C-Terminus Extension Is Indispensable for Maize Growth

As important electron carriers, ferredoxin (Fd) proteins play important roles in photosynthesis, and the assimilation of CO2, nitrate, sulfate, and other metabolites. In addition to the well-studied Fds, plant genome encodes two Fd-like protein members named FdC1 and FdC2, which have extension regions at the C-terminus of the 2Fe-2S cluster. Mutation or overexpression of FdC genes caused alterations in photosynthetic electron transfer rate in rice and Arabidopsis. Maize genome contains one copy of each FdC gene. However, the functions of these genes have not been reported. In this study, we identified the ZmFdC2 gene by forward genetics approach. Mutation of this gene causes impaired photosynthetic electron transport and collapsed chloroplasts. The mutant plant is seedling-lethal, indicating the indispensable function of ZmFdC2 gene in maize development. The ZmFdC2 gene is specifically expressed in photosynthetic tissues and induced by light treatment, and the encoded protein is localized on chloroplast, implying its specialized function in photosynthesis. Furthermore, ZmFdC2 expression was detected in both mesophyll cells and bundle sheath cells, the two cell types specialized for C4 and C3 photosynthesis pathways in maize. Epigenomic analyses showed that ZmFdC2 locus was enriched for active histone modifications. Our results demonstrate that ZmFdC2 is a key component of the photosynthesis pathway and is crucial for the development of maize.

Co-feeding glucose with either gluconate or galacturonate during clostridial fermentations provides metabolic fine-tuning capabilities

Clostridiumacetobutylicum ATCC 824 effectively utilizes a wide range of substrates to produce commodity chemicals. When grown on substrates of different oxidation states, the organism exhibits different recycling needs of reduced intracellular electron carrying co-factors. Ratios of substrates with different oxidation states were used to modulate the need to balance electron carriers and demonstrate fine-tuned control of metabolic output. Three different oxidized substrates were first fed singularly, then in different ratios to three different strains of Clostridium sp. Growth was most robust when fed glucose in exclusive fermentations. However, the use of the other two more oxidized substrates was strain-dependent in exclusive feeds. In glucose-galacturonate mixed fermentation, the main products (acetate and butyrate) were dependant on the ratios of the substrates. Exclusive fermentation on galacturonate was nearly homoacetic. Co-utilization of galacturonate and glucose was observed from the onset of fermentation in growth conditions using both substrates combined, with the proportion of galacturonate present dictating the amount of acetate produced. For all three strains, increasing galacturonate content (%) in a mixture of galacturonate and glucose from 0 to 50, and 100, resulted in a corresponding increase in the amount of acetate produced. For example, C.acetobutylicum increased from ~ 10 mM to ~ 17 mM, and then ~ 23 mM. No co-utilization was observed when galacturonate was replaced with gluconate in the two substrate co-feed.

A new twist of rubredoxin function in M. tuberculosis

Electron transfer mediated by metalloproteins drives many biological processes. Rubredoxins are ubiquitous iron-containing electron carriers that play important roles in bacterial adaptation to changing environmental conditions. In Mycobacterium tuberculosis, oxidative and acidic stresses as well as iron starvation induce rubredoxin expression. However, their functions during M. tuberculosis infection is unknown. In the present work, we show that rubredoxin B (RubB) supports catalytic activity of mycobacterial cytochrome P450s, CYP124, CYP125, and CYP142, which are important for bacterial viability and pathogenicity. We solved the crystal structure of RubB and characterized the interaction between RubB and CYPs using site-directed mutagenesis. Mutations that neutralized single charge on the surface of RubB did not dramatically decrease activity of studied CYPs, and isothermal calorimetry (ITC) experiments indicated that interactions are transient and not highly specific. Our findings suggest that a switch from ferredoxins to rubredoxins support CYP activity in M. tuberculosis-infected macrophages. Our electrochemical experiments suggest potential applications of RubB in biotechnology.