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Photochemical energy conversion during oxygenic photosynthesis is performed by membrane-embedded chlorophyll-binding protein complexes. The biogenesis and maintenance of these complexes requires auxiliary protein factors that optimize the assembly process and protect nascent complexes from photodamage. In cyanobacteria, several lipoproteins contribute to the biogenesis and function of the photosystem II (PSII) complex. They include CyanoP, CyanoQ, and Psb27, which are all attached to the lumenal side of PSII complexes. Here, we show that the lumenal Ycf48 assembly factor found in the cyanobacterium Synechocystis sp. PCC 6803 is also a lipoprotein. Detailed mass spectrometric analysis of the isolated protein supported by site-directed mutagenesis experiments indicates lipidation of the N-terminal C29 residue of Ycf48 and removal of three amino acids from the C-terminus. The lipobox sequence in Ycf48 contains a cysteine residue at the -3 position compared to Leu/Val/Ile residues found in the canonical lipobox sequence. The atypical Ycf48 lipobox sequence is present in most cyanobacteria but is absent in eukaryotes. A possible role for lipoproteins in the coordinated assembly of cyanobacterial PSII is discussed.

The evolution of novel traits can have important consequences for biological diversification. Novelties such as new structures are associated with changes in both genotype and phenotype that often lead to changes in ecological function. 1,2 New ecological opportunities provided by a novel trait can trigger subsequent trait modification or niche partitioning 3 ; however, the underlying mechanisms of novel trait diversification are still poorly understood. Here, we report that the innovation of a new chlorophyll (Chl) pigment, Chl d , by the cyanobacterium Acaryochloris marina was followed by the functional divergence of its light-harvesting complex. We identified three major photosynthetic spectral types based on Chl fluorescence properties for a collection of A. marina laboratory strains for which genome sequence data are available, 4,5 with shorter- and longer-wavelength types more recently derived from an ancestral intermediate phenotype. Members of the different spectral types exhibited extensive variation in the Chl-binding proteins as well as the Chl energy levels of their photosynthetic complexes. This spectral-type divergence is associated with differences in the wavelength dependence of both growth rate and photosynthetic oxygen evolution. We conclude that the divergence of the light-harvesting apparatus has consequently impacted A. marina ecological diversification through specialization on different far-red photons for photosynthesis. • Functional divergence of the light-harvesting complex of Acaryochloris marina • Three major photosynthetic spectral types identified by chlorophyll fluorescence • Short- and long-wavelength types recently derived from an ancestral intermediate • This resulted in specialization on different far-red wavelengths for photosynthesis The evolution of novel traits has important consequences for biological diversification. Ulrich et al. show that the innovation of a new chlorophyll pigment by a cyanobacterium was followed by the functional divergence of its light-harvesting complex to specialize on different far-red wavelengths for photosynthesis. [ABSTRACT FROM AUTHOR]

Chlorophyll (Chl) is indispensable for photosynthesis. In association with Chl-binding proteins (CBPs), it is responsible for light absorption, excitation energy transfer, and charge separation within the photosynthetic complexes. By contrast, photoexcitation of free Chl and its metabolic intermediates generates hazardous reactive oxygen species (ROS). While antagonistic activities of Chl synthesis and catabolism have been mostly elucidated, the tight synchronization of these metabolic activities with the formation and dismantling of the photosynthetic complexes is poorly understood. Recently, a set of auxiliary factors were identified to adjust metabolic activities and provide accurate amounts of Chl for pigment–protein complexes. Here, we review current knowledge of post-translational coordination of Chl formation, breakdown, and turnover with the assembly and disassembly of various CBPs and highlight future research perspectives. Optimal photosynthesis and proper leaf development rely on spatiotemporal regulation of Chl metabolism. Availability of Chl is crucial for the stability, correct folding, and membrane integration of CBPs; and Chl release occurs before the proteolysis of Chl-binding proteins. A conserved Chl assembly complex identified in arabidopsis (Arabidopsis thaliana) and cyanobacteria requires auxiliary factors, which may function either as Chl carriers or scaffold proteins that facilitate the integration of Chl into CBPs at the thylakoid membranes. A suite of post-translational regulators is implicated in the regulation of various aspects of Chl metabolism, and serve to coordinate the varying demand for Chl for biogenesis, maintenance, and degradation of the pigment–protein complexes. [ABSTRACT FROM AUTHOR]

Type‐II water‐soluble chlorophyll (Chl) proteins (WSCPs) of Brassicaceae are promising models for understanding how protein sequence and structure affect Chl binding and spectral tuning in photosynthetic Chl–protein complexes. However, to date, their use has been limited by the small number of known WSCPs, which also limited understanding their physiological roles. To overcome these limitations, we performed a phylogenetic analysis to compile a more comprehensive and complete set of natural type‐II WSCP homologues. The identified homologues were heterologously expressed in Escherichia coli, purified, tested for assembly with chlorophylls, and spectroscopically characterized. The analyses led to the discovery of previously unrecognized type‐IIa and IIb subclass WSCPs, as well as of a new subclass that did not bind chlorophylls. Further analysis by ancestral sequence reconstruction yielded sequences of putative ancestors of the three subclasses, which were subsequently recombinantly expressed in E. coli, purified and characterized. Combining the phylogenetic and spectroscopic data with molecular structural information revealed distinct Chl‐binding motifs, and identified residues critically impacting spectral tuning. The distinct Chl‐binding properties of the WSCP archetypes suggest that the non‐Chl‐binding subclass evolved from a Chl‐binding ancestor that most likely lost its Chl‐binding capacity upon localization in the plant tissues with low Chl content. This dual evolutionary trajectory is consistent with WSCPs association with the Kunitz‐type protease inhibitors superfamily, and indications of their inhibitory activity in response to various forms of stress in plants. These findings suggest new directions for exploring the physiological roles of WSCPs and the correlation, if any, between Chl‐binding and protease inhibition functionality. [ABSTRACT FROM AUTHOR]

Water soluble chlorophyll-binding proteins (WSCPs) of higher plants differ from most proteins containing chlorophyll or bacteriochlorophyll in that they are soluble in watr and are neither embedded in the lipid membrane nor directly involved in the process of photosynthesis. Chlorophyll molecules in WSCPs ensembles are packed in dimers within the hydrophobic zone of the protein matrix, similar to the structure of a chlorophyll "special pair" in the reaction centers of phototrophs. This fact together with the detected photosensitizing activity of WSCPs makes it possible to consider these proteins as a promising object for modelling the evolutionary prototypes of the photosynthetic apparatus, as well as for developing the artificial solar energy converters. There are two classes of proteins in the WSCP family, class I and class II the representatives of these classes have a weak degree of homology in the primary structure, but a high degree of similarity in the tertiary and quaternary structure. One of the features of class I WSCPs is photoconversion, that is, to change the structure and spectral properties of the chromophore under the action of light. The functions of WSCPs in the plant are thought to be associated with stress protection. [ABSTRACT FROM AUTHOR]

The light-harvesting chlorophyll a /b-binding (Lhc) superfamily, composed of several distinct antennae protein families, plays essential roles in light capture and photoprotection in plants. Compared with the extensive research in Arabidopsis thaliana and certain species, little is known about this superfamily in cassava (Manihot esculenta), an Euphorbiaceous plant experienced one so-called ρ recent whole-genome duplication (WGD). This study presents the first genome-wide identification of Lhc supergene family in cassava, resulting in 35 members that are distributed across 15 chromosomes. Phylogenetic analysis and BRH (Best Reciprocal Hit)-based sequence comparison assigned these genes into four previously defined families and 26 orthologous groups (including one absent from Arabidopsis). Synteny analysis showed that nine identified duplicates were derived from the WGD as well as local duplication, and retention bias of WGD duplicates in this species was shown to be something different from that in Arabidopsis which experienced two recent WGDs. Transcriptional profiling of MeLhc superfamily genes revealed a predominant expression pattern in green tissues such as leaf and midvein. Moreover, comparison of exon-intron structures, protein motifs, and gene expression profiles revealed divergence of duplicate pairs. Our findings will not only improve our knowledge on the evolution of this superfamily in cassava, but also provide valuable information for further functional studies. • This is the first genome-wide analysis of Lhc superfamily genes in cassava, an economically important Euphorbiaceous plant. • A high number of 35 members were found, which are unevenly distributed across 15 out of the 18 chromosomes. • Nine duplicates identified were shown to result from the so-called ρ recent WGD as well as local duplication. • Retention bias of WGD duplicates in cassava is different from Arabidopsis , a model plant experienced two recent WGDs. • Comparison of protein motifs and gene expression profiles revealed divergence of MeDof duplicates. [ABSTRACT FROM AUTHOR]

Background: Common buckwheat (Fagopyrum esculentum) is an important staple food crop in southwest China, where drought stress is one of the largest limiting factors that lead to decreased crop production. To reveal the molecular mechanism of common buckwheat in response to drought stress, we performed a comprehensive transcriptomics study to evaluate gene expression profiles of common buckwheat during PEG-mediated drought treatment. Results: In total, 45 million clean reads were assembled into 53,404 unigenes with an average length of 749 bp and N50 length of 1296 bp. A total of 1329 differentially expressed genes (DEGs) were identified by comparing wellwatered and drought-treated plants, out of which 666 were upregulated and 663 were downregulated. Furthermore, we defined the functional characteristics of DEGs using GO and KEGG classifications. GO enrichment analysis showed that the DEGs were significantly overrepresented in four categories, namely, "oxidoreductase activity," "oxidation-reduction process," "xyloglucan:xyloglucosyl transferase activity," and "apoplast." Using KEGG pathway analysis, a large number of annotated genes were overrepresented in terms such as "plant hormone signal transduction," "phenylpropanoid biosynthesis," "photosynthesis," and "carbon metabolism." Conclusions: These results can be further exploited to investigate the molecular mechanism of common buckwheat in response to drought treatment and could supply with valuable molecular sources for abiotic-tolerant elite breeding programs in the future. [ABSTRACT FROM AUTHOR]

Abstract Tobacco mosaic virus (TMV) is a positive single-stranded RNA virus. Its 5′ end ORF codes for the replicase proteins, namely 126 kDa and 183 kDa, respectively. These proteins interact with many host proteins to form a virus replication complex (VRC). This study aims to dissect the proteome profile of TMV-infected Nicotiana tabacum in host cellular and molecular pathways. We used the isobaric tags for relative and absolute quantification (iTRAQ) technique to analyse the differential global proteomic profile of TMV infected and mock infected plants. Out of 1897 total proteins, we identified 407 differentially abundant proteins and grouped them into three functional categories, namely metabolism, cellular processes and signalling processing. Our results showed that photosynthesis, carbon metabolism, plant defence, protein synthesis, and protein processing in the endoplasmic reticulum were significantly altered. Carbon metabolism and photosynthesis were present in very low abundance, whereas accumulation of reactive oxygen species and misfolded proteins lead to the accumulation of thioredoxin H-type 1. In conclusion, we identified several key host proteins that are involved in TMV infection/replication in N. tabacum plants. Significance of the study TMV is one of the most widely studied plant virus. It is used as a tool to study host-virus interaction. There are several host proteins reported that facilitate VRC formation and replication of TMV. However, there is limited knowledge in the expression regulation of these host proteins upon TMV infection. This study is the first report that investigates the response of host protein expression involved in TMV infection through a quantitative proteomics technique iTRAQ, combined with LC-MS/MS analysis. We used TMV-infected Nicotiana tabacum plants to investigate the effects of TMV infection on host proteins. Our results revealed differential abundance of proteins involving various pathways in protein translation, protein processing, photosynthesis and plant defence. There was a high abundance of thioredoxin H-type 1, a protein that counters oxidative stress and accelerated regulation of fatty acid synthesis to provide additional lipid molecules for VRC formation. There was a significant reduction in abundance of psaA and psbB proteins in the photosynthetic pathways. Our results identified key candidate host proteins involved in TMV-infected N. tabacum for functional studies in future. Highlights • Elevated thioredoxin H-type 1 protects TMV-infected plants from oxidative damage • Significant decrease in abundance of psaA and psbB in photosystems I and II • Increased fatty acid enzymes provide extra lipid molecules to build VRC scaffolds [ABSTRACT FROM AUTHOR]

Abstract—: A method using chromatography on DEAE-Toyopearl 650M was developed for the simultaneous extraction of water-soluble chromoproteins from Arthrospira platensis cyanobacteria cells. These chromoproteins were C-phycocyanin, allophycocyanin, and carotenoid- and chlorophyll-binding proteins. The purity of the isolated C-phycocyanin was 4.42 (A620/A280). The allophycocyanin purity was 3.40 (A652/A280). The phycocyanin purity was confirmed by the presence of only two bands obtained during SDS-PAGE: α-subunit (17 kDa) and β-subunit (18 kDa). The isolated carotenoid- and chlorophyll-binding proteins were analyzed by high-performance exclusion chromatography on TSK-GEL 2000SW (XL) with detection at three wavelengths (280, 480, and 678 nm). The spectral, chromatographic, and electrophoretic analyses of chromoproteins, as well as pigment analysis, made it possible to conclude that the carotenoid—chlorophyll a binding protein was a xanthophyll-chlorophyll a protein complex, and the chlorophyll a binding protein was a chlorophyll a protein complex. The molecular weight of the proteins was determined by high-performance exclusion chromatography and SDS-PAGE to be 57 and 16 kDa, respectively. The photoprotective properties of these proteins and their possible functioning as part of evolutionary precursors of photosynthetic systems are discussed. [ABSTRACT FROM AUTHOR]

Higher plant Photosystem I (PSI) includes a peripheral antenna system (LHCI) composed of four light-harvesting proteins (Lhca1-Lhca4). The LHCI system is highly conserved, suggesting that it plays a specific role within the LHC family. In order to elucidate the specific function of LHCI, the phenotype of an Arabidopsis mutant devoid of the whole LHCI system was studied over a range of conditions, including rapid changes in irradiation. ΔLhca plants displayed stunted growth and reduced thylakoid lumen acidification respect to wild type, suggesting that the lack of LHCI affected electron transport rate. Under rapidly changing light intensity, growth rate of the mutant was further reduced and the redox balance of the photosynthetic electron chain impaired. Instead, under constant, excess light regime, the ΔLhca plants did not suffer enhanced photooxidation vs. wild type, implying LHCI optimizes the flow rate through the electron transport chain by maintaining high PSI activity at all irradiances. We conclude that a complete PSI supercomplex, including LHCI, is crucial for the dynamic regulation of PQ redox state and therefore for PSII photoprotection. [ABSTRACT FROM AUTHOR]

Post-harvest mango decay is caused by multiple pathogens in tropical conditions but concerns regarding the risk of food contamination by fungicides established biocontrol as a promising alternative. However, occurrence of quiescent infections requires pre-harvest applications of biocontrol agents (BCA), exposing them to harmful UV radiation effects. The objective of this work was to evaluate UV sensitivity of yeast BCA strains previously selected against multiple pathogens that cause mango decay and evaluate suitable UV protectants. In a first bioassay conducted exposing yeast suspensions sprayed on glass plates, it was verified that Saccharomyces sp. ESA47 and Pichia kudriavzevii CMIAT171 were highly sensitive to UV, while Saccharomyces cerevisiae ESA45 had a slightly lower mortality. A bioassay using fragments of mango peels evaluated UV protection from increasing concentrations of starch, dextrin, casein, benzophenone, and cinnamic acid derivative compounds. Results showed that starch and isoamyl p-methoxycinnamate (NHE-1000) resulted in higher survival for yeast strains in doses of 10.0 and 1.0 g kg−1, respectively. Application of the yeast BCA in a semi-commercial mango orchard resulted in a significant reduction of post-harvest disease incidence and severity. Field application of the yeasts in technical grade preparations containing both UV protectants enhanced the control efficiency by 52.5, 31.9, and 37.7% for ESA45, ESA47, and CMIAT171, respectively. [ABSTRACT FROM AUTHOR]

Robust photosynthesis in chloroplasts and cyanobacteria requires the participation of accessory proteins to facilitate the assembly and maintenance of the photosynthetic apparatus located within the thylakoid membranes. The highly conserved Ycf48 protein acts early in the biogenesis of the oxygen-evolving photosystem II (PSII) complex by binding to newly synthesized precursor D1 subunit and by promoting efficient association with the D2 protein to form a PSII reaction center (PSII RC) assembly intermediate. Ycf48 is also required for efficient replacement of damaged D1 during the repair of PSII. However, the structural features underpinning Ycf48 function remain unclear. Here we show that Ycf48 proteins encoded by the thermophilic cyanobacterium Thermosynechococcus elongatus and the red alga Cyanidioschyzon merolae form seven-bladed beta-propellers with the 19-aa insertion characteristic of eukaryotic Ycf48 located at the junction of blades 3 and 4. Knowledge of these structures has allowed us to identify a conserved "Arg patch" on the surface of Ycf48 that is important for binding of Ycf48 to PSII RCs but also to larger complexes, including trimeric photosystem I (PSI). Reduced accumulation of chlorophyll in the absence of Ycf48 and the association of Ycf48 with PSI provide evidence of a more wide-ranging role for Ycf48 in the biogenesis of the photosynthetic apparatus than previously thought. Copurification of Ycf48 with the cyanobacterial YidC protein insertase supports the involvement of Ycf48 during the cotranslational insertion of chlorophyll-binding apopolypeptides into the membrane. [ABSTRACT FROM AUTHOR]

Fucoxanthin chlorophyll (Chl) a / c protein (FCP) is the major light-harvesting complex found in aquatic photosynthetic organisms such as diatoms and brown algae. In FCP, fucoxanthin and Chl- c absorb light in the blue-green region, and both of the antenna pigments transfer the excitation energy to Chl- a . Chl- c is characterized by the 17-acrylate moiety (17-CH CH COOH) conjugated to the porphyrin backbone, extending its π-conjugation. Protonation (17-CH CH COOH) or deprotonation (17-CH CH COO − ) of the acrylate moiety is capable of affecting the optical properties of Chl- c . In this study, we purified the FCP from Chaetoceros calcitrans , a diatom, and measured its electronic absorption, circular dichroism, fluorescence, and fluorescence-excitation spectra in buffer solutions at different pH values. A pH-dependent change was clearly observed at the Soret absorption band of Chl- c . Based on the change, the acid-dissociation constant of Chl- c , pKa, was determined to be 5.3 ± 0.2. Moreover, fluorescence spectroscopy revealed that a decrease in the energy transfer efficiency from Chl- c to Chl- a under acidic condition. The present results demonstrate that acid-dissociation of Chl- c occurs even while bound to FCP, thus giving a new insight into the photosynthetic function of Chl- c bound to the pigment-protein complexes. [ABSTRACT FROM AUTHOR]

The first step in chlorophyll a degradation is the extraction of the central Mg. This reaction is catalyzed by Mg-dechelatase encoded by Stay-Green ( SGR ) in land plants. SGR extracts Mg from chlorophyll a but not from chlorophyll b , and chlorophyll b must be converted to chlorophyll a before degradation. The first reaction of the chlorophyll b to chlorophyll a conversion is catalyzed by chlorophyll b reductase. Non-Yellow Coloring 1 (NYC1) and NYC1 like (NOL) are isozymes of chlorophyll b reductase. When SGR was transiently overexpressed in Arabidopsis , both chlorophyll a and b were degraded, suggesting that the chlorophyll b to chlorophyll a conversion is activated by SGR overexpression. To examine the involvement of chlorophyll b reductases in SGR-induced chlorophyll b degradation, SGR was transiently overexpressed in nyc1 , nol , and nyc1 nol double mutants by dexamethasone treatment. It was found that in the wild type and nol mutant, chlorophyll a and b were degraded and all the chlorophyll-binding proteins decreased. Meanwhile, in nyc1 and nyc1 nol mutants, chlorophyll b degradation was suppressed and the light-harvesting complex of photosystem II remained. The mRNA and protein levels of NYC1 increased after SGR overexpression in wild type plants. These results suggest that Mg-dechelation of chlorophyll a by SGR activates chlorophyll b degradation by inducing the expression of NYC1 . This is an effective regulation of a metabolic pathway. [ABSTRACT FROM AUTHOR]

Photosystem I (PSI) has evolved in anaerobic atmospheric conditions and until today remains susceptible to oxygen. To minimize the probability of damaging side reactions, plants have evolved sophisticated mechanisms to control electron transfer, and PSI becomes inhibited only when malfunctions of these regulatory mechanisms occur. Because of the complicated induction of PSI photoinhibition, a detailed investigation into the process and following reactions are still largely missing. Here, we introduce the theoretical framework and a novel method for an easy and controlled induction of PSI photoinhibition in vivo. The method mimics the PSI damage mechanisms of fluctuating light‐sensitive mutant plants (stn7, pgr5) which cannot control electron donation to PSI. Because PSII and PSI have different light absorption properties, electrons accumulate in the intersystem electron transfer chain (ETC), if PSII is preferentially excited. A saturating light pulse given upon an over‐reduced ETC leads to the saturation of PSI electron acceptors, ultimately leading to the production of reactive oxygen species and photoinhibition of PSI. By adjusting the time of the light treatment, PSI can be gradually photoinhibited, providing a novel tool to holistically investigate the PSI photoinhibition phenomenon. [ABSTRACT FROM AUTHOR]

The special-pair chlorophyll (Chl) P680 in photosystem II has an extremely high redox potential (Em) to enable water oxidation in photosynthesis. Significant positive-charge localization on one of the Chl constituents, PD1 or PD2, in P680+ has been proposed to contribute to this high Em. To identify the Chl molecule on which the charge is mainly localized, we genetically introduced a hydrogen bond to the 131-keto C=O group of PD1 and PD2 by changing the nearby D1-Val-157 and D2-Val-156 residues to His, respectively. Successful hydrogen bond formation at PD1 and PD2 in the obtained D1-V157H and D2-V156H mutants, respectively, was monitored by detecting 131-keto C=O vibrations in Fourier transfer infrared (FTIR) difference spectra upon oxidation of P680 and the symmetrically located redox-active tyrosines YZ and YD, and they were simulated by quantum-chemical calculations. Analysis of the P680+/P680 FTIR difference spectra of D1-V157H and D2-V156H showed that upon P680+ formation, the 131-keto C=O frequency upshifts by a much larger extent in PD1 (23 cm-1) than in PD2 (<9 cm-1). In addition, thermoluminescence measurements revealed that the D1-V157H mutation increased the Em of P680 to a larger extent than did the D2-V156H mutation. These results, together with the previous results for the mutants of the His ligands of PD1 and PD2, lead to a definite conclusion that a charge is mainly localized to PD1 in P680+. [ABSTRACT FROM AUTHOR]

Chlorophyll is an indispensable constituent of the photosynthetic machinery in green organisms. Bound by apoproteins of photosystems I and II, chlorophyll performs lightharvesting and charge separation. Due to the phototoxic nature of free chlorophyll and its precursors, chlorophyll synthesis is regulated to comply with the availability of nascent chlorophyll-binding apoproteins. Conversely, the synthesis and co-translational insertion of such proteins into the thylakoid membrane have been suggested to be influenced by chlorophyll availability. In this study, we addressed these hypotheses by using ribosome profiling to examine the synthesis and membrane targeting of chlorophyll-binding apoproteins in chlorophyll-deficient chlH maize mutants (Zm-chlH). ChlH encodes the H subunit of the magnesium chelatase (also known as GUN5), which catalyzes the first committed step in chlorophyll synthesis. Our results show that the number and distribution of ribosomes on plastid mRNAs encoding chlorophyllbinding apoproteins are not substantially altered in Zm-chlH mutants, suggesting that chlorophyll has no impact on ribosome dynamics. Additionally, a Zm-chlH mutation does not change the amino acid position at which nascent chlorophyll-binding apoproteins engage the thylakoid membrane, nor the efficiency with which membrane-engagement occurs. Together, these results provide evidence that chlorophyll availability does not selectively activate the translation of plastid mRNAs encoding chlorophyll apoproteins. Our results imply that co- or post-translational proteolysis of apoproteins is the primary mechanism that adjusts apoprotein abundance to chlorophyll availability in plants. [ABSTRACT FROM AUTHOR]

This paper presents spectroscopic investigations of IsiA, a chlorophyll a -binding membrane protein produced by cyanobacteria grown in iron-deficient environments. IsiA, if associated with photosystem I, supports photosystem I in light harvesting by efficiently transferring excitation energy. However, if separated from photosystem I, IsiA exhibits considerable excitation quenching observed as a substantial reduction of protein-bound chlorophyll a fluorescence lifetime. Previous spectroscopic studies suggested that carotenoids are involved in excitation energy dissipation and in addition play a second role in this antenna complex by supporting chlorophyll a in light harvesting by absorbing in the spectral range inaccessible for chlorophyll a and transferring excitation to chlorophylls. However, this investigation does not support these proposed roles of carotenoids in this light harvesting protein. This study shows that carotenoids do not transfer excitation energy to chlorophyll a . In addition, our investigations do not support the hypothesis that carotenoids are quenchers of the excited state of chlorophyll a in this protein complex. We propose that quenching of chlorophyll a fluorescence in IsiA is maintained by pigment-protein interaction via electron transfer from an excited chlorophyll a to a cysteine residue, an excitation quenching mechanism that was recently proposed to regulate the light harvesting capabilities of the bacteriochlorophyll a -containing Fenna-Mathews-Olson protein from green sulfur bacteria. [ABSTRACT FROM AUTHOR]

In this study, we used the biosynthetic inhibitors of carotenoid and tetrapyrrole biosynthetic pathways, norflurazon (NF) and oxyfluorfen (OF), as tools to gain insight into mechanisms of photooxidation in rice plants. NF resulted in bleaching symptom on leaves of the treated plants, whereas OF treatment developed a fast symptom of an apparent necrotic phenotype. Both plants exhibited decreases in photosynthetic efficiency, as indicated by F v /F m . NF caused severe disruption in thylakoid membranes, whereas OF-treated plants exhibited disruption of chloroplast envelope and plasma membrane. Levels of Lhca and Lhcb proteins in photosystem I (PSI) and PSII were reduced by photooxidative stress in NF- and OF-treated plants, with a greater decrease in NF plants. The down-regulation of nuclear-encoded photosynthesis genes Lhcb and rbcS was also found in both NF- and OF-treated plants, whereas plastid-encoded photosynthetic genes including RbcL , PsaC , and PsbD accumulated normally in NF plants but decreased drastically in OF plants. This proposes that the plastids in NF plants retain their potential to develop thylakoid membranes and that photobleaching is mainly controlled by nuclear genes. Distinct photooxidation patterns between NF- and OF-treated plants developed differential signaling, which might enable the plant to coordinate the expression of photosynthetic genes from the nuclear and plastidic genomes. [ABSTRACT FROM AUTHOR]

The hydrophilic water-soluble chlorophyll binding proteins (WSCP) which form complex with chlorophyll molecules have been numerously isolated from the chloroplasts of plants. Although, their molecular properties have been partly characterized, but their physio-biochemical roles are still unclear in the photosynthesizing organs. In this study, using bioinformatic tools WSCP pair were predicted to act as hydrolase and hydrolase inhibitor towards chlorophyll molecules. To enhance our information regarding the possible functions of WSCP, we cloned WSCP1 and WSCP2 cDNAs from Chenopodium album L. and Brassica oleracea L. leaves and expressed them as soluble maltose-binding fusion proteins in Escherichia coli. The purified fused products were subjected to chlorophyll hydrolyzing activity in vitro. The results showed that WSCP1 and WCSP2 are antagonistically involved in chlorophyll breakdown, while WSCP1 acts as chlorophyll hydrolyzing enzyme (with the hydrolysis rate of about 40% per 12 h), WSCP2 exerts inhibitory activity (with the inhibition rate of about 38% per 12 h) towards chlorophyll hydrolysis. This is the first ever time report speculates the hydrolase/inhibitory roles for WSCP and proposes that the relative activity of WSCP pair might balance and regulate the chlorophyll breakdown process in the photosynthetic apparatus of plants. It may open the new gate to investigate the potent roles of WSCP in plant system. [ABSTRACT FROM AUTHOR]

Artificial photosynthesis-reduction of CO2 into chemicals and fuels with water oxidation in the presence of sunlight as the energy source-mimics natural photosynthesis in green plants, and is considered to have a significant part to play in future energy supply and protection of our environment. The high quantum efficiency and easy manipulation of heterogeneous molecular photosystems based on metal complexes enables them to act as promising platforms to achieve efficient conversion of solar energy. This Review describes recent developments in the heterogenization of such photocatalysts. The latest state-of-the-art approaches to overcome the drawbacks of low durability and inconvenient practical application in homogeneous molecular systems are presented. The coupling of photocatalytic CO2 reduction with water oxidation through molecular devices to mimic natural photosynthesis is also discussed. [ABSTRACT FROM AUTHOR]

Main conclusion : The photosystem I/II ratio increased when antenna size was enlarged by transient induction of CAO in chlorophyll b -less mutants, thus indicating simultaneous regulation of antenna size and photosystem I/II stoichiometry. Regulation of antenna size and photosystem I/II stoichiometry is an indispensable strategy for plants to acclimate to changes to light environments. When plants grown in high-light conditions are transferred to low-light conditions, the peripheral antennae of photosystems are enlarged. A change in the photosystem I/II ratio is also observed under the same light conditions. However, our knowledge of the correlation between antenna size modulation and variation in photosystem I/II stoichiometry remains limited. In this study, chlorophyll a oxygenase was transiently induced in Arabidopsis thaliana chlorophyll b-less mutants, ch1- 1, to alter the antenna size without changing environmental conditions. In addition to the accumulation of chlorophyll b, the levels of the peripheral antenna complexes of both photosystems gradually increased, and these were assembled to the core antenna of both photosystems. However, the antenna size of photosystem II was greater than that of photosystem I. Immunoblot analysis of core antenna proteins showed that the number of photosystem I increased, but not that of photosystem II, resulting in an increase in the photosystem I/II ratio. These results clearly indicate that antenna size adjustment was coupled with changes in photosystem I/II stoichiometry. Based on these results, the physiological importance of simultaneous regulation of antenna size and photosystem I/II stoichiometry is discussed in relation to acclimation to light conditions. [ABSTRACT FROM AUTHOR]

The chlorophyll -binding protein (CAB) serves in both photosystems (PS), I and II, as a coordinator of antenna pigments in the light-harvesting complex (LHC). The CABs constitute abundant and important proteins in the thylakoid membrane of higher plants. In our study, five CAB genes, which contained full-length cDNA sequences from the 4-year-old ginseng leaves ( Panax ginseng Meyer), were isolated and named PgCAB. Phylogenetic comparison of the members of the subfamily between ginseng and higher plants, including Arabidopsis, revealed that the putative functions of these ginseng CAB proteins were clustered into the different family of Arabidopsis CABs; two PgCABs in LHCII family and three PgCABs in LHCI family. The expression analysis of PgCABs consistently showed dark-dependent inhibition in leaves. Expression analysis during abiotic stress identified that PgCAB genes responded to heavy metal, salinity, chilling, and UV stresses differently, suggesting their specific function during photosynthesis. This is the first comprehensive study of the CAB gene family in P. ginseng. [ABSTRACT FROM AUTHOR]

Etioplasts lack thylakoid membranes and photosystem complexes. Light triggers differentiation of etioplasts into mature chloroplasts, and photosystem complexes assemble in parallel with thylakoid membrane development. Plastids isolated at various time points of de-etiolation are ideal to study the kinetic biogenesis of photosystem complexes during chloroplast development. Here, we investigated the chronology of photosystem II (PSII) biogenesis by monitoring assembly status of chlorophyll-binding protein complexes and development of water splitting via O2 production in plastids (etiochloroplasts) isolated during de-etiolation of barley ( Hordeum vulgare L.). Assembly of PSII monomers, dimers and complexes binding outer light-harvesting antenna [PSII-light-harvesting complex II (LHCII) supercomplexes] was identified after 1, 2 and 4 h of de-etiolation, respectively. Water splitting was detected in parallel with assembly of PSII monomers, and its development correlated with an increase of bound Mn in the samples. After 4 h of de-etiolation, etiochloroplasts revealed the same water-splitting efficiency as mature chloroplasts. We conclude that the capability of PSII to split water during de-etiolation precedes assembly of the PSII-LHCII supercomplexes. Taken together, data show a rapid establishment of water-splitting activity during etioplast-to-chloroplast transition and emphasize that assembly of the functional water-splitting site of PSII is not the rate-limiting step in the formation of photoactive thylakoid membranes. [ABSTRACT FROM AUTHOR]

The ability to tune the light-absorption properties of chlorophylls by their protein environment is the key to the robustness and high efficiency of photosynthetic light-harvesting proteins. Unfortunately, the intricacy of the natural complexes makes it very difficult to identify and isolate specific protein-pigment interactions that underlie the spectral-tuning mechanisms. Herein we identify and demonstrate the tuning mechanism of chlorophyll spectra in type II water-soluble chlorophyll binding proteins from Brassicaceae (WSCPs). By comparing the molecular structures of two natural WSCPs we correlate a shift in the chlorophyll red absorption band with deformation of its tetrapyrrole macrocycle that is induced by changing the position of a nearby tryptophan residue. We show by a set of reciprocal point mutations that this change accounts for up to 2/3 of the observed spectral shift between the two natural variants. [ABSTRACT FROM AUTHOR]

In the chlorophyll (Chl) biosynthesis pathway the formation of protochlorophyllide is catalyzed by Mg-protoporphyrin IX methyl ester (MgPME) cyclase. The Ycf54 protein was recently shown to form a complex with another component of the oxidative cyclase, Sll1214 (CycI), and partial inactivation of the ycf54 gene leads to Chl deficiency in cyanobacteria and plants. The exact function of the Ycf54 is not known, however, and further progress depends on construction and characterization of a mutant cyanobacterial strain with a fully inactivated ycf54 gene. Here, we report the complete deletion of the ycf54 gene in the cyanobacterium Synechocystis 6803; the resulting Δycf54 strain accumulates huge concentrations of the cyclase substrate MgPME together with another pigment, which we identified using nuclear magnetic resonance as 3-formyl MgPME. The detection of a small amount (~13%) of Chl in the Δycf54 mutant provides clear evidence that the Ycf54 protein is important, but not essential, for activity of the oxidative cyclase. The greatly reduced formation of protochlorophyllide in the Δycf54 strain provided an opportunity to use 35S protein labeling combined with 2D electrophoresis to examine the synthesis of all known Chl-binding protein complexes under drastically restricted de novo Chl biosynthesis. We show that although the Δycf54 strain synthesizes very limited amounts of photosystem I and the CP47 and CP43 subunits of photosystem II (PSII), the synthesis of PSII D1 and D2 subunits and their assembly into the reaction centre (RCII) assembly intermediate were not affected. Furthermore, the levels of other Chl complexes such as cytochrome b6f and the HliD--Chl synthase remained comparable to wild-type. These data demonstrate that the requirement for de novo Chl molecules differs completely for each Chl-binding protein. Chl traffic and recycling in the cyanobacterial cell as well as the function of Ycf54 are discussed. [ABSTRACT FROM AUTHOR]

A theory for the calculation of resonant and nonresonant hole-burning (HB) spectra of pigment-protein complexes is presented and applied to the water-soluble chlorophyll-binding protein (WSCP) from cauliflower. The theory is based on a non-Markovian line shape theory (Renger and Marcus J. Chem. Phys. 2002, 116, 9997) and includes exciton delocalization, vibrational sidebands, and lifetime broadening. An earlier approach by Reppert (J. Phys. Chem. Lett. 2011, 2, 2716) is found to describe nonresonant HB spectra only. Here we present a theory that can be used for a quantitative description of HB data for both nonresonant and resonant burning conditions. We find that it is important to take into account the excess energy of the excitation in the HB process. Whereas excitation of the zero-phonon transition of the lowest exciton state, that is, resonant burning allows the protein to access only its conformational substates in the neighborhood of the preburn state, any higher excitation gives the protein full access to all conformations present in the original inhomogeneous ensemble. Application of the theory to recombinant WSCP from cauliflower, reconstituted with chlorophyll a or chlorophyll b, gives excellent agreement with experimental data by Pieper et al. (J. Phys. Chem. B 2011, 115, 4053) and allows us to obtain an upper bound of the lifetime of the upper exciton state directly from the HB experiments in agreement with lifetimes measured recently in time domain 2D experiments by Alster et al. (J. Phys. Chem. B 2014, 118, 3524). [ABSTRACT FROM AUTHOR]

The peridinin-chlorophyll a -protein (PCP) is one of the major light harvesting complexes (LHCs) in photosynthetic dinoflagellates. We analyzed the oligomeric state of PCP isolated from the dinoflagellate Symbiodinium , which has received increasing attention in recent years because of its role in coral bleaching. Size-exclusion chromatography (SEC) and small angle neutron scattering (SANS) analysis indicated PCP exists as monomers. Native mass spectrometry (native MS) demonstrated two oligomeric states of PCP, with the monomeric PCP being dominant. The trimerization may not be necessary for PCP to function as a light-harvesting complex. [ABSTRACT FROM AUTHOR]

Chloroplasts utilize photons from solar radiation to synthesize energy-rich molecules of ATPs and NADPHs, which are further used in active cellular processes. Multiprotein complexes (MPCs), including photosystems (PSII and PSI), and the cellular architecture responsible for generation of the proton motive force and the subsequent photophosphorylation, mediate the task of ATP and NADPH synthesis. Both photosystems and other multiprotein assemblies are embedded in thylakoid membranes. Advances in techniques used to study structural biology, biophysics, and comparative genomics and proteomics have enabled us to gain insights of structure, function, and localization of each individual component of the photosynthetic apparatus. An efficient coordination among MPCs is essential for normal functioning of photosynthesis, but there are various stressors that might directly or indirectly interact with photosynthetic components and processes. Cadmium is one of the toxic heavy metals that interact with photosynthetic components and damage photosystems and other MPCs in thylakoids. In plants, iron deficiency shows similar symptoms as those caused by Cd. Our article provides a general overview of chloroplast structure and a critical account of Cd-induced changes in photosystems and other MPCs in thylakoids, and suggests the possible mechanisms involved in mediating these changes. The connection between Cd-induced Fe deficiency and the elevated Cd toxicity under the Fe-deficient condition was also discussed. [ABSTRACT FROM AUTHOR]

Styrene-maleic acid copolymer was used to effect a non-detergent partial solubilization of thylakoids from spinach. A high density membrane fraction, which was not solubilized by the copolymer, was isolated and was highly enriched in the Photosystem (PS) I-light-harvesting chlorophyll (LHC) II supercomplex and depleted of PS II, the cytochrome b6/f complex, and ATP synthase. The LHC II associated with the supercomplex appeared to be energetically coupled to PS I based on 77 K fluorescence, P700 photooxidation, and PS I electron transport light saturation experiments. The chlorophyll (Chl) a/b ratio of the PS I-LHC II membranes was 3.2 ± 0.9, indicating that on average, three LHC II trimers may associate with each PS I. The implication of these findings within the context of higher plant PS I antenna organization is discussed. [ABSTRACT FROM AUTHOR]

The YidC/Alb3/Oxa1 family functions in the insertion and folding of proteins in the bacterial cytoplasmic membrane, the chloroplast thylakoid membrane, and the mitochondrial inner membrane. All members share a conserved region composed of five transmembrane regions. These proteins mediate membrane insertion of an assorted group of proteins, ranging from respiratory subunits in the mitochondria and light-harvesting chlorophyll-binding proteins in chloroplasts to ATP synthase sub-units in bacteria. This review discusses the YidC/Alb3/Oxa1 protein family as well as their function in membrane insertion and two new structures of the bacterial YidC, which suggest a mechanism for membrane insertion by this family of insertases. [ABSTRACT FROM AUTHOR]

Non-photosynthetic and hydrophilic chlorophyll ( Chl) proteins, called water-soluble Chl-binding proteins ( WSCPs), are distributed in various species of Chenopodiaceae, Amaranthaceae, Polygonaceae and Brassicaceae. Based on their photoconvertibility, WSCPs are categorised into two classes: Class I (photoconvertible) and Class II (non-photoconvertible). Chenopodium album WSCP ( Ca WSCP; Class I) is able to convert the chlorin skeleton of Chl a into a bacteriochlorin-like skeleton under light in the presence of molecular oxygen. Potassium iodide ( KI) is a strong inhibitor of the photoconversion. Because KI attacks tyrosine residues in proteins, tyrosine residues in Ca WSCP are considered to be important amino acid residues for the photoconversion. Recently, we identified the gene encoding Ca WSCP and found that the mature region of Ca WSCP contained four tyrosine residues: Tyr13, Tyr14, Tyr87 and Tyr134. To gain insight into the effect of the tyrosine residues on the photoconversion, we constructed 15 mutant proteins (Y13A, Y14A, Y87A, Y134A, Y13-14A, Y13-87A, Y13-134A, Y14-87A, Y14-134A, Y87-134A, Y13-14-87A, Y13-14-134A, Y13-87-134A, Y14-87-134A and Y13-14-87-134A) using site-directed mutagenesis. Amazingly, all the mutant proteins retained not only chlorophyll-binding activity, but also photoconvertibility. Furthermore, we found that KI strongly inhibited the photoconversion of Y13-14-87-134A. These findings indicated that the four tyrosine residues are not essential for the photoconversion. [ABSTRACT FROM AUTHOR]

The article focuses on a research on genes encoding for photoconvertible water-soluble chlorophyll-binding proteins (WSCPs). Topics discussed include identification of Chenopodium album WSCP (CaWSCP) as the chorophyll binding protein, analysis of spectral changes for Class I WSCPs using a primer set of untranslated regions (UTRs) and, expression of CfWSCP1-His and CfWSCP2-His as Class I WSCPs in C. ficifolium.

The article discusses research which reports importance of Cysteine-2 and Cys30 for chlorophyll-binding activity of the water-soluble chlorophyll-binding protein (WSCP) of Chenopodium album. Topics discussed include presence of non-photosynthetic chlorophyll protein WSCP in Chenopodium, ability of WSCP to photoconvert the chlorin skeleton of chlorophyll a into bacteriochlorin and generation of mutants by site-directed mutagenesis for identifying involvement of Cysteine in photoconversion.

An extraordinarily precise regulation of chlorophyll biosynthesis is essential for plant growth and development. However, our knowledge on the complex regulatory mechanisms of chlorophyll biosynthesis is very limited. Previous studies have demonstrated that miR171-targeted scarecrow-like proteins (SCL6/22/27) negatively regulate chlorophyll biosynthesis via an unknown mechanism. Here we showed that SCLs inhibit the expression of the key gene encoding protochlorophyllide oxidoreductase (POR) in light-grown plants, but have no significant effect on protochlorophyllide biosynthesis in etiolated seedlings. Histochemical analysis of β-glucuronidase (GUS) activity in transgenic plants expressing pSCL27::rSCL27-GUS revealed that SCL27-GUS accumulates at high levels and suppresses chlorophyll biosynthesis at the leaf basal proliferation region during leaf development. Transient gene expression assays showed that the promoter activity of PORC is indeed regulated by SCL27. Consistently, chromatin immunoprecipitation and quantitative PCR assays showed that SCL27 binds to the promoter region of PORC in vivo. An electrophoretic mobility shift assay revealed that SCL27 is directly interacted with G(A/G)(A/T)AA(A/T)GT cis-elements of the PORC promoter. Furthermore, genetic analysis showed that gibberellin (GA)-regulated chlorophyll biosynthesis is mediated, at least in part, by SCLs. We demonstrated that SCL27 interacts with DELLA proteins in vitro and in vivo by yeast-two-hybrid and coimmunoprecipitation analysis and found that their interaction reduces the binding activity of SCL27 to the PORC promoter. Additionally, we showed that SCL27 activates MIR171 gene expression, forming a feedback regulatory loop. Taken together, our data suggest that the miR171-SCL module is critical for mediating GA-DELLA signaling in the coordinate regulation of chlorophyll biosynthesis and leaf growth in light. [ABSTRACT FROM AUTHOR]

Water-solublechlorophyll-binding proteins (WSCPs) are interestingmodel systems for the study of pigment–pigment and pigment–proteininteractions. While class IIa WSCP has been extensively studied byspectroscopic and theoretical methods, a comprehensive spectroscopicstudy of class IIb WSCP was lacking so far despite the fact that itsstructure was determined by X-ray crystallography. In this paper,results of two-dimensional electronic spectroscopy applied to theclass IIb WSCP from Lepidium virginicumare presented.Global analysis of 2D data allowed determination of energy levelsand excitation energy transfer pathways in the system. Some additionalpathways, not present in class IIa WSCP, were observed. The data wereinterpreted in terms of a model comprising two interacting chlorophylldimers. In addition, oscillatory signals were observed and identifiedas coherent beatings of vibrational origin. [ABSTRACT FROM AUTHOR]

A hydroponic, greenhouse experiment was conducted to assess the effects of NaCl on growth, gas-exchange parameters, chlorophyll (Chl) content, and ion distribution in seven sesame ( Sesamum indicum L.) genotypes (Ardestan, Varamin, Naz-Takshakhe, Naz-Chandshakhe, Oltan, Yekta, Darab). The plants were grown in 4-L containers and subjected to varying levels of salinity (0, 30, and 60 mM NaCl). After 42 days, salt treatments induced decreases of plant fresh and dry mass, total leaf area, and plant height in all genotypes. Increasing NaCl concentration caused significant, genotypedependent decrease in the net photosynthetic rate, stomatal conductance, Chl content, and maximum quantum efficiency of photosystem II, while it increased the intercellular CO concentration. Based on the dry matter accumulation under salinity, the genotypes were categorized in two groups, i.e., salt-tolerant and salt-sensitive. The impact of salt on plant ion concentrations differed significantly among the sesame genotypes and between both two groups. The plant Na concentrations were significantly lower in Ardestan, Darab, and Varamin genotypes than those found in the remaining genotypes. The highest plant K and Ca concentrations together with the lowest Na/K and Na/Ca ratios were observed in Ardestan, Varamin, and Darab genotypes. Our results indicated the presence of differences in salt response among seven sesame genotypes. It suggested that growth and photosynthesis could depend on ion concentrations and ratios in sesame. [ABSTRACT FROM AUTHOR]

Seedlings of the hypoxia-sensitive cucumber cultivar were hydroponically grown under hypoxia for 7 d in the presence or absence of 24-epibrassinolide (EBR, 2.1 nM). Hypoxia significantly inhibited growth, while EBR partially counteracted this inhibition. Leaf net photosynthetic rate ( P), stomatal conductance, transpiration rate, and water-use efficiency declined greatly, while the stomatal limitation value increased significantly. The maximum net photosynthetic rate was strongly reduced by hypoxia, indicating that stomatal limitation was not the only cause of the P decrease. EBR markedly diminished the harmful effects of hypoxia on P as well as on stomata openness. It also greatly stimulated CO fixation by the way of increasing the carboxylation capacity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), ribulose-1,5-bisphosphate regeneration, Rubisco activity, and the protection of Rubisco large subunit from degradation. Our data indicated that photosystem (PS) II was damaged by hypoxia, while EBR had the protective effect. EBR further increased nonphotochemical quenching that could reduce photodamage of the PSII reaction center. The proportion of absorbed light energy allocated for photochemical reaction (P) was reduced, while both nonphotochemical reaction dissipation of light energy and imbalanced partitioning of excitation energy between PSI and PSII increased. EBR increased P and alleviated this imbalance. The results suggest that both stomatal and nonstomatal factors limited the photosynthesis of cucumber seedlings under hypoxia. EBR alleviated the growth inhibition by improving CO asimilation and protecting leaves against PSII damage. [ABSTRACT FROM AUTHOR]

The effect of ultraviolet B radiation (UV-B) on cellular ultrastructure, chlorophyll (Chl), carotenoids, and total phenolics of Acrostichum danaeifolium gametophytes was analyzed. The control group of spores was germinated under standard conditions, while the test group of spores was germinated with additional UV-B for 30 min every day for 34 d. The cell characteristics were preserved in gametophytes irradiated with UV-B, but the number of starch grains increased in the chloroplasts and the more developed grana organization in contrast to the chloroplasts of the control group. Chl a content decreased, while Chl b content increased in the gametophytes cultivated with UV-B for 34 d. Contents of lutein and zeaxanthin decreased and trans-β-carotene concentration was enhanced in the gametophytes irradiated with UV-B. The content of total phenolic compounds increased in the gametophytes cultivated with UV-B. Therefore our data suggest that the gametophytes of A. danaeifolium, a fern endemic to the mangrove biome, were sensitive to enhancement of UV-B radiation at the beginning of their development and they exhibited alterations in their ultrastructure, pigment contents, and protective mechanisms of the photosynthetic apparatus, when exposed to this radiation. [ABSTRACT FROM AUTHOR]

Alkalies are important agricultural contaminants complexly affecting plant metabolism. In this study, rice seedlings were subjected to alkaline stress (NaHCO:NaCO = 9:1; pH 8.9) for 30 days. The results showed that stress mightily reduced net photosynthetic rate ( P), but slightly decreased transpiration rate and stomatal conductance. This indicated that decline of P might be a result of nonstomatal factors. Alkaline stress caused a large accumulation of Na in leaves up to toxic concentration, which possibly affected chloroplast ultrastructure and photosynthesis. We found that alkaline stress reduced chlorophyll fluorescence parameters, such as ratios of F′/F′, F/F, photosystem (PS) II efficiency, and electron transport rates in rice plants, i.e. it influenced the efficiencies of photon capture and electron transport by PSII. This might be a main reason for the decrease of P under such conditions. Deficiency of minerals could be another reason for the decline of P. Alkaline stress lowered contents of N, K, Cu, Zn, P, and Fe in rice plants. In addition, the stress strongly affected metabolism of amino acids. This might be caused by imbalance in carbon metabolism as a result of photosynthesis reduction. [ABSTRACT FROM AUTHOR]

Chlorophyll (Chl) is an essential component of the photosynthetic apparatus. Embedded into Chl-binding proteins, Chl molecules play a central role in light harvesting and charge separation within the photosystems. It is critical for the photosynthetic cell to not only ensure the synthesis of a sufficient amount of new Chl-binding proteins but also avoids any misbalance between apoprotein synthesis and the formation of potentially phototoxic Chl molecules. According to the available data, Chl-binding proteins are translated on membrane bound ribosomes and their integration into the membrane is provided by the SecYEG/Alb3 translocon machinery. It appears that the insertion of Chl molecules into growing polypeptide is a prerequisite for the correct folding and finishing of Chl-binding protein synthesis. Although the Chl biosynthetic pathway is fairly well-described on the level of enzymatic steps, a link between Chl biosynthesis and the synthesis of apoproteins remains elusive. In this review, I summarize the current knowledge about this issue putting emphasis on protein-protein interactions. I present a model of the Chl biosynthetic pathway organized into a multi-enzymatic complex and physically attached to the SecYEG/Alb3 translocon. Localization of this hypothetical large biosynthetic centre in the cyanobacterial cell is also discussed as well as regulatory mechanisms coordinating the rate of Chl and apoprotein synthesis. [ABSTRACT FROM AUTHOR]

Various plants possess non-photosynthetic, hydrophilic chlorophyll (Chl) proteins called water-soluble Chl-binding proteins (WSCPs). WSCPs are categorized into two classes; Class I (photoconvertible type) and Class II (non-photoconvertible type). Among Class II WSCPs, only Lepidium virginicum WSCP (LvWSCP) exhibits a low Chl a/ b ratio compared with that found in the leaf. Although the physicochemical properties of LvWSCP have been characterized, its molecular properties have not yet been documented. Here, we report the characteristics of the LvWSCP gene, the biochemical properties of a recombinant LvWSCP, and the intracellular localization of LvWSCP. The cloned LvWSCP gene possesses a 669-bp open reading frame. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis revealed that the precursor of LvWSCP contains both N- and C-terminal extension peptides. RT-PCR analysis revealed that LvWSCP was transcribed in various tissues, with the levels being higher in developing tissues. A recombinant LvWSCP and hexa-histidine fusion protein (LvWSCP-His) could remove Chls from the thylakoid in aqueous solution and showed an absorption spectrum identical to that of native LvWSCP. Although LvWSCP-His could bind both Chl a and Chl b, it bound almost exclusively to Chl b when reconstituted in 40 % methanol. To clarify the intracellular targeting functions of the N- and C-terminal extension peptides, we constructed transgenic Arabidopsisthaliana lines expressing the Venus protein fused with the LvWSCP N- and/or C-terminal peptides, as well as Venus fused at the C-terminus of LvWSCP. The results showed that the N-terminal peptide functioned in ER body targeting, while the C-terminal sequence did not act as a trailer peptide. [ABSTRACT FROM AUTHOR]

Two enzymes, BciA and BciB, are known to reduce the C-8 vinyl group of 8-vinyl protochlorophyllide, producing protochlorophyllide a, during the synthesis of chlorophylls and bacteriochlorophylls in chlorophototrophic bacteria. BdA from the green sulfur bacterium Chlorobaculum tepidum reduces the C-8 vinyl group using NADPH as the reductant. Cyanobacteria and some other chlorophototrophs have a second, nonhomologous type of 8-vinyl reductase, BciB, but the biochemical properties of this enzyme have not yet been described. In this study, the btiB gene of the green sulfur bacterium Chloroherpeton thalassium was expressed in Escherichia coli, and the recombinant protein was purified and characterized- Recombinant BciB binds a flavin adenine dinucleoride cofactor, and EPR spectroscopy as well as quantitative analyses of bound iron and sulfide suggest that BciB binds two [4Fe-4S] clusters, one of which may not be essential for the activity of the enzyme. Using electrons provided by reduced ferredoxin or dithionite, recombinant BciB was active and reduced the 8-vinyl moiety of the substrate, 8-vinyl protochlorophyllide, producing protochlorophyllide a. A structural model for BciB based on a recent structure for the FrhB subunit of F420-reducing [NiFe]-hydrogenase of Methanothermobacter marburgensis is proposed. Possible reasons for the occurrence and distribution of BciA and BciB among various chlorophototrophs are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Various plants possess hydrophilic chlorophyll (Chl) proteins known as water-soluble Chl-binding proteins (WSCPs). WSCPs exist in two forms: Class I and Class II, of which Class I alone exhibits unique photoconvertibility. Although numerous genes encoding Class II WSCPs have been identified and the molecular properties of their recombinant proteins have been well characterized, no Class I WSCP gene has been identified to date. In this study, we cloned the cDNA and a gene encoding the Class I WSCP of Chenopodium album (CaWSCP). Sequence analyses revealed that CaWSCP comprises a single exon corresponding to 585bp of an open reading frame encoding 195 amino acid residues. The CaWSCP protein sequence possesses a signature of DUF538, a protein superfamily of unknown function found almost exclusively in Embryophyta. The recombinant CaWSCP was expressed in Escherichia coli as a hexa-histidine fusion protein (CaWSCP-His) that removes Chls from the thylakoid. Under visible light illumination, the reconstituted CaWSCP-His was successfully photoconverted into a different pigment with an absorption spectrum identical to that of native CaWSCP. Interestingly, while CaWSCP-His could bind both Chl a and Chl b, photoconversion occurred only in CaWSCP-His reconstituted with Chl a. [Copyright &y& Elsevier]

The dependence of excitation energytransfer kinetics on the electronic state of the acceptor (groundvs excited) has been resolved with a novel multipulse prePump–Pump–Probespectroscopy. The primary energy transfer and annihilation dynamicsin two model light-harvesting systems were explored: an artificiallysynthesized carotenoid-zinc-phthalocyanine dyad and a naturally occurringlight-harvesting peridinin-chlorophyll protein complex from Amphidinium carterae. Both systems use carotenoid as theprimary excitation energy donor with porphyrin chromophores as theacceptor molecules. The prePump–Pump–Probe transientsignals were analyzed with Monte Carlo modeling to explicitly addressthe underlying step-by-step kinetics involved in both excitation migrationand annihilation processes. Both energy transfer and annihilationdynamics were demonstrated to occur with approximately the same ratein both systems, regardless of the excitation status of the acceptorpigments. The possible reasons for these observations are discussedin the framework of the Förster energy transfer model. [ABSTRACT FROM AUTHOR]

The review summarizes the current understanding of light-inducible proteins of plants, wide-spread among prokaryotic and eukaryotic photosynthetic organisms. The greatest attention is paid to the Early light-inducible proteins of plastids (Elip) and their photoprotective role under light stress. Data are presented on structure and functions of Elip-related proteins such as Ohp/Hlip, Sep, and on the family of Cab proteins, chlorophyll a/ b-binding proteins of photosystems I and II, which are in many properties similar to Elip proteins. The multigene family of proteins of light-harvesting complexes (LHC) are discussed together with the possible ways of their evolution. [ABSTRACT FROM AUTHOR]

Highlights: [•] Chlorophyll a/b binding protein plays a key role in Ponkan fruit degreening. [•] CitCHLH regulates natural, but not ethylene induced, degreening. [•] CitChlase and CitNYC regulate ethylene induced, but not natural, degreening. [ABSTRACT FROM AUTHOR]

The fucoxanthin chlorophyll (Chl) a/c-binding protein (FCP) is responsiblefor excellent light-harvestingstrategies that enable survival in fluctuating light conditions. Here,we report the light-harvesting and quenching states of two FCP complexes,FCP-A and FCP-B/C, isolated from the diatom Chaetocerosgracilis. Pigment analysis revealed that FCP-A isenriched in Chl c, whereas FCP-B/C is enriched indiadinoxanthin, reflecting differences in low-temperature steady-stateabsorption and fluorescence spectra of each FCP complex. Time-resolvedfluorescence spectra were measured at 77 K, and the characteristiclifetimes were determined using global fitting analysis of the spectra.Tens of picosecond (ps) components revealed energy transfer to low-energyChl afrom Chls aand c, whereas the other components showed only fluorescence decay componentswith no concomitant rise components. The normalized amplitudes ofhundreds of picosecond components were relatively 30% in the totalfluorescence, whereas those of longest-lived components were 60%.The hundreds of picosecond components were assigned as excitationenergy quenching, whereas the longest-lived components were assignedas fluorescence from the final energy traps. These results suggestthat 30% of FCP complex forming quenching state and the other 60%of FCP complex forming light-harvesting state exist heterogeneouslyin each FCP fraction under continuous low-light condition. [ABSTRACT FROM AUTHOR]