Genome-wide identification and expression profiling of photosystem II(PsbX)gene family in upland cotton(Gossypium hirsutum L.)

Background Photosystem II(PSII)constitutes an intricate assembly of protein pigments,featuring extrinsic and intrinsic polypeptides within the photosynthetic membrane.The low-molecular-weight transmembrane protein PsbX has been identified in PSII,which is associated with the oxygen-evolving complex.The expression of PsbX gene protein is regulated by light.PsbX’s central role involves the regulation of PSII,facilitating the binding of quinone molecules to the Qb(PsbA)site,and it additionally plays a crucial role in optimizing the efficiency of photosynthesis.Despite these insights,a comprehensive understanding of the PsbX gene’s functions has remained elusive.Results In this study,we identified ten PsbX genes in Gossypium hirsutum L.The phylogenetic analysis results showed that 40 genes from nine species were classified into one clade.The resulting sequence logos exhibited substantial conservation across the N and C terminals at multiple sites among all Gossypium species.Furthermore,the ortholo-gous/paralogous,Ka/Ks ratio revealed that cotton PsbX genes subjected to positive as well as purifying selection pressure might lead to limited divergence,which resulted in the whole genome and segmental duplication.The expression patterns of GhPsbX genes exhibited variations across specific tissues,as indicated by the analysis.Moreover,the expression of GhPsbX genes could potentially be regulated in response to salt,intense light,and drought stresses.Therefore,GhPsbX genes may play a significant role in the modulation of photosynthesis under adverse abiotic conditions.Conclusion We examined the structure and function of PsbX gene family very first by using comparative genom-ics and systems biology approaches in cotton.It seems that PsbX gene family plays a vital role during the growth and development of cotton under stress conditions.Collectively,the results of this study provide basic information to unveil the molecular and physiological function of PsbX genes of cotton plants.

Photoinduced hydrogen evolution in an artificial system containing photosystem I, hydrogenase, methy1 viologen and mercaptoacetic acid

Hydrogen evolution was detected in an artificial system composed of light-harvesting unit of purified photosystem I, catalyst of hydrogenase, methyl viologen and electron donor under radiation. Absorption spectral features confirmed that electron transfer from electron donors to proton was via a photoinduced reductive process of methyl viologen.

Different Effects of Malate on the Activities of Photosystem II in Detached Leaves of Maize and Tobacco

Malate is the first stable product after CO2 is fixed in NADP-dependent malic enzyme (NADP-ME) type of C4 plants, which transfers CO2 and the reducing equivalent from mesophyll cell (MC) to vascular bundle sheath cell (BSC) chloroplasts and affects the redox state of BSC. The aim of this experiment is to investigate the effect of exogenous malate on the activity of photosystem II (PS II) in C4 and C3 plants. The leaf discs from the 5th fully expanded leaves of maize (NADP-ME type C4 plants) and the 10th fully expanded leaves of tobacco (C3 plants) were treated with malate of 50, 100 μM and the chlorophyll fluorescence parameters were measured. Malate treatments decreased the photochemical reaction efficiency (FV/FM) in maize leaves, as a result of rising in initial fluorescence (FO) and decreasing in maximal fluorescence (FM). The number of active PS II reaction center (RC) per excited cross section (RC/CS) declined in malate-treated maize, suggesting that malate inactivated PS II RC. Malate treatments also increased Wk, representing the severity of oxygen-evolving complex (OEC) damage, and decreased the rate of photosynthetic oxygen evolution. We conclude that exogenous malate regulates the activity and structure of PS II in C4 plant maize. No significant changes in the activity of PS II were observed in malate-treated C3 plant tobacco. It is suggested that the short term malate treatment will inhibit PS II of leaves which have C4 anatomy and C4 enzymes.

Optimum Dark Adaptation Period for Evaluating the Maximum Quantum Efficiency of Photosystem II in Ozone-Exposed Rice Leaves

Because the transient O3 injury of leaves is lost with time, the evaluation of O3 effect on the maximum quantum efficiency of PSII (Fv/Fm) is difficult. Thus, the authors examined Fv/Fm in rice leaves exposed to different O3 concentrations (0, 0.1, and 0.3 cm3·m-3, expressed as O0, O0.1, and O0.3) under different dark adaptation periods (0, 1, 5, 10, 20, and 30 min, expressed as D0, D1, D5, D10, D20, and D30) to ascertain its optimum time span. Fv/Fm was inhibited by O3;however in the O0 and O0.1 plants, it recovered during dark adaptation. In the O0.3 plants, Fv/Fm decreased gradually with time. F0 was found to be increased by O3, and it increased further in the O0.3 plants during dark adaptation. Under a high light intensity, Fm was decreased by O3, and the O3-induced damage to Fv/Fm was therefore more pronounced. However, the sensitivity of

Effects of drought treatment on photosystemⅡactivity in the ephemeral plant Erodium oxyrhinchum

Drought is a critical limiting factor affecting the growth and development of plants in arid and semi-arid areas.Photosynthesis,one of the most important physiological processes of plants,can be significantly inhibited by drought.PhotosystemⅡ(PSⅡ)is considered the main attack target when photosynthesis is affected by drought.To clarify how PSⅡcomponents of the ephemeral plant Erodium oxyrhinchum(grown in the Gurbantunggut Desert,China)respond to drought treatment,we evaluated the functional activity of PSII by determining chlorophyll fluorescence and gas exchange parameters under different drought treatment levels(control(400 mL),moderate drought(200 mL),and severe drought(100 m L)).Under moderate drought treatment,significant decreases were found in net photosynthetic rate(Pn),effective quantum yield of PSII(Y(Ⅱ)),relative electron transfer rate of PSII(rETR(Ⅱ)),oxygen-releasing complex,probability of an absorbed exciton moving an electron into the electron transport chain beyond primary quinone receptor Q_(A)-(Φ(E_(o))),probability of a trapped exciton moving an electron into the electron transport chain beyond primary quinone receptor Q_(A)-(ψ(E_(o))),and performance index of PSⅡ(PI_(abs)).Compared to control treatment,marked increases were observed in water use efficiency(WUE),relative variable fluorescence at the J step(V_(J)),initial fluorescence(F_(o)),and dissipated energy per active reaction center(DI_(o)/RC)under moderate drought treatment,but there were no substantial changes in semi-saturated light intensity(I_(K)),active reaction centers per cross-section(RC/CS),and total performance index of PSII and PSI(PI_(total),where PSI is the photosystemⅠ).The changes of the above parameters under severe drought treatment were more significant than those under moderate drought treatment.In addition,severe drought treatment significantly increased the absorbed energy per active reaction center(ABS/RC)and trapping energy per active reaction center(TR_(o)/RC)but decreased the energy transmission connectivity of PSⅡcomponents,RC/CS,and PI_(total),compared to moderate drought and control treatments.Principle component analysis(PCA)revealed similar information according to the grouping of parameters.Moderate drought treatment was obviously characterized by RC/CS parameter,and the values of F_(o),V_(J),ABS/RC,DI_(o)/RC,and TR_(o)/RC showed specific reactions to severe drought treatment.These results demonstrated that moderate drought treatment reduced the photochemical activity of PSII to a certain extent but E.oxyrhinchum still showed strong adaptation against drought treatment,while severe drought treatment seriously damaged the structure of PSⅡ.The results of this study are useful for further understanding the adaptations of ephemeral plants to different water conditions and can provide a reference for the selection of relevant parameters for photosynthesis measurements of large samples in the field.

Effect of high light and desiccation on photosystem Ⅱ in the seedlings and mature plants of tropical seagrass Enhalus acoroides during low tide

During low tide,the intertidal seagrass Enhalus acoroides is often exposed to high light and desiccation,which can seriously threaten its survival,at least partly by inhibiting photosystem Ⅱ(PSⅡ)activity.The response of leaves of E.acoroides to high light and desiccation was compared for seedlings and mature plants.Results show that the resistance of seedling and mature leaves to high light was quite similar,but to desiccation was very different.Seedling leaves were more sensitive to desiccation than the mature plant leaves,but had better water retention.The damage of desiccation to seedling leaves was mainly caused by dehydration,whereas that to mature plant leaves was caused by hypersaline toxicity.The recovery rate of PSⅡ of seedling leaves was significantly slower than that of the mature plants after the stresses disappeared,which may at least partly contribute to seedling mortality in the wild.In addition,compared to high light,desiccation seriously inhibited the recovery rate of PSⅡ activities even if the leaves became fully rehydrated to their normal relative water content(RWC)in the following re-immersion.Desiccation inhibited the recovery rate of RC/CS_(M)(reaction center per cross section(at t=t_(Fm)))to decrease the production of assimilatory power,which maybe the cause of the slower PSⅡ recovery in desiccation treatments.This study demonstrates that desiccation particularly coupling with high light have a very negative ef fect on the PSⅡ of E.acoroides during low tide and the sensitivity of seedlings and mature plants to desiccation is significantly different,which have important reference significance to choose an appropriate transplanting depth where seedlings and mature plants of E.acoroides not only receive sufficient light for growth,but also that minimize desiccation stress during low tide.

Blue light is more essential than red light for maintaining the activities of photosystem Ⅱ and Ⅰ and photosynthetic electron transport capacity in cucumber leaves

Blue and red lights differently regulate leaf photosynthesis. Previous studies indicated that plants under blue light generally exhibit better photosynthetic characteristics than those under red light. However, the regulation mechanism of related photosynthesis characteristics remains largely unclear. Here, four light qualities treatments （300 μmol m-2 s-1） including white fluorescent light （FL）, blue monochromatic light （B, 440 nm）, red monochromatic light （R, 660 nm）, and a combination of red and blue light （RB, R：B=8：1） were carried out to investigate their effects on the activity of photosystem II （PSII） and photosystem I （PSI）, and photosynthetic electron transport capacity in the leaves of cucumber （Cucumis sativus L.） seedlings. The results showed that compared to the FL treatment, the R treatment significantly limited electron transport rate in PSII （ETR11） and in PSI （ETR1） by 79.4 and 66.3%, respectively, increased non-light induced non-photochemical quenching in PSII （q^No） and limitation of donor side in PSI （φND） and reduced most JIP-test parameters, suggesting that the R treatment induced suboptimal activity of photosystems and inhibited electron transport from PSII donor side up to PSI. However, these suppressions were effectively alleviated by blue light addition （RB）. Compared with the R treatment, the RB treatment significantly increased ETR, and ETR1 by 176.9 and 127.0%, respectively, promoted photosystems activity and enhanced linear electron transport by elevating electron transport from QA to PSI. The B treatment plants exhibited normal photosystems activity and photosynthetic electron transport capacity similar to that of the FL treatment. It was concluded that blue light is more essential than red light for normal photosynthesis by mediating photosystems activity and photosynthetic electron transport capacity.

Calcium contributes to photoprotection and repair of photosystem II in peanut leaves during heat and high irradiance

In this study, we investigated the effects of exogenous calcium nitrate on photoinhibition and thylakoid protein level in peanut plants under heat （40 ℃） and high irradiance （HI） （1,200 mmol/m2 per s） stress. Compared with control seedlings （cultivated in 0 mmol/L Ca（NO3）2 medium）, the maximal photochemical efficiency of photosystem II （PSII） in Ca2t‐treated plants showed a slight decrease after 5 h stress, accompanied by lower degree of PSII closure （1‐qP）, higher non‐photochemical quenching, and lower level of membrane damage. Ca2t inhibitors were used to analyze the varieties of antioxidant enzymes activity and PSII proteins. These results indicated that Ca2t could protect the subunits of PSII reaction centers from photoinhibition by reducing the generation of reactive oxygen species. In the presence of both ethyleneglycol‐bis（2‐aminoethylether）‐tetraacetic acid and ascorbic acid （AsA）, the net degradation of the damaged D1 protein was faster than that only treated with AsA. Our previous study showed that either the transcriptional or the translational level of calmodulin was obviously higher in Ca2t‐treated plants. These results suggested that, under＆amp;nbsp;heat and HI stress, the Ca2t signal transduction pathway can al eviate the photoinhibition through regulating the protein repair process besides an enhanced capacity for scavenging reactive oxygen species.

Roles of manganese in photosystem II dynamics to irradiations and temperatures

The most amazing chemistry is the light-driven water splitting reaction occurred in the oxygen-evolving complex of phototsystem II in higher plants, green algae, and cyanobacteria. Mn, in the form of Mn4CaOs cluster in photosystem II, is responsible for the catalytic water splitting reaction as well as plays roles in photosystem II dynamics to irradiation and temperatures. Manganese hypothesis of UV-initiated photoinhibition as a direct target is established, and thermal inactivation of photosystem II involves the valence and structural changes of manganese. Recent progresses in understanding the roles of manganese in photoinhibition especially under UV light and in thermal inactivation including elevated temperatures using synthetic models and native PS II complexes are summarized and evaluated. Potential problems and possible solutions are discussed and presented.

Oxygen-evolving Activity in Photosystem II Core Complex of Photosynthetic Membrane in the Presence of Native Lipid

The techniques of oxygen electrode polarography and Fourier transform infrared (FT IR) spectroscopy were employed to explore the involvement of digalactosyl diacylglycerol (DGDG) in functional and structural roles in the photosystem II core complex (PSIICC). It was shown that DGDG exhibited the ability to stimulate the oxygen evolution in PSIICC, which was accompanied by the changes in the structures of PSIICC proteins. The results revealed that there existed hydrogen bonding interactions between DGDG molecules and PSIICC proteins. It is most likely that the sites of PSIICC interaction with DGDG are in the extrinsic protein of 33 kDa.

Assembly of CdTe Quantum Dots and Photosystem II Multi- layer Films with Enhanced Photocurrent

Photosystem II （PSII） is a photoactive protein that can drive water oxidation under light irradiation. Recently, PSII has been broadly investigated with the high demand on the bioenergy. Here, we demonstrate a facile approach for the fabrication of a photoactive electrode by the integration of PSII with quantum dots （QDs）/polyelectrolyte multilayers. The assembled QDs and PSII film with a polyelectrolyte based substrate via layer-by-layer assembly can remain the photoactivity of the PSII and broaden the absorption spectrum of PSII to produce a high photocur- rent yield. The co-assembly exhibits an obviously enhanced photocurrent under UV light irradiation. The proposed strategy can be considered for the reference and usage of PSII toward the solar energy conversion.

Structure of plant photosystem I−light harvesting complex I supercomplex at 2.4Å resolution

Photosystem I(PSI)is one of the two photosystems in photosynthesis,and performs a series of electron transfer reactions leading to the reduction of ferredoxin.In higher plants,PSI is surrounded by four light-harvesting complex I(LHCI)subunits,which harvest and transfer energy efficiently to the PSI core.The crystal structure of PSI-LHCI supercomplex has been analyzed up to 2.6Åresolution,providing much information on the arrangement of proteins and cofactors in this complicated supercomplex.Here we have optimized crystallization conditions,and analyzed the crystal structure of PSI-LHCI at 2.4Åresolution.Our structure showed some shift of the LHCI,especially the Lhca4 subunit,away from the PSI core,suggesting the indirect connection and inefficiency of energy transfer from this Lhca subunit to the PSI core.We identified five new lipids in the structure,most of them are located in the gap region between the Lhca subunits and the PSI core.These lipid molecules may play important roles in binding of the Lhca subunits to the core,as well as in the assembly of the supercomplex.The present results thus provide novel information for the elucidation of the mechanisms for the light-energy harvesting,transfer and assembly of this supercomplex.

A unique photosystem I reaction center from a chlorophyll d-containing cyanobacterium Acaryochloris marina

Photosystem I(PSI)is a large protein supercomplex that catalyzes the light-dependent oxidation of plastocyanin(or cytochrome c6)and the reduction of ferredoxin.This catalytic reaction is realized by a transmembrane electron transfer chain consisting of primary electron donor(a special chlorophyll(Chl)pair)and electron acceptors A_(0),A_(1),and three Fe_(4)S_(4) clusters,F_(X),F_(A),and F_(B).Here we report the PSI structure from a Chl d-dominated cyanobacterium Acaryochloris marina at 3.3Åresolution obtained by single-particle cryo-electron microscopy.The A.marina PSI exists as a trimer with three identical monomers.Surprisingly,the structure reveals a unique composition of electron transfer chain in which the primary electron acceptor A_(0) is composed of two pheophytin a rather than Chl a found in any other well-known PSI structures.A novel subunit Psa27 is observed in the A.marina PSI structure.In addition,77 Chls,13α-carotenes,two phylloquinones,three Fe-S clusters,two phosphatidyl glycerols,and one monogalactosyl-diglyceride were identified in each PSI monomer.Our results provide a structural basis for deciphering the mechanism of photosynthesis in a PSI complex with Chl d as the dominating pigments and absorbing far-red light.

Reduced salinity interacts with ultraviolet radiation to alter photosystem Ⅱ function in diatom Skeletonema costatum

To investigate the effect of reduced salinity on diatoms’ capacity to cope with changing ultraviolet radiation(U VR) and photosynthetically active radiation(PAR),Skeletonema costatum was grown in a range of salinity(15,25,and 35).The photo system Ⅱ(PSⅡ) function was analyzed by increasing PAR and UVR to mimic a mixing event in turbulent waters.The re sults show that high UVR exposure significantly reduced PSII activity,especially in cells grown at low salinity.UVR,but not salinity,stimulated the ’removal’ rate of PSII protein PsbA.Salinity alone,in the range of 15 to 35,did not regulate PSⅡ acceptor region;however,the low salinity+UVR treatment decreased the energy flux for electron transport per PSⅡ reaction center in S.costatum.It showed that low salinity exacerbated the damaging effect of UVR on PSⅡ function in S.costatum by suppressing Psb A protein synthe sis and modifying the photochemistry of PSⅡ.Although higher catalase(CAT) activity and NPQs were induced,they were unable to prevent the combined damage effect of low salinity+UVR.Our findings indicate that reduced salinity and increased UVR potentially affect the abundance and distribution of S.costatum with the escalation of climate disturbances.

Bidirectional Electron Transfer in the Reaction Centre of Photosystem I

In the past decade light-induced electron transfer reactions in photosystem I have been the subject of intensive investigations that have led to the elucidation of some unique characteristics, the most striking of which is the existence of two parallel, functional, redox active cofactors chains. This process is generally referred to as bidirectional electron transfer. Here we present a review of the principal evidences that have led to the uncovering of bidirectionality in the reaction centre of photosystem I. A special focus is dedicated to the results obtained combining time-resolved spectroscopic techniques, either difference absorption or electron paramagnetic resonance, with molecular genetics, which allows, through modification of the binding of redox active cofactors with the reaction centre subunits, an effect on their physical-chemical properties.

Elucidating the Molecular Mechanism of Dynamic Photodamage of Photosystem II Membrane Protein Complex by Integrated Proteomics Strategy

Photosystem II(PSII),as a multiple-subunit chloroplast membrane-associated pigment-protein complex on the thylakoid membrane,is a primary target of light-induced photodamage.However,the overall molecular details of the conformation and composition dynamics of PSII photodamage are still controversial.In this study,we investigated systematically the dynamic conformation,degradation,and oxidation processes of PSII photodamage by integrating chemical cross-linking and top-down proteomics strategies.

Exogenous SA or 6-BA maintains photosynthetic activity in maize leaves under high temperature stress

With global warming, high-temperature(HT) stress has become a major abiotic stress for crops, in particular summer maize in China. Photosynthesis is sensitive to HT. Salicylic acid(SA) and 6-benzyladenine(6-BA) can improve the adaptation of plants to various biotic and abiotic stresses. However, their contribution to maintaining photosynthetic activity and alleviating photoinhibition in maize leaves under HT stress is still unclear. The effects of exogenous SA or 6-BA on growth, photosynthesis capacity, photosystem Ⅱ(PSII) activity, subcellular ultrastructure, antioxidant system, and plant hormones in maize leaves under HT stress were investigated. Under HT conditions, application of SA or 6-BA up-regulated gibberellin and zeatin content in leaves, increasing leaf area index(LAI). It also expanded the stomata by reducing abscisic acid and jasmonic acid content in leaves, cooling them and increasing CO2supply to photosynthesis. A higher net photosynthetic rate, combined with increased activity of the antioxidant system, alleviated oxidative stress in maize plants sprayed with SA or 6-BA, allowing them to maintain their chloroplast ultrastructure and PSII activity, in particular electron transfer from QAto QB. The increased LAI and net photosynthetic rate per unit leaf area also resulted in the accumulation of more biomass.

Cryo-EM structure of a tetrameric photosystem I from Chroococcidiopsis TS-821, a thermophilic, unicellular, non-heterocyst-forming cyanobacterium

Photosystem I(PSI)is one of two photosystems involved in oxygenic photosynthesis.PSI of cyanobacteria exists in monomeric,trimeric,and tetrameric forms,in contrast to the strictly monomeric form of PSI in plants and algae.The tetrameric organization raises questions about its structural,physiological,and evolutionary significance.Here we report the3.72 A˚resolution cryo-electron microscopy structure of tetrameric PSI from the thermophilic,unicellular cyanobacterium Chroococcidiopsis sp.TS-821.The structure resolves 44 subunits and 448 cofactor molecules.We conclude that the tetramer is arranged via two different interfaces resulting from a dimer-of-dimers organization.The localization of chlorophyll molecules permits an excitation energy pathway within and between adjacent monomers.Bioinformatics analysis reveals conserved regions in the PsaL subunit that correlate with the oligomeric state.Tetrameric PSI may function as a key evolutionary step between the trimeric and monomeric forms of PSI organization in photosynthetic organisms.

Release of the Oxygen-Evolving Complex Subunits from Photosystem II Membranes in Phosphorylation Condition under Light Stress

So far it is unclear whether the release of oxygen-evolving complex （OEC） subunits including PsbO, PsbP, and PsbQ proteins is affected by the phosphorylation of photosystem II （PSII） membranes under light stress. In this work, different phosphorylated PSII membranes were obtained from spinach. Phosphorylation partially suppressed the release of PsbO, PsbP, and PsbQ proteins from PSII membranes under light stress. Reactive oxygen species including superoxide anion, hydrogen peroxide and hydroxyl radical, were involved in the release of a small part of PsbO protein, but not in the release of PsbP and PsbQ proteins in the non-phosphorylated and phosphorylated PSII membranes. All of the results suggested that the release of PsbO, PsbP, and PsbQ proteins was partially regulated by phosphorylation in PSII membranes, and the role of reactive oxygen species in the release of OEC subunits in non-phosphorylated PSII membranes was the same as in phosphorylated PSII membranes.

Assembly mechanism and energy transfer pathways of plant photosystem II-LHCII supercomplexes discovered through cryo-electron microscopy

Funded by the National Natural Science Foundation of China,Chinese Ministry of Science and Technology,and Chinese Academy of Sciences,ajoint team of three laboratories from the Institute of Biophysics of Chinese Academy of Sciences,namely Liu Zhenfeng’s(柳振峰),Zhang