The PsbY protein of Arabidopsis Photosystem II is important for the redox control of cytochrome b559

RESISTANCE TO PHYTOPHTHORA1 promotes cytochrome b559 formation during early photosystem II biogenesis in Arabidopsis

As an essential intrinsic component of photosystem II (PSII) in all oxygenic photosynthetic organisms, heme-bridged heterodimer cytochrome b559 (Cyt b559) plays critical roles in the protection and assembly of PSII. However, the underlying mechanisms of Cyt b559 assembly are largely unclear. Here, we characterized the Arabidopsis (Arabidopsis thaliana) rph1 (resistance to Phytophthora1) mutant, which was previously shown to be susceptible to the oomycete pathogen Phytophthora brassicae. Loss of RPH1 leads to a drastic reduction in PSII accumulation, which can be primarily attributed to the defective formation of Cyt b559. Spectroscopic analyses showed that the heme level in PSII supercomplexes isolated from rph1 is significantly reduced, suggesting that RPH1 facilitates proper heme assembly in Cyt b559. Due to the loss of RPH1-mediated processes, a covalently bound PsbE-PsbF heterodimer is formed during the biogenesis of PSII. In addition, rph1 is highly photosensitive and accumulates elevated levels of reactive oxygen species under photoinhibitory-light conditions. RPH1 is a conserved intrinsic thylakoid protein present in green algae and terrestrial plants, but absent in Synechocystis, and it directly interacts with the subunits of Cyt b559. Thus, our data demonstrate that RPH1 represents a chloroplast acquisition specifically promoting the efficient assembly of Cyt b559, probably by mediating proper heme insertion into the apo-Cyt b559 during the initial phase of PSII biogenesis.

Physiological and transcriptome level responses of Microcystis aeruginosa and M. viridis to environmental concentrations of triclosan

The toxicity of triclosan (TCS) to various aquatic organisms has been demonstrated at environmental concentrations. However, the effects and mechanisms of TCS on toxic cyanobacteria remains largely unexplored. This study investigated the physiological and molecular variations in two representative toxic Microcystis species (M. aeruginosa and M. viridis) under exposure to TCS for 12 d. Our findings demonstrated that the median effective concentration (EC50) of TCS for both Microcystis species were close to the levels detected in the environment (M. aeruginosa: 9.62 μg L-1; M. viridis: 27.56 μg L-1). An increased level of reactive oxygen species (ROS) was observed in Microcystis, resulting in oxidative damage when exposed to TCS at concentrations ranging from 10 μg L-1 to 50 μg L-1. The photosynthetic activity of Microcystis had a certain degree of recovery capability at low concentrations of TCS. Compared to M. aeruginosa, the higher recovery capability of the photosynthetic system in M. viridis would be mainly attributed to the increased ability for PSII repair and phycobilisome synthesis. Additionally, the synthesis of microcystins in the two species and the release rate in M. viridis significantly increased under 10-50 μg L-1 TCS. At the molecular level, exposure to TCS at EC50 for 12 d induced the dysregulation of genes associated with photosynthesis and antioxidant system. The upregulation of genes associated with microcystin synthesis and nitrogen metabolism further increased the potential risk of microcystin release. Our results revealed the aquatic toxicity and secondary ecological risks of TCS at environmental concentrations, and provided theoretical data with practical reference value for TCS monitoring.

Deciphering the Enhancing Impact of Exogenous Brassinolide on Physiological Indices of Melon Plants under Downy Mildew-Induced Stress

Melon (Cucumis melo L.) is a valuable horticultural crop of the Cucurbitaceae family. Downy mildew (DM), caused by Pseudoperonospora cubensis, is a significant inhibitor of the production and quality of melon. Brassinolide (BR) is a new type of phytohormone widely used in cultivation for its broad spectrum of resistance- and defense-mechanism-improving activity. In this study, we applied various exogenous treatments (0.5, 1.0, and 2.0 mg·L-1) of BR at four distinct time periods (6 h, 12 h, 24 h, and 48 h) and explored the impact of BR on physiological indices and the genetic regulation of melon seedling leaves infected by downy-mildew-induced stress. It was mainly observed that a 2.0 mg·L-1 BR concentration effectively promoted the enhanced photosynthetic activity of seedling leaves, and quantitative real-time polymerase chain reaction (qRT-PCR) analysis similarly exhibited an upregulated expression of the predicted regulatory genes of photosystem II (PSII) CmHCF136 (MELO3C023596.2) and CmPsbY (MELO3C010708.2), thus indicating the stability of the PSII reaction center. Furthermore, 2.0 mg·L-1 BR resulted in more photosynthetic pigments (nearly three times more than the chlorophyll contents (264.52%)) as compared to the control and other treatment groups and similarly upregulated the expression trend of the predicted key enzyme genes CmLHCP (MELO3C004214.2) and CmCHLP (MELO3C017176.2) involved in chlorophyll biosynthesis. Meanwhile, the maximum contents of soluble sugars and starch (186.95% and 164.28%) were also maintained, which were similarly triggered by the upregulated expression of the predicted genes CmGlgC (MELO3C006552.2), CmSPS (MELO3C020357.2), and CmPEPC (MELO3C018724.2), thereby maintaining osmotic adjustment and efficiency in eliminating reactive oxygen species. Overall, the exogenous 2.0 mg·L-1 BR exhibited maintained antioxidant activities, plastid membranal stability, and malondialdehyde (MDA) content. The chlorophyll fluorescence parameter values of F0 (42.23%) and Fv/Fm (36.67%) were also noticed to be higher; however, nearly three times higher levels of NPQ (375.86%) and Y (NPQ) (287.10%) were observed at 48 h of treatment as compared to all other group treatments. Increased Rubisco activity was also observed (62.89%), which suggested a significant role for elevated carbon fixation and assimilation and the upregulated expression of regulatory genes linked with Rubisco activity and the PSII reaction process. In short, we deduced that the 2.0 mg·L-1 BR application has an enhancing effect on the genetic modulation of physiological indices of melon plants against downy mildew disease stress.

Physiological responses and transcriptome analysis of soybean under gradual water deficit

Soybean is an important food and oil crop widely cultivated globally. However, water deficit can seriously affect the yield and quality of soybeans. In order to ensure the stability and increase of soybean yield and improve agricultural water use efficiency (WUE), research on improving drought tolerance and the efficiency of water utilization of soybeans under drought stress has become particularly important. This study utilized the drought-tolerant variety Heinong 44 (HN44) and the drought-sensitive variety Suinong 14 (SN14) to analyze physiological responses and transcriptome changes during the gradual water deficit at the early seed-filling stage. The results indicated that under drought conditions, HN44 had smaller stomata, higher stomatal density, and lower stomatal conductance (Gs) and transpiration rate as compared to SN14. Additionally, HN44 had a higher abscisic acid (ABA) content and faster changes in stomatal morphology and Gs to maintain a dynamic balance between net photosynthetic rate (Pn) and Gs. Additionally, drought-tolerant variety HN44 had high instantaneous WUE under water deficit. Further, HN44 retained a high level of superoxide dismutase (SOD) activity and proline content, mitigating malondialdehyde (MDA) accumulation and drought-induced damage. Comprehensive analysis of transcriptome data revealed that HN44 had fewer differentially expressed genes (DEGs) under light drought stress, reacting insensitivity to water deficit. At the initial stage of drought stress, both varieties had a large number of upregulated DEGs to cope with the drought stress. Under severe drought stress, HN44 had fewer downregulated genes enriched in the photosynthesis pathway than SN14, while it had more upregulated genes enriched in the ABA-mediated signaling and glutathione metabolism pathways than SN14. During gradual water deficit, HN44 demonstrated better drought-tolerant physiological characteristics and water use efficiency than SN14 through key DEGs such as GmbZIP4, LOC100810474, and LOC100819313 in the major pathways. Key transcription factors were screened and identified, providing further clarity on the molecular regulatory pathways responsible for the physiological differences in drought tolerance among these varieties. This study deepened the understanding of the drought resistance mechanisms in soybeans, providing valuable references for drought-resistant soybean breeding.

Transcriptome Analysis Reveals the Response Mechanism of Digitaria sanguinalis, Arabidopsis thaliana and Poa annua under 4,8-Dihydroxy-1-tetralone Treatment

4,8-dihydroxy-l-tetralone (4,8-DHT) is an allelochemical isolated from the outer bark of Carya cathayensis that acts as a plant growth inhibitor. In order to explore the mechanism of 4,8-DHT inhibiting weed activity, we treated three species of Digitaria sanguinalis, Arabidopsis thaliana, and Poa annua with different concentrations of 4,8-DHT and performed phenotype observation and transcriptome sequencing. The results showed that with an increase in 4,8-DHT concentration, the degree of plant damage gradually deepened. Under the same concentration of 4,8-DHT, the damage degree of leaves and roots of Digitaria sanguinalis was the greatest, followed by Arabidopsis thaliana, while Poa annua had the least damage, and the leaves turned slightly yellow. Transcriptome data showed that 24536, 9913, and 1662 differentially expressed genes (DEGs) were identified in Digitaria sanguinalis, Arabidopsis thaliana, and Poa annua, respectively. These DEGs were significantly enriched in photosynthesis, carbon fixation, glutathione metabolism, phenylpropanoid biosynthesis, and oxidative phosphorylation pathways. In addition, DEGs were also enriched in plant hormone signal transduction and the MAPK signal pathway in Arabidopsis thaliana. Further analysis showed that after 4,8-DHT treatment, the transcript levels of photosynthesis PSI- and PSII-related genes, LHCA/B-related genes, Rubisco, and PEPC were significantly decreased in Digitaria sanguinalis and Arabidopsis thaliana. At the same time, the transcription levels of genes related to glutathione metabolism and the phenylpropanoid biosynthesis pathway in Digitaria sanguinalis were also significantly decreased. However, the expression of these genes was upregulated in Arabidopsis thaliana and Poa annua. These indicated that 4,8-DHT affected the growth of the three plants through different physiological pathways, and then played a role in inhibiting plant growth. Simultaneously, the extent to which plants were affected depended on the tested plants and the content of 4,8-DHT. The identification of weed genes that respond to 4,8-DHT has helped us to further understand the inhibition of plant growth by allelochemicals and has provided a scientific basis for the development of allelochemicals as herbicides.

Integrated agronomic, physiological, microstructure, and whole-transcriptome analyses reveal the role of biomass accumulation and quality formation during Se biofortification in alfalfa

Se-biofortified agricultural products receive considerable interest due to the worldwide severity of selenium (Se) deficiency. Alfalfa (Medicago sativa L.), the king of forage, has a large biomass, a high protein content, and a high level of adaptability, making it a good resource for Se biofortification. Analyses of agronomic, quality, physiological, and microstructure results indicated the mechanism of biomass increase and quality development in alfalfa during Se treatment. Se treatment effectively increased Se content, biomass accumulation, and protein levels in alfalfa. The enhancement of antioxidant capacity contributes to the maintenance of low levels of reactive oxygen species (ROS), which, in turn, serves to increase alfalfa's stress resistance and the stability of its intracellular environment. An increase in the rate of photosynthesis contributes to the accumulation of biomass in alfalfa. To conduct a more comprehensive investigation of the regulatory networks induced by Se treatment, the transcriptome sequencing of non-coding RNA (ncRNA) was employed to compare 100 mg/kg Se treatment and control groups. The analysis identified 1,414, 62, and 5 genes as DE-long non-coding RNAs (DE-lncRNA), DE-microRNAs (DE-miRNA), and DE-circular RNA (DE-circRNA), respectively. The function of miRNA-related regulatory networks during Se biofortification in alfalfa was investigated. Subsequent enrichment analysis revealed significant involvement of transcription factors, DNA replication and repair mechanisms, photosynthesis, carbohydrate metabolism, and protein processing. The antioxidant capacity and protein accumulation of alfalfa were regulated by the modulation of signal transduction, the glyoxalase pathway, proteostasis, and circRNA/lncRNA-related regulatory networks. The findings offer new perspectives on the regulatory mechanisms of Se in plant growth, biomass accumulation, and stress responses, and propose potential strategies for enhancing its utilization in the agricultural sector.

Low nitrogen stress-induced transcriptome changes revealed the molecular response and tolerance characteristics in maintaining the C/N balance of sugar beet (Beta vulgaris L.)

Nitrogen (N) is an essential macronutrient for plants, acting as a common limiting factor for crop yield. The application of nitrogen fertilizer is related to the sustainable development of both crops and the environment. To further explore the molecular response of sugar beet under low nitrogen (LN) supply, transcriptome analysis was performed on the LN-tolerant germplasm '780016B/12 superior'. In total, 580 differentially expressed genes (DEGs) were identified in leaves, and 1,075 DEGs were identified in roots (log₂ ^|FC| ≥ 1; q value < 0.05). Gene Ontology (GO), protein-protein interaction (PPI), and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses clarified the role and relationship of DEGs under LN stress. Most of the downregulated DEGs were closely related to "photosynthesis" and the metabolism of "photosynthesis-antenna proteins", "carbon", "nitrogen", and "glutathione", while the upregulated DEGs were involved in flavonoid and phenylalanine biosynthesis. For example, GLUDB (glutamate dehydrogenase B) was identified as a key downregulated gene, linking carbon, nitrogen, and glutamate metabolism. Thus, low nitrogen-tolerant sugar beet reduced energy expenditure mainly by reducing the synthesis of energy-consuming amino acids, which in turn improved tolerance to low nitrogen stress. The glutathione metabolism biosynthesis pathway was promoted to quench reactive oxygen species (ROS) and protect cells from oxidative damage. The expression levels of nitrogen assimilation and amino acid transport genes, such as NRT2.5 (high-affinity nitrate transporter), NR (nitrate reductase [NADH]), NIR (ferredoxin-nitrite reductase), GS (glutamine synthetase leaf isozyme), GLUDB, GST (glutathione transferase) and GGT3 (glutathione hydrolase 3) at low nitrogen levels play a decisive role in nitrogen utilization and may affect the conversion of the carbon skeleton. DFRA (dihydroflavonol 4-reductase) in roots was negatively correlated with NIR in leaves (coefficient = -0.98, p < 0.05), suggesting that there may be corresponding remote regulation between "flavonoid biosynthesis" and "nitrogen metabolism" in roots and leaves. FBP (fructose 1,6-bisphosphatase) and PGK (phosphoglycerate kinase) were significantly positively correlated (p < 0.001) with Ci (intercellular CO₂ concentration). The reliability and reproducibility of the RNA-seq data were further confirmed by real-time fluorescence quantitative PCR (qRT-PCR) validation of 22 genes (R² = 0.98). This study reveals possible pivotal genes and metabolic pathways for sugar beet adaptation to nitrogen-deficient environments.

Photosynthetic modulation during the diurnal cycle in a unicellular diazotrophic cyanobacterium grown under nitrogen-replete and nitrogen-fixing conditions

Cyanobacteria are the only oxygenic photosynthetic organisms that can fix nitrogen. In diazotrophic cyanobacteria, the regulation of photosynthesis during the diurnal cycle is hypothesized to be linked with nitrogen fixation and involve the D1 protein isoform PsbA4. The amount of bioavailable nitrogen has a major impact on productivity in aqueous environments. In contrast to low- or nitrogen-fixing (-N) conditions, little data on photosynthetic regulation under nitrogen-replete (+ N) conditions are available. We compared the regulation of photosynthesis under -N and + N conditions during the diurnal cycle in wild type and a psbA4 deletion strain of the unicellular diazotrophic cyanobacterium Cyanothece sp. ATCC 51142. We observed common changes to light harvesting and photosynthetic electron transport during the dark in + N and -N conditions and found that these modifications occur in both diazotrophic and non-diazotrophic cyanobacteria. Nitrogen availability increased PSII titer when cells transitioned from dark to light and promoted growth. Under -N conditions, deletion of PsbA4 modified charge recombination in dark and regulation of PSII titer during dark to light transition. We conclude that darkness impacts the acceptor-side modifications to PSII and photosynthetic electron transport in cyanobacteria independently of the nitrogen-fixing status and the presence of PsbA4.

Exogenous uniconazole enhances tolerance to chilling stress in mung beans (Vigna radiata L.) through cross talk among photosynthesis, antioxidant system, sucrose metabolism, and hormones

To monitor the role of exogenous uniconazole in mitigating chilling stress, this study investigated the effect of foliar spraying of 50 mg L^-1 uniconazole on the chilling (15 °C) tolerance of mung beans at the flowering stage. The results showed that uniconazole significantly enhanced the reactive oxygen species (ROS) scavenging ability of mung beans by increasing the superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR) activities, the contents of ascorbic acid (AsA) and glutathione (GSH), and the transcription levels of SOD and POD under chilling stress. The uniconazole applications also drastically increased the net photosynthetic rate (P_n), maximum net photosynthetic rate (P_nmax), maximum quantum yield of PSII (F_v/F_m), and the expression levels of the corresponding photosynthetic genes PsbO, PsbP, PsbQ, PsbY, and Psb28. This, in turn, resulted in a higher sucrose content. Meanwhile, uniconazole increased the indole-3-acetic acid (IAA) content but reduced the gibberellin A3 (GA₃) content under chilling stress. During the recovery period, the photosynthetic parameters and ROS of plants receiving uniconazole recovered faster, and the antioxidant activity and non-antioxidant contents were higher than in chilling-treated plants. Additionally, chilling stress markedly reduced the pod number per plant, grain number per plant, and 100-seed weight, whereas uniconazole significantly increased the grain weight per plant by 53.47% compared to the chilling treatment. These results strongly suggest that uniconazole can effectively protect mung beans from chilling stress damage by protecting the photosynthetic machinery and enhancing the antioxidant capacity to quench excessive ROS caused by chilling stress. These effects are closely relevant to chilling tolerance enhancement and yield improvement in mung beans.

New Structural and Mechanistic Insights Into Functional Roles of Cytochrome b 559 in Photosystem II

Cytochrome (Cyt) b ₅₅₉ is a key component of the photosystem II (PSII) complex for its assembly and proper function. Previous studies have suggested that Cytb ₅₅₉ has functional roles in early assembly of PSII and in secondary electron transfer pathways that protect PSII against photoinhibition. In addition, the Cytb ₅₅₉ in various PSII preparations exhibited multiple different redox potential forms. However, the precise functional roles of Cytb ₅₅₉ in PSII remain unclear. Recent site-directed mutagenesis studies combined with functional genomics and biochemical analysis, as well as high-resolution x-ray crystallography and cryo-electron microscopy studies on native, inactive, and assembly intermediates of PSII have provided important new structural and mechanistic insights into the functional roles of Cytb ₅₅₉. This mini-review gives an overview of new exciting results and their significance for understanding the structural and functional roles of Cytb ₅₅₉ in PSII.

Draft genomes assembly and annotation of Carex parvula and Carex kokanica reveals stress-specific genes

Kobresia plants are important forage resources on the Qinghai-Tibet Plateau and are essential in maintaining the ecological balance of grasslands. Therefore, it is beneficial to obtain Kobresia genome resources and study the adaptive characteristics of Kobresia plants on the Qinghai-Tibetan Plateau. Previously, we have assembled the genome of Carex littledalei (Kobresia littledalei), which is a diploid with 29 chromosomes. In this study, we assembled genomes of Carex parvula (Kobresia pygmaea) and Carex kokanica (Kobresia royleana) via using Illumina and PacBio sequencing data, which were about 783.49 Mb and 673.40 Mb in size, respectively. And 45,002 or 36,709 protein-coding genes were further annotated in the genome of C. parvula or C. kokanica. Phylogenetic analysis indicated that Kobresia in Cyperaceae separated from Poaceae about 101.5 million years ago after separated from Ananas comosus in Bromeliaceae about 117.2 million years ago. C. littledalei and C. parvula separated about 5.0 million years ago, after separated from C. kokanica about 6.2 million years ago. In this study, transcriptome data of C. parvula at three different altitudes were also measured and analyzed. Kobresia plants genomes assembly and transcriptome analysis will assist research into mechanisms of plant adaptation to environments with high altitude and cold weather.

Genome-wide association study and transcriptome analysis dissect the genetic control of silique length in Brassica napus L

BACKGROUND

Rapeseed is the third-largest oilseed crop after soybeans and palm that produces vegetable oil for human consumption and biofuel for industrial production. Silique length (SL) is an important trait that is strongly related to seed yield in rapeseed. Although many studies related to SL have been reported in rapeseed, only a few candidate genes have been found and cloned, and the genetic mechanisms regulating SL in rapeseed remain unclear. Here, we dissected the genetic basis of SL by genome-wide association studies (GWAS) combined with transcriptome analysis.

RESULTS

We identified quantitative trait locus (QTL) for SL using a recombinant inbred line (RIL) population and two independent GWAS populations. Major QTLs on chromosomes A07, A09, and C08 were stably detected in all environments from all populations. Several candidate genes related to starch and sucrose metabolism, plant hormone signal transmission and phenylpropanoid biosynthesis were detected in the main QTL intervals, such as BnaA9.CP12-2, BnaA9.NST2, BnaA7.MYB63, and BnaA7.ARF17. In addition, the results of RNA-seq and weighted gene co-expression network analysis (WGCNA) showed that starch and sucrose metabolism, photosynthesis, and secondary cell wall biosynthesis play an important role in the development of siliques.

CONCLUSIONS

We propose that photosynthesis, sucrose and starch metabolism, plant hormones, and lignin content play important roles in the development of rapeseed siliques.

High-resolution model of Arabidopsis Photosystem II reveals the structural consequences of digitonin-extraction

In higher plants, the photosynthetic process is performed and regulated by Photosystem II (PSII). Arabidopsis thaliana was the first higher plant with a fully sequenced genome, conferring it the status of a model organism; nonetheless, a high-resolution structure of its Photosystem II is missing. We present the first Cryo-EM high-resolution structure of Arabidopsis PSII supercomplex with average resolution of 2.79 Å, an important model for future PSII studies. The digitonin extracted PSII complexes demonstrate the importance of: the LHG2630-lipid-headgroup in the trimerization of the light-harvesting complex II; the stabilization of the PsbJ subunit and the CP43-loop E by DGD520-lipid; the choice of detergent for the integrity of membrane protein complexes. Furthermore, our data shows at the anticipated Mn₄CaO₅-site a single metal ion density as a reminiscent early stage of Photosystem II photoactivation.

Transcriptomics of Biostimulation of Plants Under Abiotic Stress

Plant biostimulants are compounds, living microorganisms, or their constituent parts that alter plant development programs. The impact of biostimulants is manifested in several ways: via morphological, physiological, biochemical, epigenomic, proteomic, and transcriptomic changes. For each of these, a response and alteration occur, and these alterations in turn improve metabolic and adaptive performance in the environment. Many studies have been conducted on the effects of different biotic and abiotic stimulants on plants, including many crop species. However, as far as we know, there are no reviews available that describe the impact of biostimulants for a specific field such as transcriptomics, which is the objective of this review. For the commercial registration process of products for agricultural use, it is necessary to distinguish the specific impact of biostimulants from that of other legal categories of products used in agriculture, such as fertilizers and plant hormones. For the chemical or biological classification of biostimulants, the classification is seen as a complex issue, given the great diversity of compounds and organisms that cause biostimulation. However, with an approach focused on the impact on a particular field such as transcriptomics, it is perhaps possible to obtain a criterion that allows biostimulants to be grouped considering their effects on living systems, as well as the overlap of the impact on metabolism, physiology, and morphology occurring between fertilizers, hormones, and biostimulants.

Analysis of the transformation effect in cytochrome b559 of photosystem II in terms of the model of the heme-quinone redox interaction

Transformation of three-component redox pattern of cytochrome (Cyt) b559 in PS II membrane fragments upon various treatments is manifested in decrease of the relative content (R) of the high potential (HP) redox form of Cyt b559 and concomitant increase in the fractions of the two lower potential forms. Redox titration of Cyt b559 in different types of PS II membrane preparations was performed and revealed that (1) alteration of redox titration curve of Cyt b559 upon treatment of a sample is not specific to the type of treatment; (2) each value of R_HP defines the individual shape of the redox titration curve; (3) population of Cyt b559 may exist in several stable forms with multicomponent redox pattern: three types of three-component redox pattern and one type of two-component redox pattern as well as in the form with a single E_m; (4) transformation of Cyt b559 proceeds as successive conversion between the stable forms with multicomponent redox pattern; (5) upon harsh treatments, Cyt b559 abruptly converts into the state with a single E_m which value is intermediate between the E_m values of the two lower potential forms. Analysis of the data using the model of Cyt b559-quinone redox interaction revealed that diminution of R_HP in a range from 80 to 10% reflects a shift in redox equilibrium between the heme group of Cyt b559 and the interacting quinone, due to a gradual decrease of 90 mV in E_m of the heme group at the virtually unchanged E_m of the quinone component.

Electromagnetic Radiation Disturbed the Photosynthesis of Microcystis aeruginosa at the Proteomics Level

Photosynthesis of Microcystis aeruginosa under Electromagnetic Radiation (1.8 GHz, 40 V/m) was studied by using the proteomics. A total of 30 differentially expressed proteins, including 15 up-regulated and 15 down-regulated proteins, were obtained in this study. The differentially expressed proteins were significantly enriched in the photosynthesis pathway, in which the protein expression levels of photosystems II cytochrome b559 α subunit, cytochrome C550, PsbY, and F-type ATP synthase (a, b) decreased. Our results indicated that electromagnetic radiation altered the photosynthesis-related protein expression levels, and aimed at the function of photosynthetic pigments, photosystems II potential activity, photosynthetic electron transport process, and photosynthetic phosphorylation process of M. aeruginosa. Based on the above evidence, that photoreaction system may be deduced as a target of electromagnetic radiation on the photosynthesis in cyanobacteria; the photoreaction system of cyanobacteria is a hypothetical "shared target effector" that responds to light and electromagnetic radiation; moreover, electromagnetic radiation does not act on the functional proteins themselves but their expression processes.

Extensive gain and loss of photosystem I subunits in chromerid algae, photosynthetic relatives of apicomplexans

In oxygenic photosynthesis the initial photochemical processes are carried out by photosystem I (PSI) and II (PSII). Although subunit composition varies between cyanobacterial and plastid photosystems, the core structures of PSI and PSII are conserved throughout photosynthetic eukaryotes. So far, the photosynthetic complexes have been characterised in only a small number of organisms. We performed in silico and biochemical studies to explore the organization and evolution of the photosynthetic apparatus in the chromerids Chromera velia and Vitrella brassicaformis, autotrophic relatives of apicomplexans. We catalogued the presence and location of genes coding for conserved subunits of the photosystems as well as cytochrome b₆f and ATP synthase in chromerids and other phototrophs and performed a phylogenetic analysis. We then characterised the photosynthetic complexes of Chromera and Vitrella using 2D gels combined with mass-spectrometry and further analysed the purified Chromera PSI. Our data suggest that the photosynthetic apparatus of chromerids underwent unique structural changes. Both photosystems (as well as cytochrome b₆f and ATP synthase) lost several canonical subunits, while PSI gained one superoxide dismutase (Vitrella) or two superoxide dismutases and several unknown proteins (Chromera) as new regular subunits. We discuss these results in light of the extraordinarily efficient photosynthetic processes described in Chromera.

Different adaptation strategies of two citrus scion/rootstock combinations in response to drought stress

Scion/rootstock interaction is important for plant development and for breeding programs. In this context, polyploid rootstocks presented several advantages, mainly in relation to biotic and abiotic stresses. Here we analyzed the response to drought of two different scion/rootstock combinations presenting different polyploidy: the diploid (2x) and autotetraploid (4x) Rangpur lime (Citrus limonia, Osbeck) rootstocks grafted with 2x Valencia Delta sweet orange (Citrus sinensis) scions, named V/2xRL and V/4xRL, respectively. Based on previous gene expression data, we developed an interactomic approach to identify proteins involved in V/2xRL and V/4xRL response to drought. A main interactomic network containing 3,830 nodes and 97,652 edges was built from V/2xRL and V/4xRL data. Exclusive proteins of the V/2xRL and V/4xRL networks (2,056 and 1,001, respectively), as well as common to both networks (773) were identified. Functional clusters were obtained and two models of drought stress response for the V/2xRL and V/4xRL genotypes were designed. Even if the V/2xRL plant implement some tolerance mechanisms, the global plant response to drought was rapid and quickly exhaustive resulting in a general tendency to dehydration avoidance, which presented some advantage in short and strong drought stress conditions, but which, in long terms, does not allow the plant survival. At the contrary, the V/4xRL plants presented a response which strong impacts on development but that present some advantages in case of prolonged drought. Finally, some specific proteins, which presented high centrality on interactomic analysis were identified as good candidates for subsequent functional analysis of citrus genes related to drought response, as well as be good markers of one or another physiological mechanism implemented by the plants.

Production of Reactive Oxygen Species by Photosystem II as a Response to Light and Temperature Stress

The effect of various abiotic stresses on photosynthetic apparatus is inevitably associated with formation of harmful reactive oxygen species (ROS). In this review, recent progress on ROS production by photosystem II (PSII) as a response to high light and high temperature is overviewed. Under high light, ROS production is unavoidably associated with energy transfer and electron transport in PSII. Singlet oxygen is produced by the energy transfer form triplet chlorophyll to molecular oxygen formed by the intersystem crossing from singlet chlorophyll in the PSII antennae complex or the recombination of the charge separated radical pair in the PSII reaction center. Apart to triplet chlorophyll, triplet carbonyl formed by lipid peroxidation transfers energy to molecular oxygen forming singlet oxygen. On the PSII electron acceptor side, electron leakage to molecular oxygen forms superoxide anion radical which dismutes to hydrogen peroxide which is reduced by the non-heme iron to hydroxyl radical. On the PSII electron donor side, incomplete water oxidation forms hydrogen peroxide which is reduced by manganese to hydroxyl radical. Under high temperature, dark production of singlet oxygen results from lipid peroxidation initiated by lipoxygenase, whereas incomplete water oxidation forms hydrogen peroxide which is reduced by manganese to hydroxyl radical. The understanding of molecular basis for ROS production by PSII provides new insight into how plants survive under adverse environmental conditions.

Production of Reactive Oxygen Species by Photosystem II as a Response to Light and Temperature Stress

The effect of various abiotic stresses on photosynthetic apparatus is inevitably associated with formation of harmful reactive oxygen species (ROS). In this review, recent progress on ROS production by photosystem II (PSII) as a response to high light and high temperature is overviewed. Under high light, ROS production is unavoidably associated with energy transfer and electron transport in PSII. Singlet oxygen is produced by the energy transfer form triplet chlorophyll to molecular oxygen formed by the intersystem crossing from singlet chlorophyll in the PSII antennae complex or the recombination of the charge separated radical pair in the PSII reaction center. Apart to triplet chlorophyll, triplet carbonyl formed by lipid peroxidation transfers energy to molecular oxygen forming singlet oxygen. On the PSII electron acceptor side, electron leakage to molecular oxygen forms superoxide anion radical which dismutes to hydrogen peroxide which is reduced by the non-heme iron to hydroxyl radical. On the PSII electron donor side, incomplete water oxidation forms hydrogen peroxide which is reduced by manganese to hydroxyl radical. Under high temperature, dark production of singlet oxygen results from lipid peroxidation initiated by lipoxygenase, whereas incomplete water oxidation forms hydrogen peroxide which is reduced by manganese to hydroxyl radical. The understanding of molecular basis for ROS production by PSII provides new insight into how plants survive under adverse environmental conditions.