摘要：
The mechanisms of cadmium toxicity to cyanobacterial photosynthesis have been extensively studied, but the response mechanisms to combinations of different cadmium concentrations and different light intensities are not yet well understood. The two principal objectives of the present work were to: 1) study the short term (5 h) toxic effects of cadmium on Synechocystis PCC6803 under three different culturing light intensity conditions; and, 2) investigate the effects of light history on Cd toxicity to Synechocystis. The maximal (capital EF, CyrillicM) and operational (capital EF, Cyrillic'M) photosystem II quantum yields, photosystem I quantum yield [Y (I)], cyclic electron flow, relative photochemical quenching (qPrel), relative non-photochemical quenching (qNrel), relative unquenched fluorescence (UQFrel), pigment contents, and cadmium uptake were evaluated when Synechocystis cells were treated with cadmium for 5 h under three different light conditions. We demonstrated that cadmium toxicity was enhanced with increasing growth light intensities due to increased cadmium uptake under higher light exposures, and the photoprotective mechanisms could not cope with cadmium and light stress under high light conditions. We also investigated Cd toxicity to Synechocystis adapted to three growth light intensities and subsequently shifted to different light intensity conditions to compare the effects of light regime shift on cadmium toxicity. We observed increased cadmium toxicity when the cells were transferred from low light to high light conditions. Interestingly, Synechocystis cells grown at high light intensities were more tolerant to cadmium than cells grown at low light intensities after the same light regime shift, due to the development of photoprotective mechanisms.
作者机构：
[Qiu, Bao-Sheng; Yang, Yi-Wen; Shang, Jin-Long; Huang, Da; Li, Zheng-Ke; Yin, Yan-Chao] Cent China Normal Univ, Sch Life Sci, Wuhan, Hubei, Peoples R China.;[Qiu, Bao-Sheng; Yang, Yi-Wen; Shang, Jin-Long; Huang, Da; Li, Zheng-Ke; Yin, Yan-Chao] Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan, Hubei, Peoples R China.;[Chen, Min] Univ Sydney, ARC Ctr Excellence Translat Photosynth, Sydney, NSW 2006, Australia.;[Chen, Min] Univ Sydney, Sch Life & Environm Sci, Sydney, NSW 2006, Australia.
通讯机构：
[Qiu, Bao-Sheng] C;[Chen, Min] U;Cent China Normal Univ, Sch Life Sci, Wuhan, Hubei, Peoples R China.;Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan, Hubei, Peoples R China.;Univ Sydney, ARC Ctr Excellence Translat Photosynth, Sydney, NSW 2006, Australia.
关键词：
Canthaxanthin;Desiccation;Helical carotenoid protein;Nostoc flagelliforme;Orange carotenoid protein;Red carotenoid protein
摘要：
The remarkable drought-resistance of the terrestrial cyanobacterium Nostoc flagelliforme (N. flagelliforme) has attracted attention for many years. In this study, we purified a group of red proteins that accumulate in dried field samples of N. flagelliforme. These red proteins contain canthaxanthin as the bound chromophore. Native-PAGE analysis revealed that the purified red proteins resolved into six visible red bands and were composed of four helical carotenoid proteins (HCPs), HCP1, HCP2, HCP3, and HCP6 (homologs to the N-terminal domain of the orange carotenoid protein (OCP)). Seven genes encode homologs of the OCP in the genome of N. flagelliforme: two full-length ocp genes (ocpx1 and ocpx2), four N-terminal domain hcp genes (hcp1, hcp2, hcp3, and hcp6), and one C-terminal domain ccp gene. The expression levels of hcp1, hcp2, and hcp6 were highly dependent on the water status of field N. flagelliforme samples, being downregulated during rehydration and upregulated during subsequent dehydration. Transcripts of ocpx2 were dominant in the dried field samples, which we confirmed by detecting the presence of OCPx2-derived peptides in the purified red proteins. The results shed light on the relationship between carotenoid-binding proteins and the desiccation resistance of terrestrial cyanobacteria, and the physiological functions of carotenoid-binding protein complexes in relation to desiccation are discussed.
作者机构：
[Qiu, Bao-Sheng; Zhang, Lu-Dan; Li, Zheng-Ke; Dai, Guo-Zheng; Yin, Yan-Chao; Zhang, Zhong-Chun] Cent China Normal Univ, Sch Life Sci, Wuhan 430079, Hubei, Peoples R China.;[Qiu, Bao-Sheng; Zhang, Lu-Dan; Li, Zheng-Ke; Dai, Guo-Zheng; Yin, Yan-Chao; Zhang, Zhong-Chun] Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Hubei, Peoples R China.;[Chen, Min] Univ Sydney, Sch Life & Environm Sci, Sydney, NSW 2006, Australia.
通讯机构：
[Qiu, Bao-Sheng] C;[Chen, Min] U;Cent China Normal Univ, Sch Life Sci, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Hubei, Peoples R China.;Univ Sydney, Sch Life & Environm Sci, Sydney, NSW 2006, Australia.
会议名称：
Light Harvesting Satellite Meeting held in conjunction with the 17th International Congress on Photosynthesis Research
会议时间：
AUG, 2016
会议地点：
Egmond aan Zee, NETHERLANDS
会议主办单位：
[Li, Zheng-Ke;Yin, Yan-Chao;Zhang, Lu-Dan;Zhang, Zhong-Chun;Dai, Guo-Zheng;Qiu, Bao-Sheng] Cent China Normal Univ, Sch Life Sci, Wuhan 430079, Hubei, Peoples R China.^[Li, Zheng-Ke;Yin, Yan-Chao;Zhang, Lu-Dan;Zhang, Zhong-Chun;Dai, Guo-Zheng;Qiu, Bao-Sheng] Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Hubei, Peoples R China.^[Chen, Min] Univ Sydney, Sch Life & Environm Sci, Sydney, NSW 2006, Australia.
关键词：
Accessory chlorophyll-binding proteins (CBPs);Iron limitation;Iron-stress-induced protein A (IsiA);Photosynthesis;Six transmembrane helix family of chlorophyll-binding proteins/antenna;Acaryochloris marina
作者机构：
[Qiu, Bao-Sheng; Jiang, Hai-Bo; Zang, Sha-Sha; Song, Wei-Yu] Cent China Normal Univ, Sch Life Sci, Wuhan 430079, Hubei, Peoples R China.;[Qiu, Bao-Sheng; Jiang, Hai-Bo; Zang, Sha-Sha; Song, Wei-Yu] Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Hubei, Peoples R China.;[Chen, Min] Univ Sydney, Sch Life & Environm Sci, Sydney, NSW 2006, Australia.
通讯机构：
[Qiu, Bao-Sheng] C;Cent China Normal Univ, Sch Life Sci, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Hubei, Peoples R China.
摘要：
The sulfur-formation (
suf
) genes play important roles in both photosynthesis and respiration of cyanobacteria, but the organism prioritizes Fe–S clusters for respiration at the expense of photosynthesis.
Iron–sulfur (Fe–S) clusters are important to all living organisms, but their assembly mechanism is poorly understood in photosynthetic organisms. Unlike non-photosynthetic bacteria that rely on the iron–sulfur cluster system, Synechocystis sp. PCC 6803 uses the Sulfur-Formation (SUF) system as its major Fe–S cluster assembly pathway. The co-expression of suf genes and the direct interactions among SUF subunits indicate that Fe–S assembly is a complex process in which no suf genes can be knocked out completely. In this study, we developed a condition-controlled SUF Knockdown mutant by inserting the petE promoter, which is regulated by Cu2+ concentration, in front of the suf operon. Limited amount of the SUF system resulted in decreased chlorophyll contents and photosystem activities, and a lower PSI/PSII ratio. Unexpectedly, increased cyclic electron transport and a decreased dark respiration rate were only observed under photoautotrophic growth conditions. No visible effects on the phenotype of SUF Knockdown mutant were observed under heterotrophic culture conditions. The phylogenetic distribution of the SUF system indicates that it has a co-evolutionary relationship with photosynthetic energy storing pathways.
通讯机构：
[Qiu, Bao-Sheng] C;Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Sch Life Sci, Wuhan 430079, Hubei, Peoples R China.
关键词：
iron deficiency;Microcystis;photosynthesis;Synechococcus;UV-B
摘要：
Iron deficiency has been considered one of the main limiting factors of phytoplankton productivity in some aquatic systems including oceans and lakes. Concomitantly, solar ultraviolet-B radiation has been shown to have both deleterious and positive impacts on phytoplankton productivity. However, how iron-deficient cyanobacteria respond to UV-B radiation has been largely overlooked in aquatic systems. In this study, physiological responses of four cyanobacterial strains (Microcystis and Synechococcus), which are widely distributed in freshwater or marine systems, were investigated under different UV-B irradiances and iron conditions. The growth, photosynthetic pigment composition, photosynthetic activity, and nonphotochemical quenching of the different cyanobacterial strains were drastically altered by enhanced UV-B radiation under iron-deficient conditions, but were less affected under iron-replete conditions. Intracellular reactive oxygen species (ROS) and iron content increased and decreased, respectively, with increased UV-B radiation under iron-deficient conditions for both Microcystis aeruginosa FACHB 912 and Synechococcus sp. WH8102. On the contrary, intracellular ROS and iron content of these two strains remained constant and increased, respectively, with increased UV-B radiation under iron-replete conditions. These results indicate that iron-deficient cyanobacteria are more susceptible to enhanced UV-B radiation. Therefore, UV-B radiation probably plays an important role in influencing primary productivity in iron-deficient aquatic systems, suggesting that its effects on the phytoplankton productivity may be underestimated in iron-deficient regions around the world.
摘要：
Microcystis sp., especially in its colonial form, is a common dominant species during cyanobacterial blooms in many iron-deficient water bodies. It is still not entirely clear, however, how the colonial forms of Microcystis acclimate to iron-deficient habitats, and the responses of unicellular and colonial forms to iron-replete and iron-deficient conditions were examined here. Growth rates and levels of photosynthetic pigments declined to a greater extent in cultures of unicellular Microcystis than in cultures of the colonial form in response to decreasing iron concentrations, resulting in the impaired photosynthetic performance of unicellular Microcystis as compared to colonial forms as measured by variable fluorescence and photosynthetic oxygen evolution. These results indicate that the light-harvesting ability and photosynthetic capacity of colonial Microcystis was less affected by iron deficiency than the unicellular form. The carotenoid contents and nonphotochemical quenching of colonial Microcystis were less reduced than those of the unicellular form under decreasing iron concentrations, indicating that the colonial morphology enhanced photoprotection and acclimation to iron-deficient conditions. Furthermore, large amounts of iron were detected in the capsular polysaccharides (CPS) of the colonies, and more iron was found to be attached to the colonial Microcystis CPS under decreasing iron conditions as compared to unicellular cultures. These results demonstrated that colonial Microcystis can acclimate to iron deficiencies better than the unicellular form, and that CPS plays an important role in their acclimation advantage in iron-deficient waters.
作者机构：
[Qiu, Bao-Sheng; Qiu, Guo-Wei; Jiang, Hai-Bo; Lou, Wen-Jing; Xu, Ning; Li, Zheng-Ke] Cent China Normal Univ, Sch Life Sci, Wuhan 430079, Hubei, Peoples R China.;[Qiu, Bao-Sheng; Qiu, Guo-Wei; Jiang, Hai-Bo; Lou, Wen-Jing; Xu, Ning; Li, Zheng-Ke] Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Hubei, Peoples R China.;[Price, Neil M.] McGill Univ, Dept Biol, 1205 Docteur Penfield, Montreal, PQ H3A 1B1, Canada.
通讯机构：
[Jiang, Hai-Bo] C;Cent China Normal Univ, Sch Life Sci, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Hubei, Peoples R China.
摘要：
The Ycf46 mutant of
Synechocystis
showed growth inhibition under low dissolved CO
2
conditions, suggesting a role for the Ycf46 protein in the process of photosynthetic CO
2
uptake and utilization.
Hypothetical chloroplast open reading frame Ycf46 proteins are highly conserved in all cyanobacterial lineages and most algal chloroplast genomes, but their exact function is still unknown. In the cyanobacterium Synechocystis sp. PCC 6803, the Ycf46 encoding gene slr0374 is part of an operon (with slr0373 and slr0376) and responds to many environmental stresses. Transcript levels of the slr0373, slr0374 and slr0376 genes were increased under a low concentration of dissolved inorganic carbon (Ci). Compared with the wild type, the mutant lacking slr0374 showed growth arrest under Ci-deficient conditions but not under iron-deficient or low-light conditions. In addition, the mutant grew more slowly than the wild type under pH 6.0 conditions in which CO2 was the dominant Ci source, indicating the mutant cells had weak CO2 uptake and/or utilization ability. Supplying a high concentration of CO2 (5 %, v/v) to the mutant restored its phenotype to the wild type level. The photosynthetic activity of the mutant was inhibited to a lesser extent by a carbonic anhydrase inhibitor than that of the wild type, which specifically blocked CO2 uptake. Inactivation of slr0374 decreased expression of the ecaB gene and reduced carbonic anhydrase activity. A subcellular localization assay indicated that the Ycf46 protein was soluble. By co-immunoprecipitation assay using Slr0374 as a bait-protein, potential interacting proteins in the size range of 30 kDa were identified. These results suggest that the Ycf46 protein plays a role in the regulation of photosynthesis in cyanobacteria, especially in CO2 uptake and utilization.
作者机构：
[Qiu, Bao-Sheng] Cent China Normal Univ, Sch Life Sci, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Hubei, Peoples R China.
通讯机构：
[Qiu, Bao-Sheng] C;Cent China Normal Univ, Sch Life Sci, Wuhan 430079, Hubei, Peoples R China.
摘要：
Synechocystis sp. PCC 6803 possesses only one sod gene, sodB, encoding iron superoxide dismutase (FeSOD). It could not be knocked out completely by direct insertion of the kanamycin resistance cassette. When the promoter of sodB in WT Synechocystis was replaced with the copper-regulated promoter PpetE, a completely segregated PpetE-sodB strain could be obtained. When this strain was cultured in copper-starved BG11 medium, the chlorophyll a content was greatly reduced, growth was seriously inhibited and the strain was nearly dead during the 8 days of growth, whilst the WT strain grew well under the same growth conditions. These results indicated that sodB was essential for photoautotrophic growth of Synechocystis. The reduction of sodB gene copies in the Synechocystis genome rendered the cells more sensitive to oxidative stress produced by methyl viologen and norflurazon. sodB still could not be knocked out completely after active expression of sodC (encoding Cu/ZnSOD) from Synechococcus sp. CC9311 in the neutral site slr0168 under the control of the psbAII promoter, which means the function of FeSOD could not be complemented completely by Cu/ZnSOD. Heterogeneously expressed sodC increased the oxidation and photoinhibition tolerance of the Synechocystis sodB knockdown mutant. Membrane fractionation followed by immunoblotting revealed that FeSOD was localized in the cytoplasm, and Cu/ZnSOD was localized in the soluble and thylakoid membrane fractions of the transformed Synechocystis. Cu/ZnSOD has a predicted N-terminal signal peptide, so it is probably a lumen protein. The different subcellular localization of these two SODs may have resulted in the failure of substitution of sodC for sodB.
摘要：
The terrestrial macroscopic cyanobacterium Nostoc commune exhibits remarkable resistance to desiccation stress. This species synthesizes abundant acidic water stress protein (WSPA) in cells upon desiccation and secretes it into the extracellular polysaccharide sheath upon rehydration. However, our knowledge about its cellular role in stress resistance is still rather limited. In this paper, we first revealed that WSPA also occurred in two other macroscopic cyanobacteria Nostoc flagelliforme and Nostoc sphaeroides, but it is more abundant in N. commune. The N. commune wspa1 gene was then heterologously expressed in Arabidopsis thaliana. Phenotypic observation found that WSPA1 conferred increased tolerance to osmotic stress in transgenic plants. The physiological indexes such as relative electrolyte leakage, malondialdehyde, proline accumulation and the maximal quantum efficiency of Photosystem II, were also improved in transgenic plants upon osmotic stress, compared to wild types. In addition, GFP fluorescence analysis of eGFP::wspa1 transgenic plant showed that WSPA1 was localized in the cytoplasm. Therefore, the role of WSPA revealed by this study mainly represented its intracellular function. In general, our research suggested that WSPA may act as a stress protein and involve cellular osmotic stress resistance.
关键词：
ammonium toxicity;oxygen evolution complex;photoinhibition;photosystem II
摘要：
Ammonium is one of the major nutrients for plants, and a ubiquitous intermediate in plant metabolism, but it is also known to be toxic to many organisms, in particular to plants and oxygenic photosynthetic microorganisms. Although previous studies revealed a link between ammonium toxicity and photodamage in cyanobacteria under in vivo conditions, ammonium-induced photodamage of photosystem II (PSII) has not yet been investigated with isolated thylakoid membranes. We show here that ammonium directly accelerated photodamage of PSII in Synechocystis sp. strain PCC6803, rather than affecting the repair of photodamaged PSII. Using isolated thylakoid membranes, it could be demonstrated that ammonium-induced photodamage of PSII primarily occurred at the oxygen evolution complex, which has a known binding site for ammonium. Wild-type Synechocystis PCC6803 cells can tolerate relatively high concentrations of ammonium because of efficient PSII repair. Ammonium tolerance requires all three psbA genes since mutants of any of the three single psbA genes are more sensitive to ammonium than wild-type cells. Even the poorly expressed psbA1 gene, whose expression was studied in some detail, plays a detectable role in ammonium tolerance.
作者机构：
[Qiu, Bao-Sheng] Cent China Normal Univ, Coll Life Sci, Wuhan, Hubei, Peoples R China.;Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan, Hubei, Peoples R China.
通讯机构：
[Qiu, Bao-Sheng] C;Cent China Normal Univ, Coll Life Sci, Wuhan, Hubei, Peoples R China.
摘要：
The phenomenon of cyanobacteria bloom occurs widely in lakes, reservoirs, ponds and slow flowing rivers. Those blooms can have important repercussions, at once on recreational and commercial activities but also on the health of animals and human beings. Indeed, many species are known to produce toxins which are released in water mainly at cellular death. The cyanotoxin most frequently encountered is the microcystin (MC), a hepatotoxin which counts more than 70 variants. The use of fast tests for the detection of this toxin is thus a necessity for the protection of the ecosystems and the human health. A promising method for their detection is a bioassay based on the chlorophyll a fluorescence of algae. Many studies have shown that algae are sensible to diverse pollutants, but were almost never used for cyanotoxins. Therefore, our goals were to evaluate the effect of microcystin on the fluorescence of different species of algae and how it can affect the flow of energy through photosystem II. To reach these objectives, we exposed four green algae (Scenedesmus obliquus CPCC5, Chlamydomonas reinhardtii CC125, Pseudokirchneriella subcapitata CPCC37 and Chlorella vulgaris CPCC111) to microcystin standards (variants MC-LF, LR, RR, YR) and to microcystin extracted from Microcystis aeruginosa (CPCC299), which is known to produce mainly MC-LR. Chlorophyll a fluorescence was measured by PEA (Plant Efficiency Analyzer) and LuminoTox. The results of our experiment showed that microcystins affect the photosynthetic efficiency and the flow of energy through photosystem II from 0.01 μg/mL, within only 15 min. From exposure to standard of microcystin, we showed that MC-LF was the most potent variant, followed by MC-YR, LR and RR. Moreover, green algae used in this study demonstrated different sensitivity to MCs, S. obliquus being the more sensitive. We finally demonstrated that LuminoTox was more sensitive to MCs than parameters measured with PEA, although the latter brings indication on the mode of action of MCs at the photosynthetic apparatus level. This is the first report showing a photosynthetic response within 15 min of exposure. Our results suggest that bioassay based on chlorophyll fluorescence can be used as a rapid and sensitive tool to detect microcystin.
摘要：
Cyanobacteria are known to survive in iron-deficient environments, but the ways in which they acquire Fe and acclimate are not completely understood. Here we report a novel gene sll1263 that is required for Synechocystis sp. strain PCC 6803 to grow under iron-deficient conditions. sll1263 encodes a putative cation diffusion facilitator protein (CDF) that shows 50% amino acid similarity with ferrous iron efflux protein (FieF) of heterotrophic bacteria. In bacteria, the gene product is involved in metal export from the cell, but in Synechocystis sll1263 plays a role in iron uptake. The results show that expression of sll1263 was induced by iron-deficient conditions and its inactivation significantly decreased the growth rate of an sll1263– mutant. Other genes known to be required for Fe acquisition were also strongly up-regulated in the mutant even in the presence of high Fe. Overexpression of sll1263 increased growth under iron deficiency but reduced growth under high-iron stress, suggesting that the gene product was involved in iron uptake rather than detoxification. Expression of FieF in the sll1263– mutant was unable to rescue the Fe-deficient phenotype, but Sll1263 completely restored it. Measurements of cellular iron content and the iron uptake rate showed that they were significantly less in the sll1263– mutant than in the wild type, consistent with a role for sll1263 in iron uptake. We hypothesize that the low-iron habitats and high-iron requirements of cyanobacteria may be the reason why cyanobacterial CDF protein functions in Fe uptake and not efflux as in non-photosynthetic bacteria.
作者机构：
[Qiu, Bao-Sheng] Cent China Normal Univ, Coll Life Sci, Wuhan 430079, Peoples R China.;Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Peoples R China.
通讯机构：
[Qiu, Bao-Sheng] C;Cent China Normal Univ, Coll Life Sci, Wuhan 430079, Peoples R China.
关键词：
detoxification;heavy metal;hyperaccumulation
摘要：
Phytochelatin (PC) synthesis is considered necessary for Cd tolerance in non-resistant plants, but roles for PCs in hyper-accumulating species are currently unknown. In the present study, the relationship between PC synthesis and Cd accumulation was investigated in the Cd hyperaccumulator Sedum alfredii Hance. PCs were most abundant in leaves followed by stems, but hardly detected by the reversed-phase high-performance liquid chromatography (HPLC) in roots. Both PC synthesis and Cd accumulation were time-dependent and a linear correlation between the two was established with about 1:15 PCs : Cd stoichiometry in leaves. PCs were found in the elution fractions, which were responsible for Cd peaks in the anion exchange chromatograph assay. About 5% of the total Cd was detected in these elution fractions as PCs were found. Most Cd was observed in the cell wall and intercellular space of leaf vascular cells. These results suggest that PCs do not detoxify Cd in roots of S. alfredii. However, like in non-resistant plants, PCs might act as the major intracellular Cd detoxification mechanism in shoots of S. alfredii.
