Physiological Significance of Overproduced Carotenoids in Transformants of the Cyanobacterium Synechococcus PCC7942 (original) (raw)
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Frontiers in Plant Science, 2020
The tolerance of photosynthesis to strong light increases in photosynthetic organisms during acclimation to strong light. We investigated the role of carotenoids in the protection of photosystem II (PSII) from photoinhibition after acclimation to strong light in the cyanobacterium Synechocystis sp. PCC 6803. In cells that had been grown under strong light at 1,000 mmol photons m −2 s −1 (SL), specific carotenoids, namely, zeaxanthin, echinenone, and myxoxanthophyll, accumulated at high levels, and the photoinhibition of PSII was less marked than in cells that had been grown under standard growth light at 70 mmol photons m −2 s −1 (GL). The rate of photodamage to PSII, as monitored in the presence of lincomycin, did not differ between cells grown under SL and GL, suggesting that the mitigation of photoinhibition after acclimation to SL might be attributable to the enhanced ability to repair PSII. When cells grown under GL were transferred to SL, the mitigation of photoinhibition of PSII occurred in two distinct stages: a first stage that lasted 4 h and the second stage that occurred after 8 h. During the second stage, the accumulation of specific carotenoids was detected, together with enhanced synthesis de novo of proteins that are required for the repair of PSII, such as the D1 protein, and suppression of the production of singlet oxygen (1 O 2). In the DcrtRDcrtO mutant of Synechocystis, which lacks zeaxanthin, echinenone, and myxoxanthophyll, the mitigation of photoinhibition of PSII, the enhancement of protein synthesis, and the suppression of production of 1 O 2 were significantly impaired during the second stage of acclimation. Thus, elevated levels of the specific carotenoids during acclimation to strong light appeared to protect protein synthesis from 1 O 2 , with the resultant mitigation of photoinhibition of PSII.
Carotenoids in Photosynthesis: An Historical Perspective
Advances in Photosynthesis and Respiration, 2004
This chapter presents a personal historical perspective of the role of carotenoids in photosynthesis. It leads the reader into the early literature on the carotenoids and photosynthesis that are related to the discoveries on the excitation energy transfer and, to a lesser extent, on photoprotection. Excitation energy transfer from the carotenoid fucoxanthin to chlorophyll (Chl) a was shown first in the diatoms by H. Dutton, W. M. Manning and B. M. Duggar, in 1943, at the University of Wisconsin at Madison. After the extensive researches of E. C. Wassink (in the Netherlands) on this topic, the classical doctoral thesis of L. N. M. Duysens became available in 1952, at the State University in Utrecht. This thesis dealt with the evidence of excitation energy transfer in many photosynthetic systems, including anoxygenic photosynthetic bacteria. The experiments of R. Emerson and C. M. Lewis, done at the Carnegie Institute of Washington, Stanford, California, in the 1940s, dealt with the quantum yield action spectra of photosynthesis. In these experiments, the famous red drop phenomenon was discovered; further, the authors showed here the low efficiency of carotenoids in the photosynthesis of both green algae and blue-green algae (cyanobacteria). In 1956, R. Stanier and his coworkers discovered, at the University of California at Berkeley, a special role of carotenoids in protection against death in phototrophic bacteria. Finally, in 1962, H. Yamamoto (of Hawaii) pioneered the role of xanthophyll cycle pigments in photoprotection. This was followed by key experiments and concepts from B. Demmig-Adams (1987, now in Colorado), and O. Björkman (at Stanford, California), among others mentioned in the text. In 1954, a 515 nm absorbance change was discovered by Duysens (1954) and has now become a quantitative measure of the membrane potential changes in photosynthesis. Historical aspects of some of the basic principles of light absorption and excitation energy transfer, and references to selected current literature are also included in this chapter to allow the reader to link the past with the present.
Frontiers in Microbiology
Carotenoids in cyanobacteria play an important role in protecting against and in repairing damage against low level UV-B radiation. Here we use transcriptomics and metabolomic HPLC pigment analysis to compare carotenoid pathway regulation in the filamentous cyanobacterium Chlorogloeopsis fritschii PCC 6912 exposed to white light and to white light supplemented with low level UV-B. Under UV-B changes in carotenoid transcription regulation were found associated with carotenogenesis (carotenoid synthesis), photoprotection and carotenoid cleavage. Transcriptional regulation was reflected in corresponding pigment signatures. All carotenogenesis pathway genes from geranylgeranyl-diphosphate to lycopene were upregulated. There were significant increases in expression of gene homologs (crtW, crtR, cruF, and cruG) associated with routes to ketolation to produce significant increases in echinenone and canthaxanthin concentrations. There were gene homologs for four β-caroteneketolases (crtO and crtW) present but only one crtW was upregulated. Putative genes encoding enzymes (CruF, CrtR, and CruG) for the conversion of γ-carotene to myxol 2-methylpentoside were upregulated. The hydroxylation pathway to nostaxanthin via zeaxanthin and caloxanthin (gene homologs for CrtR and CrtG) were not upregulated, reflected in the unchanged corresponding pigment concentrations in zeaxanthin, caloxanthin and nostaxanthin, Transcripts for the non-photochemical quenching related Orange-Carotenoid-Protein (OCP) and associated Fluoresence-Recovery-Protein (FRP) associated with photoprotection were upregulated, and one carotenoid binding Helical-Carotenoid-Protein (HCP) gene homolog was downregulated. Multiple copies of genes encoding putative apocarotenoid related carotenoid oxygenases responsible for carotenoid cleavage were identified, including an upregulated apo-β-carotenaloxygenase gene homologous to a retinal producing enzyme. Our study provides holistic insight into the photoregulatory processes that modulate the synthesis,
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2012
In cyanobacteria, the thermal dissipation of excess absorbed energy at the level of the phycobilisome (PBS)-antenna is triggered by absorption of strong blue-green light by the photoactive orange carotenoid protein (OCP). This process known as non-photochemical quenching, whose molecular mechanism remains in many respects unclear, is revealed in vivo as a decrease in phycobilisome fluorescence. In vitro reconstituted system on the interaction of the OCP and the PBS isolated from the cyanobacterium Synechocystis sp. PCC 6803 presents evidence that the OCP is not only a photosensor, but also an effecter that makes direct contacts with the PBS and causes dissipation of absorbed energy. To localize the site(s) of quenching, we have analyzed the role of chromophorylated polypeptides of the PBS using PBS-deficient mutants in conjunction with in vitro systems of assembled PBS and of isolated components of the PBS core. The results demonstrated that L CM , the core-membrane linker protein and terminal emitter of the PBS, could act as the docking site for OCP in vitro. The ApcD and ApcF terminal emitters of the PBS core are not directly subjected to quenching. The data suggests that there could be close contact between the phycocyanobilin chromophore of L CM and the 3′-hydroxyechinenone chromophore present in OCP and that L CM could be involved in OCP-induced quenching. According to the reduced average lifetime of the PBS-fluorescence and linear dependence of fluorescence intensity of the PBS on OCP concentration, the quenching has mostly dynamic character. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.
Photosynthesis Research, 2017
Upon high light excitation in photosynthetic bacteria various triplet states of pigments can accumulate leading to harmful effects. Here, the generation and lifetime of flash-induced carotenoid triplets (3 Car) have been studied by observation of the quenching of bacteriochlorophyll (BChl) fluorescence in different strains of photosynthetic bacteria including Rvx. gelatinosus (anaerobic and semianaerobic), Rsp. rubrum, Thio. roseopersicina, Rba. sphaeroides 2.4.1 and carotenoid and cytochrome deficient mutants Rba. sphaeroides Ga, R-26 and cycA, respectively. The following results were obtained: 1) 3 Car quenching is observed during and not exclusively after the photochemical rise of the fluorescence yield of BChl indicating that the charge separation in the reaction center (RC) and the carotenoid triplet formation are not consecutive but parallel processes. 2) The photo-protective function of 3 Car is not limited to the RC only and can be described by a model in which the carotenoids are distributed in the lake of the BChl pigments. 3) The observed lifetime of 3 Car in intact cells is the weighted average of the lifetimes of the carotenoids with various numbers of conjugated double bonds in the bacterial strain. 4) The lifetime of 3 Car measured in the light is significantly shorter (1-2 μs) than that measured in the dark (2-10 μs). The difference reveals the importance of the dynamics of 3 Car before relaxation. The results will be discussed not only in terms of energy levels of the 3 Car but also in terms of the kinetics of transitions among different sublevels in the excited triplet state of the carotenoid.
Plant and Cell …, 2010
The crtB gene of Synechocystis sp. PCC 6803, encoding phytoene synthase, was inactivated in the ∆ crtH mutant to generate a carotenoidless ∆ crtH/B double mutant. ∆ crtH mutant cells were used because they had better transformability than wild-type cells, most probably due to their adaptation to partial carotenoid defi ciency. Cells of the ∆ crtH/B mutant were light sensitive and could grow only under light-activated heterotrophic growth conditions in the presence of glucose. Carotenoid defi ciency did not signifi cantly affect the cellular content of phycobiliproteins while the chlorophyll content of the mutant cells decreased. The mutant cells exhibited no oxygen-evolving activity, suggesting the absence of photochemically active PSII complexes. This was confi rmed by 2D electrophoresis of photosynthetic membrane complexes. Analyses identifi ed only a small amount of a non-functional PSII core complex lacking CP43, while the monomeric and dimeric PSII core complexes were absent. On the other hand, carotenoid defi ciency did not prevent formation of the cytochrome b 6 f complex and PSI, which predominantly accumulated in the monomeric form. Radioactive labeling revealed very limited synthesis of inner PSII antennae, CP47 and especially CP43. Thus, carotenoids are indispensable constituents of the photosynthetic apparatus, being essential not only for antioxidative protection but also for the effi cient synthesis and accumulation of photosynthetic proteins and especially that of PSII antenna subunits.
Plant Biotechnology Reports, 2010
Expression of the genes for carotenoid biosynthesis (crt) is dependent on light, but little is known about the underlying mechanism of light sensing and signalling in the cyanobacterium Synechocystis sp. PCC 6803 (hereafter, Synechocystis). In the present study, we investigated the light-induced increase in the transcript levels of Synechocystis crt genes, including phytoene synthase (crtB), phytoene desaturase (crtP), f-carotene desaturase (crtQ), and b-carotene hydroxylase (crtR), during a darkto-light transition period. During the dark-to-light shift, the increase in the crt transcript levels was not affected by mutations in cyanobacterial photoreceptors, such as phytochromes (cph1, cph2 and cph3) and a cryptochrome-type photoreceptor (ccry), or respiratory electron transport components NDH and Cyd/CtaI. However, treatment with photosynthetic electron transport inhibitors significantly diminished the accumulation of crt gene transcripts. Therefore, the light induction of the Synechocystis crt gene expression is most likely mediated by photosynthetic electron transport rather than by cyanobacterial photoreceptors during the dark-to-light transition.
Plant and Cell Physiology
Orange carotenoid protein (OCP) plays a vital role in the thermal dissipation of excitation energy in the photosynthetic machinery of the cyanobacterium Synechocystis sp. PCC 6803. To clarify the role of OCP in the protection of PSII from strong light, we generated an OCP-overexpressing strain of Synechocystis and examined the effects of overexpression on the photoinhibition of PSII. In OCP-overexpressing cells, thermal dissipation of energy was enhanced and the extent of photoinhibition of PSII was reduced. However, photodamage to PSII, as monitored in the presence of lincomycin, was unaffected, suggesting that overexpressed OCP protects the repair of PSII. Furthermore, the synthesis de novo of proteins in thylakoid membranes, such as the D1 protein which is required for the repair of PSII, was enhanced in OCP-overexpressing cells under strong light, while the production of singlet oxygen was suppressed. Thus, the enhanced thermal dissipation of energy via overexpressed OCP might support the repair of PSII by protecting protein synthesis from oxidative damage by singlet oxygen under strong light, with the resultant mitigation of photoinhibition of PSII.