Evidence for protection by heat-shock proteins against photoinhibition during heat-shock

Schuster, Gadi; Even, Dena; Kloppstech, Klaus; Ohad, Itzhak

doi:10.1002/j.1460-2075.1988.tb02776.x

Cited by 106 publications

(62 citation statements)

References 19 publications

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“…Prolonged illumination induces the formation of aggregates that are so large they do not penetrate into the gel (Fig. S6) (32,33,(35)(36)(37)(38). We assessed the degree of photodamage in the different strains by comparing the disappearance rate of D1 from the 32 kDa region of the SDS/PAGE by immunoblotting.…”

Section: Resultsmentioning

confidence: 99%

Engineering of an alternative electron transfer path in photosystem II

Larom

Salama

Schuster

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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The initial steps of oxygenic photosynthetic electron transfer occur within photosystem II, an intricate pigment/protein transmembrane complex. Light-driven electron transfer occurs within a multistep pathway that is efficiently insulated from competing electron transfer pathways. The heart of the electron transfer system, composed of six linearly coupled redox active cofactors that enable electron transfer from water to the secondary quinone acceptor Q B , is mainly embedded within two proteins called D1 and D2. We have identified a site in silico, poised in the vicinity of the Q A intermediate quinone acceptor, which could serve as a potential binding site for redox active proteins. Here we show that modification of Lysine 238 of the D1 protein to glutamic acid (Glu) in the cyanobacterium Synechocystis sp. PCC 6803, results in a strain that grows photautotrophically. The Glu thylakoid membranes are able to perform light-dependent reduction of exogenous cytochrome c with water as the electron donor. Cytochrome c photoreduction by the Glu mutant was also shown to significantly protect the D1 protein from photodamage when isolated thylakoid membranes were illuminated. We have therefore engineered a novel electron transfer pathway from water to a soluble protein electron carrier without harming the normal function of photosystem II. cyanobacteria | energy conversion | proinhibition | photosynthesis | protein engineering P hotosynthesis is the major source of useful chemical energy in the biosphere. All photosynthetic processes require efficient electron transfer (ET) pathways that are utilized for proton gradient formation (to be used for the production of ATP) and/or accumulation of reducing equivalents (1, 2). Light energy, absorbed by light-harvesting antenna complexes, is transferred to photochemical reaction centers (RC), initiating charge separation in specific chlorophyll molecules bound to the RC proteins. Following charge separation, electrons are transferred sequentially to a series of acceptor molecules, each with a redox potential determined by its immediate environment (3, 4). The source of electron replenishment differs according to the reaction center type. For instance in purple non-sulfur bacteria, electrons are cycled back to the oxidized reaction center by a soluble cytochrome c (cyt c) type protein (5, 6). Oxygenic photosynthetic organisms (cyanobacteria, red and green algae and plants) contain two photosystems: photosystem I (PSI) and photosystem II (PSII) that work linearly (1, 7), and the source of electrons is water. One common facet of all ET pathways is the requirement for insulation of the redox active cofactors from potentially reducing/oxidizing molecules within the RC or in the surrounding media. Insulation provides the system with maximal ET rates and efficiencies and also prevents damage to the RC.PSII has a redox potential of up to 1.2 V (8, 9), required to abstract electrons from water (Fig. 1A). The photoexcited P 680 reaction center chlorophyll a primary donor transfers electron...

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Section: Resultsmentioning

confidence: 99%

Engineering of an alternative electron transfer path in photosystem II

Larom

Salama

Schuster

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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“…In C reinhardtii, preferential association of this protein with the thylakoid membranes was suggested to be with the grana stacks (8,12,34). This was corroborated by immunocytochemical localization of most of the 22-kD HSP in the granal fraction of thylakoid membranes isolated from heated cells (8).…”

Section: Vierling (Personal Communication)mentioning

confidence: 72%

“…Furthermore, although only a single HSP20 protein has been shown in chloroplasts for pea and maize (12,21,23,39), two exist in both soybean and C. reinhardtii. These two HSPs were the 22-kD HSP, apparently specific to dicotyledons, and a second, larger HSP of around 28 kD (34,39). Given that the monocotyledon homolog to the 22-kD HSP is 24 kD in size, it is possible that the 32-kD HSP observed in barley is homologous to the second, larger HSP of 28 kD found in soybean and C. reinhardtii.…”

Section: Vierling (Personal Communication)mentioning

confidence: 94%

The Identification of a Heat-Shock Protein Complex in Chloroplasts of Barley Leaves

Clarke¹,

Critchley²

1992

Plant Physiol.

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In vivo radiolabeling of chloroplast proteins in barley (Hordeum vulgare L. cv Corvette) leaves and their separation by one-dimensional electrophoresis revealed at least seven heat-shock proteins between 24 and 94 kD, of which most have not been previously identified in this C3 species. Fractionation into stromal and thylakoid membrane components showed that all chloroplast heat-shock proteins were synthesized on cytoplasmic ribosomes, translocated into the chloroplast, and located in the stroma. Examination of stromal preparations by native (nondissociating) polyacrylamide gel electrophoresis revealed the presence of a high-molecular mass heat-shock protein complex in barley. This chaperone molecule does not take part in the final assembled complex (31). One such molecular chaperone within the chloroplast is RBP, which mediates the correct assembly of the Rubisco holoenzyme (9, 19). Despite the high degree of sequence homology between RBP and HSP60 proteins, however, it has yet to be shown that the synthesis of RBP increases significantly during heat shock. In plant cells experiencing heat stress, many of the induced cytoplasmic HSPs aggregate into morphologically unique structures known as HSGs (21,22,[25][26][27]. HSGs appear in the cytoplasm as dense granular complexes under the electron microscope (21, 27) but exist as smaller-sized precursor particles under normal conditions. They consist of protein and RNA, with the protein component consisting of 5 to 10% of total cytosolic HSP70 and up to 80% of all HSP20 proteins synthesized during heat shock (22,25). The RNA portion consists of non-heat-shock mRNA transcribed prior to high temperatures, and heat-shock mRNA synthesized at the onset of heat stress (22,27). HSGs are thought to function as transient storage sites for non-heat-shock mRNA, preventing their degradation during heat stress (27). When temperatures are lowered after a period of heat shock, the HSGs become more dispersed and associate closely with organelles active in protein synthesis, such as polysomes. This facilitates the rapid reactivation of control mRNA translation during recovery (21).Similar riboprotein complexes occur in the nucleolus as large perichromatin granules (21,22,24,33). These HSGs contain unprocessed precursor RNA species due to the thermal inactivation of intron splicing. Like cytoplasmic HSGs, the perichromatin granules disintegrate upon recovery and the return of normal nucleolus ultrastructure and functional processing of immature RNA (24,33).As yet, no comparable HSG structure or heat-inducible molecular chaperone has been observed in chloroplasts during heat shock. A recent study, however, has reported the formation of a HSP complex (200 kD) in the stroma of pea chloroplasts (2) consisting of a well-characterized 21-kD HSP (7,12,37,39,40). This study proposed that the 200-kD complex was the functional form of the 21-kD HSP in vivo, suggesting a possible homology to the cytoplasmic HSGs (2).The aim of this study was first to identify the range of HSPs synthesi...

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“…A function in protecting the photosynthetic apparatus against heat and light stress has recently been demonstrated for shsps that are transported into the chloroplast. In Chlamydomonas, the presence of hsp22 correlates with the prevention of light-induced aggregation of the Dl protein of PSII during the heat-shock process (25). The function of the cytoplasmic shsps is not known; however, the ubiquitous nature and the complexity of these proteins argue that they have important functions under both stress and normal growth conditions.…”

Section: Identification Of the Transcription Initiationmentioning

confidence: 99%

Structure and Light-Induced Expression of a Small Heat-Shock Protein Gene of Pharbitis nil

et al. 1992

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To isolate genes that are regulated by a photoperiod that promotes flowering in Pharbitis nil, a cDNA library representing mRNA of induced cotyledons was screened by differential hybridization. The DNA sequence of one cDNA clone isolated by this approach, clone 12L, showed homology to plant small heat-shock protein (hsp) genes. P. nil genomic clones hybridizing to clone 12L were isolated, and the DNA sequences of two P. nil small hsp (shsp) genes, shsp-1 and shsp-2, were determined. The derived amino acid sequences of shsp-1 and shsp-2 showed maximum homology to the 17.9-kD soybean hsp, a member of the class 11 cytoplasmic hsps found in plants. A The physiological processes in floral initiation can be divided into three steps: photoperiodic perception by cotyledons, translocation of induced floral stimulus to the shoot tip where floral initiation takes place, and evocation that results in the commitment of the meristem to form flowers. RNA synthesis in cotyledons, in response to the inductive photoperiod, has been suggested as a necessary part of floral induction in P. nil (1, 31). Recently, more direct molecular approaches have been applied to the study of changes in gene expression associated with the photoperiodic induction of flowering. Both qualitative and quantitative differences were found between translatable mRNAs isolated from cotyledons of plants kept in continuous light and from cotyledons of plants that received an inductive dark period (16).To isolate genes whose expression in P. nil cotyledons is regulated by a photoperiod that leads to flowering, we used a differential screening procedure. We report the isolation, sequence, and expression of one of the genes isolated by this approach. We demonstrate that this gene is a member of a multigene family and can potentially encode a low molecular mass hsp4. Expression of one member of this family is regulated by heat shock and by light, and expression of a related member is regulated only by heat shock. MATERIALS AND METHODS PlantsPharbitis nil plants were grown at 230C for 5 d in coolwhite fluorescent light (145 gE m-2 s-1). At this time, they were subjected to an inductive dark period of 12 or 14 h and were subsequently kept in light for 2 h. The cotyledons were excised, and RNA was extracted as described below. Plants that received a red light night break were exposed to 20 min of red light at the 7th hour of the dark treatment.

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Evidence for protection by heat-shock proteins against photoinhibition during heat-shock

Cited by 106 publications

References 19 publications

Engineering of an alternative electron transfer path in photosystem II

Engineering of an alternative electron transfer path in photosystem II

The Identification of a Heat-Shock Protein Complex in Chloroplasts of Barley Leaves

Structure and Light-Induced Expression of a Small Heat-Shock Protein Gene of Pharbitis nil

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