| 1. |
- Alexandersson, Erik, et al.
(författare)
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Arabidopsis Plasma Membrane Proteomics Identifies Components of Transport, Signal Transduction and Membrane Trafficking
- 2004
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Ingår i: Plant and Cell Physiology. - : Oxford University Press (OUP). - 1471-9053 .- 0032-0781. ; 45:11, s. 1543-1556
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Tidskriftsartikel (refereegranskat)abstract
- In order to identify integral proteins and peripheral proteins associated with the plasma membrane, highly purified Arabidopsis plasma membranes from green tissue (leaves and petioles) were analyzed by mass spectrometry. Plasma membranes were isolated by aqueous two-phase partitioning, which yields plasma membrane vesicles with a cytoplasmic-side-in orientation and with a purity of 95%. These vesicles were turned inside-out by treatment with Brij 58 to remove soluble contaminating proteins enclosed in the vesicles and to remove loosely bound contaminating proteins. In total, 238 putative plasma membrane proteins were identified, of which 114 are predicted to have transmembrane domains or to be glycosyl phosphatidylinositol anchored. About two-thirds of the identified integral proteins have not previously been shown to be plasma membrane proteins. Of the 238 identified proteins, 76% could be classified according to function. Major classes are proteins involved in transport (17%), signal transduction (16%), membrane trafficking (9%) and stress responses (9%). Almost a quarter of the proteins identified in the present study are functionally unclassified and more than half of these are predicted to be integral.
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| 2. |
- Alm Rosenblad, Magnus, 1957, et al.
(författare)
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Identification of chloroplast signal recognition particle RNA genes.
- 2004
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Ingår i: Plant & cell physiology. - : Oxford University Press (OUP). - 0032-0781 .- 1471-9053. ; 45:11, s. 1633-9
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Tidskriftsartikel (refereegranskat)abstract
- The signal recognition particle (SRP) is a ribonucleoprotein complex responsible for targeting proteins to the ER membrane in eukaryotes, the plasma membrane in bacteria and the thylakoid membrane in chloroplasts. In higher plants two different SRP-dependent mechanisms have been identified: one post-translational for proteins imported to the chloroplast and one co-translational for proteins encoded by the plastid genome. The post-translational chloroplast SRP (cpSRP) consists of the protein subunits cpSRP54 and cpSRP43. An RNA component has not been identified and does not seem to be required for the post-translational cpSRP. The co-translational mechanism is known to involve cpSRP54, but an RNA component has not yet been identified. Several chloroplast genomes have been sequenced recently, making a phylogenetically broad computational search for cpSRP RNA possible. We have analysed chloroplast genomes from 27 organisms. In higher plant chloroplasts, no SRP RNA genes were identified. However, eight plastids from red algae and Chlorophyta were found to contain an SRP RNA gene. These results suggest that SRP RNA forms a complex in these plastids with cpSRP54, reminiscent of the eubacterial SRP.
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| 3. |
- Alsterfjord, Magnus, et al.
(författare)
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Plasma membrane H+-ATPase and 14-3-3 Isoforms of Arabidopsis leaves: Evidence for isoform specificity in the 14-3-3/H+-ATPase interaction
- 2004
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Ingår i: Plant and Cell Physiology. - : Oxford University Press (OUP). - 1471-9053 .- 0032-0781. ; 45:9, s. 1202-1210
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Tidskriftsartikel (refereegranskat)abstract
- The plasma membrane H+-ATPase is activated by binding of 14-3-3 protein to the phosphorylated C terminus. Considering the large number of 14-3-3 and H+-ATPase isoforms in Arabidopsis (13 and 11 expressed genes, respectively), specificity in binding may exist between 14-3-3 and H+-ATPase isoforms. We now show that the H'-ATPase is the main target for 14-3-3 binding at the plasma membrane, and that all twelve 14-3-3 istiforms tested bind to the H+-ATPase in vitro. Using specific antibodies for nine of the 14-3-3 isoforms, we show that GF14epsilon, mu, lambda, omega, chi, phi, nu, and upsilon are present in leaves, but that isolated plasma membranes lack GF14chi, phi and upsilon. Northern blots using isoform-specific probes for all 14-3-3 and H+-ATPase isoforms showed that transcripts were present for most of the isoforms. Based on mRNA levels, GF14epsilon, mu, lambda and chi are highly expressed 14-3-3 isoforms, and AHA1, 3, and 11 highly expressed H+-ATPase isoforms in leaves. However, mass peptide fingerprinting identified AHA1 and 2 with the highest score, and their presence could be confirmed by MS/MS. It may be calculated that under 'unstressed' conditions less than one percent of total 14-3-3 is attached to the H+-ATPase. However, during a condition requiring full activation of H+ pumping, as induced here by the presence of the fungal toxin fusicoccin, several percent of total 14-3-3 may be engaged in activation of the H+-ATPase.
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| 4. |
- Christensen, Anna, et al.
(författare)
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Functional characterization of Arabidopsis calreticulin1a : a key alleviator of endoplasmic reticulum stress
- 2008
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Ingår i: Plant and Cell Physiology. - : Oxford University Press. - 0032-0781 .- 1471-9053. ; 49:6, s. 912-924
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Tidskriftsartikel (refereegranskat)abstract
- The chaperone calreticulin plays important roles in a variety of processes in the endoplasmic reticulum (ER) of animal cells, such as Ca2+ signaling and protein folding. Although the functions of calreticulin are well characterized in animals, only indirect evidence is available for plants. To increase our understanding of plant calreticulins we introduced one of the Arabidopsis isoforms, AtCRT1a, into calreticulin-deficient (crt–/–) mouse embryonic fibroblasts. As a result of calreticulin deficiency, the mouse crt–/– fibroblasts have decreased levels of Ca2+ in the ER and impaired protein folding abilities. Expression of the AtCRT1a in mouse crt–/– fibroblasts rescued these phenotypes, i.e. AtCRT1a restored the Ca2+-holding capacity and chaperone functions in the ER of the mouse crt–/– fibroblasts, demonstrating that the animal sorting machinery was also functional for a plant protein, and that basic calreticulin functions are conserved across the Kingdoms. Expression analyses using a β-glucuronidase (GUS)–AtCRT1a promoter construct revealed high expression of CRT1a in root tips, floral tissues and in association with vascular bundles. To assess the impact of AtCRT1a in planta, we generated Atcrt1a mutant plants. The Atcrt1a mutants exhibited increased sensitivity to the drug tunicamycin, an inducer of the unfolded protein response. We therefore conclude that AtCRT1a is an alleviator of the tunicamycin-induced unfolded protein response, and propose that the use of the mouse crt–/– fibroblasts as a calreticulin expression system may prove useful to assess functionalities of calreticulins from different species.
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| 5. |
- Curien, Gilles, et al.
(författare)
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The Water to Water Cycles in Microalgae.
- 2016
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Ingår i: Plant and Cell Physiology. - : Oxford University Press (OUP). - 0032-0781 .- 1471-9053. ; 57:7, s. 1354-1363
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Tidskriftsartikel (refereegranskat)abstract
- In oxygenic photosynthesis, light produces ATP plus NADPH via linear electron transfer, i.e. the in-series activity of the two photosystems: PSI and PSII. This process, however, is thought not to be sufficient to provide enough ATP per NADPH for carbon assimilation in the Calvin-Benson-Bassham cycle. Thus, it is assumed that additional ATP can be generated by alternative electron pathways. These circuits produce an electrochemical proton gradient without NADPH synthesis, and, although they often represent a small proportion of the linear electron flow, they could have a huge importance in optimizing CO2 assimilation. In Viridiplantae, there is a consensus that alternative electron flow comprises cyclic electron flow around PSI and the water to water cycles. The latter processes include photosynthetic O2 reduction via the Mehler reaction at PSI, the plastoquinone terminal oxidase downstream of PSII, photorespiration (the oxygenase activity of Rubisco) and the export of reducing equivalents towards the mitochondrial oxidases, through the malate shuttle. In this review, we summarize current knowledge about the role of the water to water cycles in photosynthesis, with a special focus on their occurrence and physiological roles in microalgae.
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| 6. |
- Ekelund, Nils, 1956-, et al.
(författare)
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Photomovement and photobleaching in two Gyrodinium species
- 1988
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Ingår i: Plant and Cell Physiology. - : Oxford University Press (OUP). - 0032-0781 .- 1471-9053. ; 29, s. 1109-1114
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Tidskriftsartikel (refereegranskat)abstract
- The phototactic orientation in Gyrodinium dorsum and G. aureolum has been analyzed. Both species show only positive phototaxis with an optimum at about 300 W-m–2. The mechanism of photoorientation does not seem to be based on a dichroic orientation of the photoreceptor pigments as in the flagellate Euglena gracilis. Photobleaching experiments have shown a far higher resistance toward continuous irradiation at even high fluence rates than in other flagellates which is in good agreement with the exclusive behavior of positive phototaxis.
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| 7. |
- Fernandez-Santos, R, et al.
(författare)
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Protein Profiles of Lipid Droplets during the Hypersensitive Defense Response of Arabidopsis against Pseudomonas Infection
- 2020
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Ingår i: Plant & cell physiology. - : Oxford University Press (OUP). - 1471-9053 .- 0032-0781. ; 61:6, s. 1144-1157
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Tidskriftsartikel (refereegranskat)abstract
- Lipid droplets (LDs) have classically been viewed as seed storage particles, yet they are now emerging as dynamic organelles associated with developmental and stress responses. Nevertheless, their involvement in plant immunity has still been little studied. Here, we found LD accumulation in Arabidopsis thaliana leaves that induced a hypersensitive response (HR) after Pseudomonas infection. We established a protocol to reproducibly isolate LDs and to analyze their protein content. The expression of GFP fusion proteins in Nicotiana benthamiana and in transgenic Arabidopsis lines validated the LD localization of glycerol-3-phosphate acyltransferase 4 (GPAT4) and 8 (GPAT8), required for cutin biosynthesis. Similarly, we showed LD localization of α-dioxygenase1 (α-DOX1) and caleosin3 (CLO3), involved in the synthesis of fatty acid derivatives, and that of phytoalexin-deficient 3 (PAD3), which is involved in camalexin synthesis. We found evidence suggesting the existence of different populations of LDs, with varying protein contents and distributions. GPAT4 and GPAT8 were associated with LDs inside stomata and surrounding cells of untreated leaves, yet they were mainly confined to LDs in guard cells after bacterial inoculation. By contrast, α-DOX1 and PAD3 were associated with LDs in the epidermal cells of HR-responding leaves, with PAD3 mostly restricted to cells near dead tissue, while CLO3 had a more ubiquitous distribution. As such, the nature of the proteins identified, together with the phenotypic examination of selected mutants, suggests that LDs participate in lipid changes and in the production and transport of defense components affecting the interaction of plants with invading pathogens.
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| 8. |
- Garcia Cerdan, Jose Gines, 1977-, et al.
(författare)
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Antisense inhibition of the PsbX protein affects PSII integrity in the higher plant Arabidopsis Thaliana
- 2009
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Ingår i: Plant and Cell Physiology. - : Oxford University Press. - 0032-0781 .- 1471-9053. ; 50:2, s. 191-202
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Tidskriftsartikel (refereegranskat)abstract
- PSII, the oxygen-evolving complex of photosynthetic organisms, contains an intriguingly large number of low molecular weight proteins. PsbX, one of these proteins, is ubiquitous in PSII complexes of cyanobacteria and plants. In previous studies, deletion of the PsbX protein in cyanobacteria has not resulted in clear phenotypic changes. Here we report the construction of an antisense (AS-PsbX) line in Arabidopsis thaliana with <10% of wild-type PsbX levels. AS-PsbX plants are capable of photoautotrophic growth, but biochemical, biophysical and immunological evidence demonstrates that reduction of PsbX contents leads to reduced levels of functional assembled PSII core complexes, while the light-harvesting antennae are not affected. In addition, levels of phosphorylation of the core proteins D1, D2 and CP43 are severely reduced in the antisense plants relative to their wild-type counterparts. We conclude that PsbX is important for accumulation of functional PSII.
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| 9. |
- Gendre, Delphine, et al.
(författare)
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Cell Wall Polysaccharides are Mislocalized to the Vacuole in echidna Mutants
- 2013
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Ingår i: Plant and Cell Physiology. - : Oxford University Press (OUP). - 0032-0781 .- 1471-9053. ; 54, s. 1867-1880
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Tidskriftsartikel (refereegranskat)abstract
- During cell wall biosynthesis, the Golgi apparatus is the platform for cell wall matrix biosynthesis and the site of packaging, of both matrix polysaccharides and proteins, into secretory vesicles with the correct targeting information. The objective of this study was to dissect the post-Golgi trafficking of cell wall polysaccharides using echidna as a vesicle traffic mutant of Arabidopsis thaliana and the pectin-secreting cells of the seed coat as a model system. ECHIDNA encodes a trans-Golgi network (TGN)-localized protein, which was previously shown to be required for proper structure and function of the secretory pathway. In echidna mutants, some cell wall matrix polysaccharides accumulate inside cells, rather than being secreted to the apoplast. In this study, live cell imaging of fluorescent protein markers as well as transmission electron microscopy (TEM)/immunoTEM of cryofixed seed coat cells were used to examine the consequences of TGN disorganization in echidna mutants under conditions of high polysaccharide production and secretion. While in wild-type seed coat cells, pectin is secreted to the apical surface, in echidna, polysaccharides accumulate in post-Golgi vesicles, the central lytic vacuole and endoplasmic reticulum-derived bodies. In contrast, proteins were partially mistargeted to internal multilamellar membranes in echidna. These results suggest that while secretion of both cell wall polysaccharides and proteins at the TGN requires ECHIDNA, different vesicle trafficking components may mediate downstream events in their secretion from the TGN.
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| 10. |
- Granlund, Irene, et al.
(författare)
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The TL29 protein is lumen located, associated with PSII and not an ascorbate peroxidase
- 2009
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Ingår i: Plant and Cell Physiology. - : Oxford Journals. - 0032-0781 .- 1471-9053. ; 50:11, s. 1898-1910
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Tidskriftsartikel (refereegranskat)abstract
- The TL29 protein is one of the more abundant proteins in the thylakoid lumen of plant chloroplasts. Based on its sequence homology to ascorbate peroxidases, but without any supporting biochemical evidence, TL29 was suggested to be involved in the plant defense system against reactive oxygen species and consequently renamed to APX4. Our in vivo and in vitro analyses failed to show any peroxidase activity associated with TL29; it bound neither heme nor ascorbate. Recombinant overexpressed TL29 had no ascorbate-dependent peroxidase activity, and various mutational analyses aiming to convert TL29 into an ascorbate peroxidase failed. Furthermore, in the thylakoid lumen no such activity could be associated with TL29 and, additionally, TL29 knock-out mutants did not show any decreased peroxidase activity or increased content of radical oxygen species when grown under light stress. Instead we could show that TL29 is a lumen-located component associated with PSII.
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