| 1. |
- Ankele, Elisabeth, et al.
(författare)
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In vivo visualization of Mg-ProtoporphyrinIX, a coordinator of photosynthetic gene expression in the nucleus and the chloroplast
- 2007
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Ingår i: Plant Cell. - Rockville Pike, Bethesda MD, USA : National Center for Biotechnology Information, U.S. National Library of Medicine. - 1040-4651 .- 1532-298X. ; 19:6, s. 1964-1979
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Tidskriftsartikel (refereegranskat)abstract
- The photosynthetic apparatus is composed of proteins encoded by genes from both the nucleus and the chloroplast. To ensure that the photosynthetic complexes are assembled stoichiometrically and to enable their rapid reorganization in response to a changing environment, the plastids emit signals that regulate nuclear gene expression to match the status of the plastids. One of the plastid signals, the chlorophyll intermediate Mg-ProtoporphyrinIX (Mg-ProtoIX) accumulates under stress conditions and acts as a negative regulator of photosynthetic gene expression. By taking advantage of the photoreactive property of tetrapyrroles, Mg-ProtoIX could be visualized in the cells using confocal laser scanning spectroscopy. Our results demonstrate that Mg-ProtoIX accumulated both in the chloroplast and in the cytosol during stress conditions. Thus, the signaling metabolite is exported from the chloroplast, transmitting the plastid signal to the cytosol. Our results from the Mg-ProtoIX over- and underaccumulating mutants copper response defect and genome uncoupled5, respectively, demonstrate that the expression of both nuclear- and plastid-encoded photosynthesis genes is regulated by the accumulation of Mg-ProtoIX. Thus, stress-induced accumulation of the signaling metabolite Mg-ProtoIX coordinates nuclear and plastidic photosynthetic gene expression.
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| 2. |
- Blanco, Nicolas E., et al.
(författare)
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Dual and dynamic intracellular localization of Arabidopsis thaliana SnRK1.1
- 2019
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Ingår i: Journal of Experimental Botany. - : Oxford University Press. - 0022-0957 .- 1460-2431. ; 70:8, s. 2325-2338
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Tidskriftsartikel (refereegranskat)abstract
- Sucrose non-fermenting 1 (SNF1)-related protein kinase 1.1 (SnRK1.1; also known as KIN10 or SnRK1 alpha) has been identified as the catalytic subunit of the complex SnRK1, the Arabidopsis thaliana homologue of a central integrator of energy and stress signalling in eukaryotes dubbed AMPK/Snf1/SnRK1. A nuclear localization of SnRK1.1 has been previously described and is in line with its function as an integrator of energy and stress signals. Here, using two biological models (Nicotiana benthamiana and Arabidopsis thaliana), native regulatory sequences, different microscopy techniques, and manipulations of cellular energy status, it was found that SnRK1.1 is localized dynamically between the nucleus and endoplasmic reticulum (ER). This distribution was confirmed at a spatial and temporal level by co-localization studies with two different fluorescent ER markers, one of them being the SnRK1.1 phosphorylation target HMGR. The ER and nuclear localization displayed a dynamic behaviour in response to perturbations of the plastidic electron transport chain. These results suggest that an ER-associated SnRK1.1 fraction might be sensing the cellular energy status, being a point of crosstalk with other ER stress regulatory pathways.
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| 3. |
- Blomberg, Jeanette, et al.
(författare)
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Pseudomonas syringae infectivity correlates to altered transcript and metabolite levels of Arabidopsis mediator mutants
- 2024
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Rapid metabolic responses to pathogens are essential for plant survival and depend on numerous transcription factors. Mediator is the major transcriptional co-regulator for integration and transmission of signals from transcriptional regulators to RNA polymerase II. Using four Arabidopsis Mediator mutants, med16, med18, med25 and cdk8, we studied how differences in regulation of their transcript and metabolite levels correlate to their responses to Pseudomonas syringae infection. We found that med16 and cdk8 were susceptible, while med25 showed increased resistance. Glucosinolate, phytoalexin and carbohydrate levels were reduced already before infection in med16 and cdk8, but increased in med25, which also displayed increased benzenoids levels. Early after infection, wild type plants showed reduced glucosinolate and nucleoside levels, but increases in amino acids, benzenoids, oxylipins and the phytoalexin camalexin. The Mediator mutants showed altered levels of these metabolites and in regulation of genes encoding key enzymes for their metabolism. At later stage, mutants displayed defective levels of specific amino acids, carbohydrates, lipids and jasmonates which correlated to their infection response phenotypes. Our results reveal that MED16, MED25 and CDK8 are required for a proper, coordinated transcriptional response of genes which encode enzymes involved in important metabolic pathways for Arabidopsis responses to Pseudomonas syringae infections.
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| 4. |
- Calderon, Robert H., et al.
(författare)
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How retrograde signaling is intertwined with the evolution of photosynthetic eukaryotes
- 2021
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Ingår i: Current opinion in plant biology. - : Elsevier. - 1369-5266 .- 1879-0356. ; 63
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Forskningsöversikt (refereegranskat)abstract
- Chloroplasts and mitochondria evolved from free-living prokaryotic organisms that entered the eukaryotic cell through endosymbiosis. The gradual conversion from endosymbiont to organelle during the course of evolution was accompanied by the development of a communication system between the host and the endosymbiont, referred to as retrograde signaling or organelle-to-nucleus signaling. In higher plants, plastid-to-nucleus signaling involves multiple signaling pathways necessary to coordinate plastid function and cellular responses to developmental and environmental stimuli. Phylogenetic reconstructions using sequence information from evolutionarily diverse photosynthetic eukaryotes have begun to provide information about how retrograde signaling pathways were adopted and modified in different lineages over time. A tight communication system was likely a major facilitator of plants conquest of the land because it would have enabled the algal ancestors of land plants to better allocate their cellular resources in response to high light and desiccation, the major stressor for streptophyte algae in a terrestrial habitat. In this review, we aim to give an evolutionary perspective on plastid-to-nucleus signaling.
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| 5. |
- Crawford, Tim, et al.
(författare)
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Specific functions for Mediator complex subunits from different modules in the transcriptional response of Arabidopsis thaliana to abiotic stress
- 2020
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Adverse environmental conditions are detrimental to plant growth and development. Acclimation to abiotic stress conditions involves activation of signaling pathways which often results in changes in gene expression via networks of transcription factors (TFs). Mediator is a highly conserved co-regulator complex and an essential component of the transcriptional machinery in eukaryotes. Some Mediator subunits have been implicated in stress-responsive signaling pathways; however, much remains unknown regarding the role of plant Mediator in abiotic stress responses. Here, we use RNA-seq to analyze the transcriptional response of Arabidopsis thaliana to heat, cold and salt stress conditions. We identify a set of common abiotic stress regulons and describe the sequential and combinatorial nature of TFs involved in their transcriptional regulation. Furthermore, we identify stress-specific roles for the Mediator subunits MED9, MED16, MED18 and CDK8, and putative TFs connecting them to different stress signaling pathways. Our data also indicate different modes of action for subunits or modules of Mediator at the same gene loci, including a co-repressor function for MED16 prior to stress. These results illuminate a poorly understood but important player in the transcriptional response of plants to abiotic stress and identify target genes and mechanisms as a prelude to further biochemical characterization.
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| 6. |
- Gustafsson, Malin, et al.
(författare)
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Unlocking the secret life of blue mussels: Exploring connectivity in the Skagerrak through biophysical modeling and population genomics
- 2024
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Ingår i: Evolutionary Applications. - 1752-4571. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of functional dispersal barriers in the marine environment can be used to inform a wide variety of management actions, such as marine spatial planning, restoration efforts, fisheries regulations, and invasive species management. Locations and causes of dispersal barriers can be studied through various methods, including movement tracking, biophysical modeling, demographic models, and genetics. Combining methods illustrating potential dispersal, such as biophysical modeling, with realized dispersal through, e.g., genetic connectivity estimates, provides particularly useful information for teasing apart potential causes of observed barriers. In this study, we focus on blue mussels (Mytilus edulis) in the Skagerrak—a marginal sea connected to the North Sea in Northern Europe—and combine biophysical models of larval dispersal with genomic data to infer locations and causes of dispersal barriers in the area. Results from both methods agree; patterns of ocean currents are a major structuring factor in the area. We find a complex pattern of source-sink dynamics with several dispersal barriers and show that some areas can be isolated despite an overall high dispersal capability. Finally, we translate our finding into management advice that can be used to sustainably manage this ecologically and economically important species in the future.
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| 7. |
- Hermida-Carrera, Carmen, et al.
(författare)
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CDK8 of the mediator kinase module connects leaf development to the establishment of correct stomata patterning by regulating the levels of the transcription factor SPEECHLESS (SPCH)
- 2024
-
Ingår i: Plant, Cell and Environment. - : John Wiley & Sons. - 0140-7791 .- 1365-3040.
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Tidskriftsartikel (refereegranskat)abstract
- The components of the mediator kinase module are highly conserved across all eukaryotic lineages, and cyclin-dependent kinase 8 (CDK8) is essential for correct cell proliferation and differentiation in diverse eukaryotic systems. We show that CDK8 couples leaf development with the establishment of correct stomata patterning for prevailing CO2 conditions. In Arabidopsis, the basic helix-loop-helix (bHLH) transcription factor SPEECHLESS (SPCH) controls cellular entry into the stomatal cell lineage, and CDK8 interacts with and phosphorylates SPCH, controlling SPCH protein levels and thereby also expression of the SPCH target genes encoding key regulators of cell fate and asymmetric cell divisions. The lack of the CDK8-mediated control of SPCH results in an increased number of meristemoid and guard mother cells, and increased stomata index in the cdk8 mutants. Increasing atmospheric CO2 concentrations trigger a developmental programme controlling cell entry into stomatal lineage by limiting the asymmetric divisions. In cdk8, the number of meristemoids and guard mother cells remains the same under ambient and high CO2 concentrations, as the accumulated levels of SPCH caused by the lack of CDK8 appear to override the negative regulation of increased CO2. Thus, our work provides novel mechanistic understanding of how plants alter critical leaf properties in response to increasing atmospheric CO2.
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| 8. |
- Hernandez-Verdeja, Tamara, et al.
(författare)
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Emerging from the darkness : interplay between light and plastid signaling during chloroplast biogenesis
- 2020
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 169:3, s. 397-406
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Tidskriftsartikel (refereegranskat)abstract
- Chloroplast biogenesis is a highly complex process that requires carefully coordinated communication between the nucleus and the chloroplast to integrate light signaling and information about the state of the plastid through retrograde signals. Most studies on plastid development have been performed using dark-grown seedlings and have focused on the transition from etioplast to chloroplast in response to light. Some advances are now also being made to understand the transition directly from proplastids to chloroplasts as it occurs in the shoot apical meristems. Recent reports have highlighted the importance of repressive mechanisms to block premature chloroplast development in dark, both at the transcriptional and post-transcriptional level. A group of new proteins with dual plastid and nuclear localization were shown to take part in the light triggered degradation of PHYTOCHROME INTERACTING FACTORs (PIFs) in the nucleus and thereby release the suppression of the nuclear photosynthesis associated genes. These dually localized proteins are also required to activate transcription of photosynthesis genes in the plastid in response to light, emphasizing the close link between the nucleus and the plastids during early light response. Furthermore, development of a fully functional chloroplast requires a plastid signal but the nature of this signal(s) is still unknown. GENOMES UNCOUPLED1 (GUN1) is a plastid protein pivotal for retrograde signal(s) during early seedling development, and recent reports have revealed multiple interactors of GUN1 from different plastid processes. These new GUN1 interactors could reveal the true molecular function of the enigmatic character, GUN1, under naturally occurring adverse growth conditions.
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| 9. |
- Hernández-Verdeja, Tamara, et al.
(författare)
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GENOMES UNCOUPLED1 plays a key role during the de-etiolation process in Arabidopsis
- 2022
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Ingår i: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 235:1, s. 188-203
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Tidskriftsartikel (refereegranskat)abstract
- One of the most dramatic challenges in the life of a plant occurs when the seedling emerges from the soil and exposure to light triggers expression of genes required for establishment of photosynthesis.This process needs to be tightly regulated, as premature accumulation of light-harvesting proteins and photoreactive Chl precursors causes oxidative damage when the seedling is first exposed to light. Photosynthesis genes are encoded by both nuclear and plastid genomes, and to establish the required level of control, plastid-to-nucleus (retrograde) signalling is necessary to ensure correct gene expression.We herein show that a negative GENOMES UNCOUPLED1 (GUN1)-mediated retrograde signal restricts chloroplast development in darkness and during early light response by regulating the transcription of several critical transcription factors linked to light response, photomorphogenesis, and chloroplast development, and consequently their downstream target genes in Arabidopsis.Thus, the plastids play an essential role during skotomorphogenesis and the early light response, and GUN1 acts as a safeguard during the critical step of seedling emergence from darkness.
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| 10. |
- Ji, Yan, et al.
(författare)
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A fully assembled plastid-encoded RNA polymerase complex detected in etioplasts and proplastids in Arabidopsis
- 2021
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Ingår i: Physiologia Plantarum. - : John Wiley & Sons. - 0031-9317 .- 1399-3054. ; 171:3, s. 435-446
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Tidskriftsartikel (refereegranskat)abstract
- The plastid-encoded genes of higher plants are transcribed by at least two types of RNA polymerases, the nuclear-encoded RNA polymerase (NEP) and the plastid-encoded RNA polymerase (PEP). In mature photosynthesizing leaves, the vast majority of the genes are transcribed by PEP. However, the regulatory mechanisms controlling plastid transcription during early light response is unclear. Chloroplast development is suggested to be associated with a shift in the usage of the primary RNA polymerase from NEP to PEP as the expression of the plastid-encoded photosynthesis genes is induced upon light exposure. Assembly of the PEP complex has been suggested as a rate-limiting step for full activation of plastid-encoded photosynthesis gene expression. However, two sigma factor mutants, sig2 and sig6, with reduced PEP activity, showed significantly lower expression of the plastid-encoded photosynthesis genes already in the dark and during the first hours of light exposure indicating that PEP activity is required for basal expression of plastid-encoded photosynthesis genes in the dark and during early light response. Furthermore, in etioplasts and proplastids a fully assembled PEP complex was revealed on Blue Native PAGE. Our results indicate that a full assembly of the PEP complex is possible in the dark and that PEP drives basal transcriptional activity of plastid-encoded photosynthesis genes in the dark. Assembly of the complex is most likely not a rate-limiting step for full activation of plastid-encoded photosynthesis gene expression which is rather achieved either by the abundance of the PEP complex or by some posttranslational regulation of the individual PEP components.
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| 11. |
- Ji, Yan, 1987-
(författare)
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Regulation of chloroplast development during the greening process
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Upon light exposure, the expression of one-third of the nuclear-encoded genes is changing, including genes encoding many chloroplast-targeted proteins responsible for the initiation of plastid transcription and the establishment of photosynthesis. The control of the nuclear-encoded genes involved in the development of chloroplast is referred to as anterograde signalling. In my thesis work I have focused on both cryptochrome and phytochrome signalling pathways regulating the transcription of photosynthesis-related genes during chloroplast development. The results in the thesis demonstrate that several light-responsive nuclear transcription factors play a direct role in chloroplast development, and reveal the regulatory mechanism underlying the initiation of plastid photosynthetic gene expression. In this thesis, bZIP16 was found as a CRY1 interacting factor. Together with bZIP68 and GBF1, they regulate the expression of LHCBs and SIG5 through a blue light signalling pathway, promoting cotyledon opening and chloroplast development during de-etiolation. These findings provide novel insights into the role of bZIP transcription factors during chloroplast development with the involvement of the cryptochrome signalling pathway. To further investigate how the plastid photosynthetic gene expression is initiated, I focused on the role of two plastid RNA polymerases, nuclear-encoded plastid RNA polymerase (NEP) and plastid-encoded plastid RNA polymerase (PEP). By combining the PIF3-binding motif analysis, mathematic modelling and photoreceptor mutant analysis, we demonstrated a PHYB-PIF3 mediated regulation of the initial expression of the nuclear-encoded PEP components, SIGs and PAPs with the G-box/PBE-box as potential PIF3 binding-site. I have also demonstrated the presence of a fully assembled PEP complex in both proplastids and etioplasts using 2D BN/SDS-PAGE and its importance for the basal level of psaA and psbA transcription in darkness and during the early light response.
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| 12. |
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| 13. |
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| 14. |
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| 15. |
- Kleine, Tatjana, et al.
(författare)
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Genome-wide gene expression analysis reveals a critical role for CRYPTOCHROME1 in the response of Arabidopsis to high irradiance
- 2007
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 144:3, s. 1391-406
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Tidskriftsartikel (refereegranskat)abstract
- Exposure to high irradiance results in dramatic changes in nuclear gene expression in plants. However, little is known about the mechanisms by which changes in irradiance are sensed and how the information is transduced to the nucleus to initiate the genetic response. To investigate whether the photoreceptors are involved in the response to high irradiance, we analyzed expression of EARLY LIGHT-INDUCIBLE PROTEIN1 (ELIP1), ELIP2, ASCORBATE PEROXIDASE2 (APX2), and LIGHT-HARVESTING CHLOROPHYLL A/B-BINDING PROTEIN2.4 (LHCB2.4) in the phytochrome A (phyA), phyB, cryptochrome1 (cry1), and cry2 photoreceptor mutants and long hypocotyl5 (hy5) and HY5 homolog (hyh) transcription factor mutants. Following exposure to high intensity white light for 3 h (1,000 µmol quanta m–2 s–1) expression of ELIP1/2 and APX2 was strongly induced and LHCB2.4 expression repressed in wild type. The cry1 and hy5 mutants showed specific misregulation of ELIP1/2, and we show that the induction of ELIP1/2 expression is mediated via CRY1 in a blue light intensity-dependent manner. Furthermore, using the Affymetrix Arabidopsis (Arabidopsis thaliana) 24 K Gene-Chip, we showed that 77 of the high light-responsive genes are regulated via CRY1, and 26 of those genes were also HY5 dependent. As a consequence of the misregulation of these genes, the cry1 mutant displayed a high irradiance-sensitive phenotype with significant photoinactivation of photosystem II, indicated by reduced maximal fluorescence ratio. Thus, we describe a novel function of CRY1 in mediating plant responses to high irradiances that is essential to the induction of photoprotective mechanisms. This indicates that high irradiance can be sensed in a chloroplast-independent manner by a cytosolic/nucleic component.
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| 16. |
- Norén Lindbäck, Louise, et al.
(författare)
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An interplay between bZIP16, bZIP68, and GBF1 regulates nuclear photosynthetic genes during photomorphogenesis in Arabidopsis
- 2023
-
Ingår i: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 240:3, s. 1082-1096
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Tidskriftsartikel (refereegranskat)abstract
- The development of a seedling into a photosynthetically active plant is a crucial process. Despite its importance, we do not fully understand the regulatory mechanisms behind the establishment of functional chloroplasts. We herein provide new insight into the early light response by identifying the function of three basic region/leucine zipper (bZIP) transcription factors: bZIP16, bZIP68, and GBF1. These proteins are involved in the regulation of key components required for the establishment of photosynthetically active chloroplasts. The activity of these bZIPs is dependent on the redox status of a conserved cysteine residue, which provides a mechanism to finetune light-responsive gene expression. The blue light cryptochrome (CRY) photoreceptors provide one of the major light-signaling pathways, and bZIP target genes overlap with one-third of CRY-regulated genes with an enrichment for photosynthesis/chloroplast-associated genes. bZIP16, bZIP68, and GBF1 were demonstrated as novel interaction partners of CRY1. The interaction between CRY1 and bZIP16 was stimulated by blue light. Furthermore, we demonstrate a genetic link between the bZIP proteins and cryptochromes as the cry1cry2 mutant is epistatic to the cry1cry2bzip16bzip68gbf1 mutant. bZIP16, bZIP68, and GBF1 regulate a subset of photosynthesis associated genes in response to blue light critical for a proper greening process in Arabidopsis.
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| 17. |
- Piñas Fernández, Aurora, et al.
(författare)
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Retrograde signaling and plant stress : plastid signals initiate cellular stress responses
- 2008
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Ingår i: Current opinion in plant biology. - : Current Biology. - 1369-5266 .- 1879-0356. ; 11:5, s. 509-513
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Tidskriftsartikel (refereegranskat)abstract
- Retrograde signaling coordinates the expression of nuclear genes encoding organellar proteins with the metabolic and developmental state of the organelle. These plastid signals are essential not only for coordinating photosynthetic gene expression in both the nucleus and in the chloroplasts but also for mediating plant stress responses. The chloroplasts therefore act as sensors of environmental changes and complex networks of plastid signals coordinate cellular activities and assist the cell during plant stress responses. Recent work suggests that information from both cytosolic-signaling and plastid-signaling networks must be integrated for the plant cell to respond optimally to environmental stress.
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| 18. |
- Routier, Cyril, et al.
(författare)
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Chitosan-modified polyethyleneimine nanoparticles for enhancing the carboxylation reaction and plants' CO2 uptake
- 2023
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 17:4, s. 3430-3441
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Tidskriftsartikel (refereegranskat)abstract
- Increasing plants' photosynthetic efficiency is a major challenge that must be addressed in order to cover the food demands of the growing population in the changing climate. Photosynthesis is greatly limited at the initial carboxylation reaction, where CO2 is converted to the organic acid 3-PGA, catalyzed by the RuBisCO enzyme. RuBisCO has poor affinity for CO2, but also the CO2 concentration at the RuBisCO site is limited by the diffusion of atmospheric CO2 through the various leaf compartments to the reaction site. Beyond genetic engineering, nanotechnology can offer a materials-based approach for enhancing photosynthesis, and yet, it has mostly been explored for the light-dependent reactions. In this work, we developed polyethyleneimine-based nanoparticles for enhancing the carboxylation reaction. We demonstrate that the nanoparticles can capture CO2 in the form of bicarbonate and increase the CO2 that reacts with the RuBisCO enzyme, enhancing the 3-PGA production in in vitro assays by 20%. The nanoparticles can be introduced to the plant via leaf infiltration and, because of the functionalization with chitosan oligomers, they do not induce any toxic effect to the plant. In the leaves, the nanoparticles localize in the apoplastic space but also spontaneously reach the chloroplasts where photosynthetic activity takes place. Their CO2 loading-dependent fluorescence verifies that, in vivo, they maintain their ability to capture CO2 and can be therefore reloaded with atmospheric CO2 while in planta. Our results contribute to the development of a nanomaterials-based CO2-concentrating mechanism in plants that can potentially increase photosynthetic efficiency and overall plants' CO2 storage.
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| 19. |
- Strand, Åsa, 1977-, et al.
(författare)
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Acclimation of Arabidopsis leaves developing at low temperatures. Increasing cytoplasmic volume accompanies increased activities of enzymes in the Calvin cycle and in the sucrose-biosynthesis pathway
- 1999
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Ingår i: Plant Physiology. - 0032-0889 .- 1532-2548. ; 119:4, s. 1387-1397
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Tidskriftsartikel (refereegranskat)abstract
- Photosynthetic and metabolic acclimation to low growth temperatures were studied in Arabidopsis (Heynh.). Plants were grown at 23 degrees C and then shifted to 5 degrees C. We compared the leaves shifted to 5 degrees C for 10 d and the new leaves developed at 5 degrees C with the control leaves on plants that had been left at 23 degrees C. Leaf development at 5 degrees C resulted in the recovery of photosynthesis to rates comparable with those achieved by control leaves at 23 degrees C. There was a shift in the partitioning of carbon from starch and toward sucrose (Suc) in leaves that developed at 5 degrees C. The recovery of photosynthetic capacity and the redirection of carbon to Suc in these leaves were associated with coordinated increases in the activity of several Calvin-cycle enzymes, even larger increases in the activity of key enzymes for Suc biosynthesis, and an increase in the phosphate available for metabolism. Development of leaves at 5 degrees C also led to an increase in cytoplasmic volume and a decrease in vacuolar volume, which may provide an important mechanism for increasing the enzymes and metabolites in cold-acclimated leaves. Understanding the mechanisms underlying such structural changes during leaf development in the cold could result in novel approaches to increasing plant yield.
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| 20. |
- Strand, Åsa, 1977-, et al.
(författare)
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Altering flux through the sucrose biosynthesis pathway in transgenic Arabidopsis thaliana modifies photosynthetic acclimation at low temperatures and the development of freezing tolerance
- 2003
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Ingår i: Plant, Cell and Environment. - 0140-7791 .- 1365-3040. ; 26:4, s. 523-535
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Tidskriftsartikel (refereegranskat)abstract
- To test the hypothesis that the up-regulation of sucrose biosynthesis during cold acclimation is essential for the development of freezing tolerance, the acclimation responses of wild-type (WT) Arabidopsis thaliana (Heynh.) were compared with transgenic plants over-expressing sucrose phosphate synthase (over-sps) or with antisense repression of either cytosolic fructose-1,6-bisphosphatase (antifbp) or sucrose phosphate synthase (antisps). Plants were grown at 23 degreesC and then shifted to 5 degreesC. The leaves shifted to 5 degreesC for 10 d and the new leaves that developed at 5 degreesC were compared with control leaves on plants at 23 degreesC. Plants over-expressing sucrose phosphate synthase showed improved photosynthesis and increased flux of fixed carbon into sucrose when shifted to 5 degreesC, whereas both antisense lines showed reduced flux into soluble sugars relative to WT. The improved photosynthetic performance by the over-sps plants shifted to 5 degreesC was associated with an increase in freezing tolerance relative to WT (-9.1 and -7.2 degreesC, respectively). In contrast, both antisense lines showed impaired development of freezing tolerance (- 5.2 and -5.8 degreesC for antifbp and antisps, respectively) when shifted to 5 degreesC. In the new leaves developed at 5 degreesC the recovery of photosynthesis as typically seen in WT was strongly inhibited in both antisense lines and this inhibition was associated with a further failure of both antisense lines to cold acclimate. Thus, functional sucrose biosynthesis at low temperature in the over-sps plants reduced the inhibition of photosynthesis, maintained the mobilization of carbohydrates from source leaves to sinks and increased the rate at which freezing tolerance developed. Modification of sucrose metabolism therefore represents an additional approach that will have benefits both for the development of freezing tolerance and over-wintering, and for the supply of exportable carbohydrate to support growth at low temperatures.
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| 21. |
- Strand, Åsa, 1977-, et al.
(författare)
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Decreased expression of two key enzymes in the sucrose biosynthesis pathway, cytosolic fructose-1,6-bisphosphatase and sucrose phosphate synthase, has remarkably different consequences for photosynthetic carbon metabolism in transgenic Arabidopsis thaliana
- 2000
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Ingår i: The Plant Journal. - 0960-7412 .- 1365-313X. ; 23:6, s. 759-770
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Tidskriftsartikel (refereegranskat)abstract
- Photosynthetic carbon metabolism was investigated in antisense Arabidopsis lines with decreased expression of sucrose phosphate synthase (SPS) and cytosolic fructose-1,6-bisphosphatase (cFBPase). In the light, triose phosphates are exported from the chloroplast and converted to sucrose via cFBPase and SPS. At night, starch is degraded to glucose, exported and converted to sucrose via SPS, cFBPase therefore lies upstream and SPS downstream of the point at which the pathways for sucrose synthesis in the day and night converge, Decreased cFBPase expression led to inhibition of sucrose synthesis; accumulation of phosphorylated intermediates; Pi-limitation of photosynthesis; and stimulation of starch synthesis. The starch was degraded to maintain higher levels of sugars and a higher rate of sucrose export during the night. This resembles the response in other species when expression of enzymes in the upper part of the sucrose biosynthesis pathway is reduced. Decreased expression of SPS inhibited sucrose synthesis, but phosphorylated intermediates did not accumulate and carbon partitioning was not redirected towards starch. Sugar levels and sucrose export was decreased during the night as well as during the day. Although ribulose-1,5-bisphosphate regeneration and photosynthesis were inhibited, the PGA/triose-P ratio remained low and the ATP/ADP ratio high, showing that photosynthesis was not limited by the rate at which Pi was recycled during end-product synthesis. Two novel responses counteracted the decrease in SPS expression and explain why phosphorylated intermediates did not accumulate, and why allocation was not altered in the antisense SPS lines. Firstly, a threefold decrease of PPI and a shift of the UDP-glucose/hexose phosphate ratio favoured sucrose synthesis and prevented the accumulation of phosphorylated intermediates. Secondly, there was no increase of AGPase activity relative to cFBPase activity, which would prevent a shift in carbon allocation towards starch synthesis. These responses are presumably triggered when sucrose synthesis is decreased in the night, as well as by day.
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| 22. |
- Strand, Åsa, 1977-, et al.
(författare)
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Development of Arabidopsis thaliana leaves at low temperatures releases the suppression of photosynthesis and photosynthetic gene expression despite the accumulation of soluble carbohydrates
- 1997
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Ingår i: The Plant Journal. - 0960-7412 .- 1365-313X. ; 12:3, s. 605-614
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Tidskriftsartikel (refereegranskat)abstract
- Arabidopsis thaliana plants were grown at 23 degrees C end changes in carbohydrate metabolism, photosynthesis and photosynthetic gene expression were studied after the plants were shifted to 5 degrees C. The responses of leaves shifted to 5 degrees C after development at 23 degrees C are compared to leaves that developed at 5 degrees C. Shifting warm developed leaves to 5 degrees C lead to a severe suppression of photosynthesis that correlated with a rapid and sustained accumulation of hexose phosphates and soluble sugars. Associated with the suppression of photosynthesis and the accumulation of soluble sugars was a reduction in the amount of transcript for genes encoding photosynthetic proteins (cab and rbcS). In contrast, leaves that developed at 5 degrees C showed an increase in photosynthesis and control levels of photosynthetic gene expression. This recovery occurred even though leaves that developed at 5 degrees C maintained large pools of soluble sugars. Leaves that developed at 5 degrees C also showed a strong upregulation of the cytosolic pathway for soluble sugar synthesis but not of the chloroplastic pathway for starch synthesis. This was shown at the level of both enzyme activity and the amount of transcript. Thus, development of Arabidopsis leaves at 5 degrees C resulted in metabolic changes that enabled them to produce and accumulate large soluble sugar pools without any associated suppression of photosynthesis or photosynthetic gene expression. These changes were also associated with enhanced freezing tolerance. We suggest that this reprogramming of carbohydrate metabolism associated with development at tow temperature is essential to the development of full freezing tolerance and for winter survival of over-wintering herbaceous annuals.
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| 23. |
- Wallentin, Åsa, et al.
(författare)
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Psychiatrists’ Experience of Vocational Rehabilitation for Patients with Mental Illness
- 2021
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Ingår i: Psychiatric quarterly. - : Springer Science and Business Media LLC. - 0033-2720 .- 1573-6709. ; 92, s. 1217-1229
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to explore psychiatrists’ experience of vocational rehabilitation for patients with mental illness. The study employed a qualitative design to explore psychiatrists’ experience of vocational rehabilitation. Ten psychiatrists, five women and five men, 33–62 years of age (median 40), were interviewed. All of them worked with patients at Sahlgrenska University Hospital. The interviews were analyzed using inductive thematic analysis. All participants considered vocational rehabilitation to be of great importance for patients’ well-being and health. The results were characterized by two opposite experiences: frustration and agency, these were the two main themes in the analysis. All narratives embraced both experiences, but some reflected more frustration and others more agency. In order for the psychiatrist to master the assignment, there is a need for further training and supervision. The psychiatrist’s role, as well as other professional roles within the team, requires clarification, and the support from rehabilitation coordinators and occupational therapists should be enhanced. There is a need for improved cooperation with external actors.
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| 24. |
- Yang, Qi, et al.
(författare)
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Two dominant boreal conifers use contrasting mechanisms to reactivate photosynthesis in the spring
- 2020
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Boreal forests are dominated by evergreen conifers that show strongly regulated seasonal photosynthetic activity. Understanding the mechanisms behind seasonal modulation of photosynthesis is crucial for predicting how these forests will respond to changes in seasonal patterns and how this will affect their role in the terrestrial carbon cycle. We demonstrate that the two co-occurring dominant boreal conifers, Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies), use contrasting mechanisms to reactivate photosynthesis in the spring. Scots pine downregulates its capacity for CO2 assimilation during winter and activates alternative electron sinks through accumulation of PGR5 and PGRL1 during early spring until the capacity for CO2 assimilation is recovered. In contrast, Norway spruce lacks this ability to actively switch between different electron sinks over the year and as a consequence suffers severe photooxidative damage during the critical spring period.
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