NEWS FROM
PHYSIOLOGIA PLANTARUM
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Published monthly on behalf of SPPS by Wiley-Blackwell.
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Mycorrhizal fungi make host cleave sugar
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Arbuscular mycorrhizal fungi are deficient in carbon acquisition capabilities and completely depend on the roots of a host plant for carbon supply. It has been assumed that sucrose is hydrolyzed by cell wall invertases at the plant-fungus interface, and that the resulting hexoses are subsequently taken up by the fungus. The involvement of such a cell wall invertase has, however, not previously been shown, but now Spanish scientists from Granada have provided the evidence. They show that both cell wall and vacuolar invertases are upregulated in infected tomato roots, and that this is a direct consequence of fungal infection.
Read full article free: Garcia-Rodriguez et al (April 2007) Physiologia Plantarum 12: 737-746
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NEWS IN BRIEF
FROM OTHER JOURNALS
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Genetic diet causes slim endodermis
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Source: Cui et al (20 April 2007) Science 316: 421-425
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Quantum tricks in photosynthesis
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Source: Engel et al (12 April 2007) Nature 446: 782-786
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Scandinavian research institute:
Laboratory of Plant Physiology and Molecular Biology, Turku, Finland
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Laboratory of Plant Physiology and Molecular Biology is situated in Turku, Finland. From vanha.sci.utu.fi/kasvimb/ukhome.html
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If you ever go visit someone in outer space, remember to stop by at Turku and pick up some flowers or other photosynthetic organisms. One of the many aspects of plant biology they study is namely the suitability of higher plants and microalgae for use as biological life support systems under the harsh conditions on Mars or other distant destinations in space.
And though outer space is not the laboratory's favorite experimental playground, their research is focused on how environmental conditions affect the life processes of plants and cyanobacteria. Photosynthesis - and in particular the dynamics of photosystem II - is a key aspect where cyanobacteria are studied in parallel with Arabidopsis, and to complete the list of experimental organisms, the laboratory also utilizes fungi and plant viruses in their research.
The Laboratory of Plant Physiology and Molecular Biology is headed by Professor Eevi Rintamäki and employs approximately 25 scientists, 16 PhD students, 5 technicians and a crowd of students. The laboratory is part of the Department of Biology at University of Turku, and is located in modern facilities both at the department and at the multidisciplinary BioCity in the historical center of the town.
Research at the Laboratory is divided into eight groups:
Eva-Mari Aro: Photosynthetic membrane complexesPaula Mulo: Signalling mechanisms in photosynthesisEevi Rintamäki: Chloroplast redox reactionsEsa Tyystjärvi: Plant Biophysics ProjectTaina Tyystjärvi: Gene expression in cyanobacteriaPirkko Mäenpää: Protein analysis in cyanobacteriaKirsi Lehto: Plant virus projectsTapani Yli-Mattila: Plant-fungus interactionsMarjatta Raudaskoski: Small Rho GTPases in fungi
The first four groups are centered around photosynthesis, whereas the remaining four groups are looking into other aspects of organisms like cyanobacteria, fungi and viruses.
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The biochemistry of solar powered hydrogen production. Courtesy of Eva-Mari Aro.
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Eva-Mari Aro is one of the driving forces at the laboratory and her group was recently awarded with the national Centre of Excellence status from the Academy of Finland where she also holds an Academy Professorship. The work will aim at advancing the knowledge of biosynthetic and signalling pathways of photosynthesis at the level of systems biology. Arabidopsis and cyanobacteria will be subject to genomic, proteomic and metabolomic analysis (read about 'omics' in a former article in SPPS Newsletter) and emphasis will be put on the interaction and modification of proteins.
Another aspect covered by the Centre is biohydrogen production by photosynthetic microorganisms. Coined as 'solar fuel' this renewable energy source has a huge potential, and Eva-Mari Aro's group will initiate a systematic development of methods to improve its production in cyanobacteria. The Centre - which also includes University of Helsinki - runs for a 6 year period starting in 2008 and has been granted over 2 mio. € during the first 3 years.
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The structural model of the Arabidopsis ferredoxin-NADP+-oxidoreductase made it to the cover of the Plant Journal.
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Eva-Mari Aro is also interested in how the chloroplast participates in adaptation to environmental stress. Besides from capturing light energy and generating ATP and reductants for carbon dioxide fixation, the chloroplast redox reactions also function to regulate both nuclear and chloroplast gene expression in a way that allows the plant to initiate an adaptive response. In collaboration with Paula Mulo (who led the study), Eevi Rintamäki and other colleagues at the Turku laboratory it was very recently shown how the chloroplast-targeted enzyme ferredoxin-NADP+-oxidoreductase (FNR) contribute to this process.
The team used knock-out mutants in Arabidopsis to characterize the structure and function of the enzyme. The enzyme exists in two isoforms and structural modelling suggested that they are capable of forming both hetero- and homodimers. Apparently, the heterodimer is essential for attachment of the enzyme to the thylakoid membrane, whereas the homodimer seems to regulate how electrons are distributed between the cyclic and linear electron transfer pathway according to environmental cues.
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The STN7 kinase controls the energy balance between Photosystem I and II. From www.molbio.unige.ch/rochaix/index.php
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Another way for plants to adopt to changes in light quality and quantity has been studied by Eva-Mari Aro in collaboration with Paula Mulo. The STN7 kinase is known to balance energy input and consumption between Photosystem I and II by phosphorylation of proteins in the light harvesting complex, causing its displacement within the thylakoid membrane. The team studied Arabidopsis plants mutated in the stn7 gene and found that the kinase is required to maintain a buffering system, which allows the plants to acclimate to fluctuating light conditions.
Acclimation of photosynthesis to changing growth conditions is also the main topic the two groups led by Esa Tyystjärvi and Taina Tyystjärvi, respectively. The former focuses on photoinhibition and suggests that it is triggered when a manganese ion in the oxygen-evolving complex are exited by light and looses its binding. This renders the complex inactive and leads to irreversible damage of the Photosystem II reaction centre. Evidence supporting this so-called 'manganese mechanism' has recently been published by the two groups using a range of experimental organisms covering E. coli to pumpkin.
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Regulation of gene expression is studied in the cyanobacteria Synechocystis. From www-cyanosite.bio.purdue.edu/images/images.html
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The model organism of choice for Taina's group is, however, cyanobacteria and she studies how the RNA polymerase holoenzyme is involved in regulation of gene expression. Cyanobacteria, specifically Synechocystis, is also studied by the group of Pirkko Mäenpää. She is looking into how proteins are involved in stress adoptation. In a recent comparative proteomic analysis she identified proteins that were specifically expressed during acid stress.
Surprisingly, only few proteins from the cytoplasmic fraction were induced by acidity, and these did not include general stress proteins like HSP's and chaperones. On the contrary, several proteins from the periplasm, i.e. the space between the plasma membrane and the outer membrane, were differentially expressed at acidity or alkalinity. Many of these proteins were previously unknown and in total Pirkko Mäenpää and her colleagues identified 14 novel proteins from the periplasmic space of the cyanobacteria.
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Black currant reversion nepovirus causes reversion disease in blackcurrant. From www.ars-grin.gov/cor/ribes/ribsymp/reversion2.html
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Among the other organisms under investigation in Turku are fungi and viruses. Kirsi Lehto is - apart from having an interest in astrobiology and the molecular evolution of proteins - leading the virus project. The main project concerns characterization of regulatory elements and proteolytic cleavage sites of the black currant reversion nepovirus. In a very recent publication, she showed that the 5' non-translated region of RNA2 is a translational enhancer by fusing the element to a reporter gene and expressing the construct in tobacco protoplasts.
Tapani Yli-Mattila is working with several aspects of Fusarium and other fungi, and is the Finnish coordinator of the Nordic network project 'New emerging mycotoxins and other metabolites in toxigenic fungi of Northern Europe'. One of his interests is to develop methods for PCR-based detection of toxic fungi. Cereals are commonly infected by mould species that can produce a range of mycotoxins and lead to contamination of foods and feed, and it is a challenge to design PCR primers that can detect a broad range of fungal strains.
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Fruitbodies of GTPase-mutants (C-F) don't develop properly. From Schubert et al (2006) Eucaryotic Cell 5: 683-695.
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Another line of fungal research is carried out by Marjatta Raudaskoski who studies the role of GTPases in the wood-decaying fungus Schizophyllum. In collaboration with German scientists, she recently showed that the a GTPase-activating protein, Gap1, is required for sexual development and hyphal growth orientation. Mutants lacking the functional protein developed abnormal gills and produced no sperm, and their hyphae did not show oriented growth and were unable to form clamp connections, i.e. the process that ensures each cell is binucleate.
You can find more information about plant science in Turku at the laboratory's official website.
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