Archiv der bisher stattgefundenen Seminare

Ort: Box

Remko Offringa - A suppressor of meristem maturation promotes longevity in flowering plants

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Adriano Nunes-Nesi - The importance of nicotinamide adenine dinucleotide transport in Arabidopsis thaliana

September 2018
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Elena Baena-Gonzalez - How do plants manage their energy?

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Sandra Kerbler - Unravelling the mitochondrial electron transport chain in the cold: is ATP synthase the key?

  • Datum: 17.03.2017
  • Uhrzeit: 14:00 - 15:30
  • Vortragende(r): Sandra Kerbler
  • PLANT ENERGY BIOLOGY UNIVERSITY OF WESTERN AUSTRALIA, Perth, Australia
  • Ort: Box
  • Raum: 0.21
  • Gastgeber: Mark Stitt
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Cecilia Emanuelsson - The chloroplast-localized Hsp21 – structure and interactions

  • Datum: 21.02.2017
  • Uhrzeit: 14:00 - 15:30
  • Vortragende(r): Cecilia Emanuelsson
  • Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University, Sweden
  • Ort: Box
  • Raum: 1.12
  • Gastgeber: Salma Balazadeh
The small heat shock protein (sHsp) chaperones can prevent aggregation of other proteins. sHsps may be among the most highly upregulated proteins in heat-stressed cells and in plants the sHsps confer an especially pronounced and important part of the stress response. The sHsps rapidly sequester destabilized client proteins, thereby overcoming the kinetic competition with aggregation. The sHsps typically act on early unfolding intermediates and capture unfolded conformations present for only a small fraction of the time. There are three structurally and functionally distinct regions in sHsps: the α-crystallin domain (ACD) that defines the family of sHsps, the C-terminal region (CTR), with a conserved I/V-X-I/V motif and the N-terminal region (NTR), which differs in length and composition between the different sHsps. The chloroplast-localized sHsp, referred to as Hsp21, evolved when the land-plants developed in response to the selection pressure in a non-water environment. In Hsp21 the NTR contains a unique set of methionines in an amphipathic α-helix-motif. Hsp21 plays a crucial role in resistance to heat and oxidative stress in Arabidopsis thaliana, during which the Hsp21 dodecamer undergoes a conformational change coupled to methionine oxidation. Some Hsp21 may also translocate into the thylakoid membranes during plant heat stress. We have recently obtained a structural model of Hsp21, suggesting that the CTR stabilizes the dodecamer while the NTR can interact with client proteins on the outside of the dodecamer, and we have developed an approach with crosslinking mass spectrometry to investigate the interactions between Hsp21 and client proteins. [mehr]

Sandra Schmoeckel - The genome of Chenopodium quinoa provides insights into saponin biosynthesis

Chenopodium quinoa (quinoa) is a highly nutritious grain crop with high abiotic stress tolerance that has been identified as an important crop to improve world food security; unfortunately, few resources are available to facilitate its genetic improvement. Here we report the assembly of a high-quality, chromosome-scale reference genome sequence for quinoa, which was produced using single-molecule real-time sequencing in combination with optical, chromosome contact, and genetic maps. We also report reduced-coverage genome sequences for 22 other accessions of the allotetraploid goosefoot complex and two diploids from among quinoa’s ancestral gene pools. The genome sequence facilitated the identification of the transcription factor likely to control the production of anti-nutritional triterpenoid saponins found in quinoa seeds, including a mutation that appears to cause alternative splicing and the inclusion of a premature stop codon, thereby inactivating the protein and leading to the absence of saponins in sweet quinoa accessions. These genomic resources are an important first step towards the genetic improvement of quinoa to help increase global food security in the face of climate change and a growing world population. [mehr]

Lukas M. Müller - The sucrose storage metabolism regulates carbohydrate supply for growth by a concentration-dependent kinetics but not the circadian clock in barley

  • Datum: 28.10.2016
  • Uhrzeit: 10:45 - 12:15
  • Vortragende(r): Lukas M. Müller
  • Institute of Plant Genetics, Heinrich Heine University, Düsseldorf & Max Planck Institute for Plant Breeding Research, Department of Plant Developmental Biology, Cologne, Germany
  • Ort: Box
  • Raum: 0.21
  • Gastgeber: Mark Stitt
The circadian clock controlscarbohydrate metabolism and growth in Arabidopsis, suggesting it as key targetfor crop improvement. However, my recent work shows that the circadian clockthrough EARLY FLOWERING 3 (ELF3) does not determine carbohydrate supply forgrowth in barley at night, in contrast to Arabidopsis. I find that carbohydratesupply from the leaves at night is dominated by sucrose in barley but notstarch as in Arabidopsis. Depletion of transitory sucrose from the leaf wasexponential and almost exhausted at the end of the night, even under unexpectedextension of photoperiod. This depletion pattern depended on the sucrosecontent at the end of the day, was independent from circadian control andpresumably determined by SUCROSE TRANSPORTER 2 (SUT2) through catalyzingsucrose export from the vacuole by a kinetics of first order. On the otherhand, degradation of the little amounts of transitory starch in barley wastemporally controlled by the clock component ELF3 in both barley and Arabidopsis.Therefore, barley and Arabidopsis apply two different forms of nocturnalcarbohydrate supply: The sucrose storage and the starch storage metabolism.Consistent with regulation by a clock-driven program or a transporter-catalyzedkinetic, carbohydrate supply from starch was compensated against lowtemperature while reduced for sucrose so that barley, but not Arabidopsis,reduced biomass after growth in cool nights. Growth of wheat, rice and wildbarley but not Brachypodium also depended on the sucrose storage metabolism. Insummary, my findings explain how cool nights and the circadian clock determinegrowth in different species despite the conservation of the circadian clock. [mehr]

Ilka Axmann - Career Talk: Daily life of cyanobacteria  and their researcher

Cellularclocks allow organisms to anticipate the environmental cycles of day and nightby synchronizing their internal, circadian rhythms with the rising and settingof the sun. In cyanobacteria the clockconsists of solely three proteins - KaiA, KaiB and KaiC - orchestrating geneexpression. Complex formation between Kai proteins and, therefore, theirstoichiometry is essential in maintaining robust circadian oscillations. Thus,it is puzzling that several cyanobacteria, e.g. Synechocystis, contain multiple kai-genecopies. Our global transcriptomicanalyses of light-dark synchronised Synechocystis cultures indicate arather light-driven than a circadian regulated pattern in global geneexpression. We detected several small RNAs encoded at the kai gene locibut antisense to kai genes whichmight be involved or even interfere with circadian regulation. Besides severalother studies, we have already shown how small RNAs can influence the temporalregulation of gene expression. Thus, regulation by antisense RNA might be afundamental mechanism for the daily coordination in cyanobacteria.Althoughthe expression of many gene transcripts fluctuates over day and night, thesewere less pronounced at the protein level. Therefore, abundance and constituencywere probed of protein complexes present in cyanobacteria using size exclusionchromatography-based proteomics. Following complexes such as the RNApolymerase, the ribosome and complexes involved in photosynthesis, we observethat these complexes change not only in abundance but also in constituency,with associated proteins being either present or absent. We conclude that thedynamic assembly of protein complexes is also a key-player in the processesgoverning the daily rhythm. Why I decided and how Imanage being a female researcher and mother of two children while researchingon regulatory RNAs and circadian clock for about 15 years now, I am going torecapitulate. [mehr]

Helmut Kirchhoff - From Molecules to Membranes: Design Principles of Photosynthetic Membranes

More than a billion years of evolution shaped and tuned the photosynthetic apparatus harbored in thylakoid membranes to make energy conversion both efficient and robust in an often-unpredictable ever-changing nature. This success story of biological energy conversion is based on built-in structural flexibilities of the photosynthetic machinery that allows for a dynamic response on environmental cues. These structural alterations of the thylakoid membrane network occur on three different length scales ranging from the molecular level (Å - few 10 nm), the meosocopic level (several 10 nm – several 100 nm), to the overall membrane level (m). Classification into these three structural levels turned out to be extremely helpful since different physicochemical principles are realized at different length scales which require different methodical approaches to study them. The talk surveys examples for structural alterations on all three levels. In detail, for the molecular level, data on lipid-protein interactions will be presented that show the impact of highly abundant non-bilayer lipids for the structure and function of light-harvesting protein complexes. For the mesoscopic level, the significance of a supra-molecular protein reorganization from disordered to highly ordered semicrystalline arrays will be unraveled. Finally, it will be demonstrated that dynamic swelling and shrinkage of the entire membrane system is a crucial structural alteration for the control of diffusion-dependent electron transport and protein repair processes. Unraveling the design principals for the three structural levels and their interdependency is indispensible for a holistic understanding and modeling of photosynthetic energy conversion. [mehr]

Assaf Vardi - The “virocell” metabolism – Metabolic innovations during host-virus interactions in the ocean

Marine viruses that infect marine microorganisms are recognized as major ecological and evolutionary driving forces, shaping community structure and nutrient and energy cycling in the marine environment. Nevertheless, the cellular mechanisms that govern these host-virus dynamics are largely underexplored. Recent reports highlighted a novel genomic inventory found in marine viruses which can encode auxiliary metabolic genes previously thought to be restricted to their host genomes. Thus, these genes can expand viral metabolic capabilities and energy transfer between host cells and their environment. A major challenge in our current understanding of host-virus interactions in the marine environment is to decode the wealth of genomic and metagenomic data and translate it into cellular mechanisms that mediate host susceptibility and resistance to viral infection. Emiliania huxleyi is a globally important coccolithophore forming massive algal blooms in the North Atlantic Ocean that are routinely infected and terminated by large DNA viruses, coccolithoviruses (EhVs). We explore the molecular and metabolic basis for these host-virus dynamics and the signal transduction pathways that mediate host-virus interactions. By combining genome-enabled technologies and analytical chemistry approaches, we were able to identify several fundamental metabolic pathways that mediate these host-virus interactions. We revealed the role of viral-encoded sphingolipid, redox and DMS metabolism and their function in determining host cell fate (e.g. PCD and autophagy) and viral replication strategies. We currently examine the transcriptomic remodeling of host-virus interactions at a single cell resolution in order to provide novel insights into the cellular mechanisms that govern the “arms race” of the virocell during algal blooms dynamics in the ocean. [mehr]

Dagmar Lyska - Beyond green – harvesting and dissipating light energy in the heterokont alga Nannochloropsis oceanica

Understanding the fundamental processes of photosynthesis and its regulation has become more and more important with growing energy and agricultural demands and the need to enhance feedstock performance and yields. Until recently, research on photosynthesis has been focused largely on cyanobacteria, green algae and land plants. However, heterokont microalgae, such as Nannochloropsis, are emerging as potential feedstocks for biofuels due to their high photoautotrophic biomass and lipid accumulation rates. The photosynthetic properties of Nannochloropsis are similar to, but also significantly different, from green algae, e.g. in terms of light harvesting or dissipation of excess light energy (Non-Photochemical Quenching, NPQ). We want to understand these mechanisms and their regulation in Nannochloropsis and therefore designed molecular tools for the genetic modification of this non-model organism. Using a non-lethal, easy-to-screen mutant phenotype, we have established protocols for targeted gene knockout by homologous recombination and by the CRISPR/Cas9 system for the Nannochloropsis oceanica strain CCMP1779. Furthermore, we have created a library of random insertional mutants with altered NPQ capacities and/ or kinetics and identified disrupted genes using PCR-based methods. Combining the forward and reverse genetics approaches with biochemical and spectroscopic analyses, we are now able to address the significance of the xanthophyll cycle-dependent vs. the LHCX(LHCSR)-dependent component of NPQ and the molecular basis of light harvesting in Nannochloropsis. [mehr]

Aude Coupel-Ledru

March 2016
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Independent evolution of miRNAs targeting orthologous genes – chance or necessity?

Independent evolution of miRNAs targeting orthologous genes – chance or necessity? LYDIA GRAMZOW, DAJANA LOBBES, GÜNTER THEIßEN Friedrich Schiller University Jena, Germany MicroRNAs (miRNAs) are small molecules that generally negatively regulate gene expression. They have been shown to have a faster birth and death rate than protein-coding genes. In plants, a famous hypothesis on how a miRNA can be born is the inverted duplication hypothesis, according to which a miRNA evolves by inverted duplication of its target gene. Here, we provide evidence for an origin by inverted duplication for the miRNAs miR444 and miR824. Using publicly available genome and transcriptome data, cloning strategies and detection of miRNAs by Northern blot hybridization, we elucidate that the miR444 originated early in the evolution of monocotyledonous plants while the miR824 evolved in Brassicaceae. For both miRNAs we show that, at least early in their evolution, these miRNAs and their target genes were in close proximity in the genome, indicating the origin by inverted duplication. Remarkably, both miRNAs target the same subfamily of MADS-box genes: AGL17-like genes encoding for transcription factors involved in root and shoot development. Only one out of more than a dozen other subfamilies of MADS-box genes in flowering plants is known to also be targeted by a miRNA. Hence, the question arises as to whether the regulation of AGL17-like genes by two different miRNAs in two different groups of flowering plants is more than chance. We will address this question in light of our current knowledge about AGL17-like genes. [mehr]

Structure and Dynamics of Intrinsically Disordered and Partially Folded Proteins in Solution

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The key evidence underlying the top-down construction, propagation, and analysis of genome-scale plant metabolic models

There is a growing demand for the effective metabolic and genetic manipulation of plants to benefit human society in many ways. The layers of complex interacting biological networks affecting plant growth makes this a difficult task, and several genome-scale metabolic reconstructions have been published as a means to enable researchers to explore these networks in silico. However the construction of these networks rely heavily on the evidence available for the biochemistry, gene-reaction associations, and compartmentalization. Furthermore propagating these networks for any species other than the model plant Arabidopsis thaliana in turn rely heavily on the phylogeny of plant protein families. I present the PlantSEED project where we set a gold standard for the curation of enzymes involved in plant primary metabolism, including isofunctional paralogs, from which we generate a draft top-down model of Arabidopsis thaliana and, via conservative use of EnsemblCompara families, 9 other species. I will also discuss the use of additional evidence to build a larger, compartmentalized model of Maize, and the use of transcript profiles to build. The data, along with additional functionality for metabolic flux analysis, is available in both the DOE Systems Biology Knowledgebase and our PlantSEED web portal. Finally I will describe our future plans for the expansion of PlantSEED. [mehr]

Executer: a protein family involved in singlet oxygen-mediated signaling in chloroplast

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Apocarotenoid biosynthesis in saffron stigmas: a tale of three compartments

July 2015
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Functional Characterisation of Plant-Specific Mitochondrial Outer Membrane Proteins in Arabidopsis thaliana

May 2015
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