Seminare

Seminare

Das Max-Planck-Institut für Molekulare Pflanzenphysiologie hat regelmäßig herausragende Forscher zu Gast, die Vorträge über ihre aktuellen Projekte halten und so den Austausch unter den Wissenschaftlern fördern.

Eine Übersicht über die kommenden Veranstaltungen finden Sie hier. Seminare finden für gewöhnlich Mittwochs in der Zeit von 14:00 Uhr bis 15:30 Uhr im Seminarraum im Zentralgebäude (1.052 und 1.053) statt, Abweichungen in Zeit und Ort sind jedoch möglich.

May 2016

Cheryl A. Kerfeld - Diversity, structure, function, assembly and engineering of bacterial microcompartments

Bacterial microcompartments are widespread metabolic modules found in at least 23 bacterial phyla. The carboxysome is the best studied bacterial microcompartment and serves to illustrate the basic principles of bacterial micrcompartment structure and function. It consists of a selectively permeable protein shell encapsulating ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and carbonic anhydrase. Cyanobacteria depend on the carboxysome to concentrate carbon dioxide near RuBisCO while minimizing the wasteful side reaction with oxygen. The carboxysome functions as an organelle but, in contrast to eukaryotic organelles, is composed entirely of protein; thousands of protein subunits self-assemble to form this ~300 MDa complex. Many bacteria assemble architecturally-related types of organelles for diverse catabolic functions. Our studies suggest that the principles of carboxysome structure, function and assembly likely extend to other bacterial microcompartments and provide the foundation for design and construction of synthetic nanoreactors based on bacterial microcompartment architecture. [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]

Maria Albani - Arabis alpina as a model to study flowering and perennial traits

A. alpina is a Brassicaceae species and perennial relative of the annual model Arabidopsis thaliana. Comparative studies between these two models have been successful in tracing at the molecular level the mechanisms that contributed to the diversification of the annual and perennial life strategies. Differences in flowering behavior between annual and perennial species contribute to differences in their life strategy. A text book example is the role of FLOWERING LOCUS (FLC) in life history evolution of A. alpina and A. thaliana. FLOWERING LOCUS C (FLC) is a key floral repressor in A. thaliana that regulates flowering in response to vernalisation. Its orthologue in A. alpina, PERPETUAL FLOWERING 1 (PEP1) also ensures flowering in response to vernalisation but in addition contributes to perennial traits such as polycarpic growth habit and the duration of the flowering episode. pep1 mutants flower without vernalisation and show reduced return to vegetative growth. My group is studying the regulation of inflorescence development and outgrowth in perennials using A. alpina as a model. We performed an enhancer screen of the pep1-1 mutant and isolated several second-site mutants that show inflorescence phenotypes. Mapping by sequencing of several mutants reveal a novel regulator not previously studied in A. thaliana. [mehr]

Akiko Satake - Phase response of plant circadian clocks leads to robust metabolic rhythms under seasonal variations in day length

Growth and maintenance processes requiring carbon must be maintained despite daily fluctuations in light and dark conditions. Buffering against daily fluctuations in the carbon supply is achieved through a diel turnover of starch. Starch accumulates in the day and decreases in the night with almost linearly. Moreover, starch accumulates rapidly and decreases slowly as night-period decreases, which allows plants to maintain the same amount of starch at the end of the night regardless of photoperiod. Recent studies reported the importance of feedbacks between circadian clocks and carbon metabolism for optimal growth. However how plants adjust starch metabolism in response to changing photoperiod remains elusive. To investigate the mechanism of flexible coordination of starch metabolism, we modeled the interplay of carbon metabolism and circadian clocks. We first showed that the linearity of starch metabolism is an emergent property of sucrose homeostasis. We next demonstrated that hyperbolic function of starch degradation rate that has a peak at dawn is necessary for sucrose homeostasis. We then showed that a phase response curve to sucrose signals that realizes sucrose homeostasis is the same as the one determined by the experiment, which shows phase advance in the morning and delay in the night. We finally showed that the phase response to sucrose signals leads to appropriate adjustment of starch accumulation and degradation rates. These results indicate that the responsiveness of plant circadian clocks to sucrose signals has the adaptive significance for optimal growth under diel and seasonal fluctuations in environments. [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]

Haim Treves - Chlorella ohadii - fastest growing, photodamage and desiccation tolerant alga from desert crusts

The unparalleled performance of Chlorella ohadii clearly indicated that we lack information on the photosynthetic machinery and what sets the upper growth limits. When grown under optimal laboratory or controlled outdoor conditions, this alga, recently isolated from one of the harshest environments (a biological desert sand crust), exhibits the fastest growth rates ever reported for an alga, division times shorter than 2 h were recorded. The cultures perform very high photosynthetic rates and reach high cell densities (1.3*109 cells/mL). Unlike other photosynthetic organisms, C. ohadii productivity is unaffected by irradiances twice full sun light; and the level of protein D1, encoded by a single gene, is hardly affected. Rather than succumbing to photodamage C. ohadii undergoes major structural and compositional changes (including 2-3 fold increase of the lipid and carbohydrate contents and a large rise in the abundance of the thylakoids), emphasizing the importance of its unique PSII functioning as well as highly efficient reductant utilization downstream of the photosynthetic reaction centers. Comparing its genome sequence with those of other algae shed light on the unique genetic potential of C. ohadii, its growth and photosynthetic performance and its ability to withstand salinity and desiccation in its natural environment. RNA-Seq revealed regulation of genes networks under changing light and trophic regimes, and provided novel insights on the mechanism underlying its exceptional photodamage resistance. In spite of its enormous growth and photosynthetic capabilities, C. ohadii is found in low abundance in its natural environment and was originally isolated as a contamination in a decaying culture of the filamentous cyanobacterium Leptolyngbya ohadii, an important primary producer in the BSCs. Using a tailor-made chamber simulating crust conditions, we show that ability of C. ohadii to revive after desiccation depends on close contact with L. ohadii, through a unique and novel mode of interspecies association. In view of the unparalleled growth and photosynthetic performance, C. ohadii may be used to clarify the processes that rate-limit growth and productivity of photosynthetic organisms. The biotechnological potential and uses are self-evident. [mehr]

Karsten Hiller

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June 2016

Uri Pick

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