DEPARTMENT of BIOLOGY at the UNIVERSITY of FRIBOURG
The Department of Biology is now composed of four functional groups - Biochemistry, Ecology and Evolution, Plant Biology and Zoology, each with several distinct research groups which you are invited to visit at the above links. Teaching at both the Bachelor and Master levels reflects the interests of the research groups and the respective programmes can be consulted using the appropriate links in the left column (in French and German for the Bachelor and in English for the Master).
Coming events & news
- 1st June: public presentation of PhD thesis
On the 1st June at 16.00h in lecture theatre 0.110 at Plant Biology, Museer Ahmad Lone will present the work entitled "Neutral lipid metabolism in Saccharomyces cerevisiae" which he carried out for the award of PhD. - Lorelise Branciard: public presentation of PhD thesis
On the 25th May at 15.30h in lecture theatre 0.110 at Plant Biology, Lorelise Branciard will present the work entitled "Functional analysis of Phytophthora brassicae RxLR-dEER effectors" which she carried out for the award of PhD. - Thursday 31st May: Symposium des travaux de bachelor
La présentation des travaux de Bachelor aura lieu de 8.15-11.45h et de 13.45-16.15h dans la salle de séminaires 0.109 de la Biologie végétale - Assemblée plénière du Département de Biologie
L'assemblée plénière du Département aura lieu jeudi, le 31 mai à 17.30h au grand auditoire de la Biologie végétale et sera suivie d'une grillade au Jardin Botanique. L'ordre du jour, etc., est disponible en utilisant le lien du titre.
Publication "hot spot"
S. Henrichs, B. Wang, Y. Fukao, J. Zhu, L. Charrier, A. Bailly, S.C. Oehring, M. Linnert,
M. Weiwad, A. Endler, P. Nanni, S. Pollmann, S. Mancuso, A. Schulz & M. Geisler (2012).Regulation of ABCB1/PGP1-catalysed auxin transport by linker phosphorylation. EMBO Journal (online, doi:10.1038/emboj.2012.120).
Polar transport of the plant hormone auxin is controlled by PIN- and ABCB/PGP-efflux catalysts. PIN polarity is regulated by the AGC protein kinase, PINOID (PID), while ABCB activity was shown to be dependent on interaction with the FKBP42, TWISTED DWARF1 (TWD1). Using co-immunoprecipitation (co-IP) and shotgun LC-MS/MS analysis, PID was identified as a valid partner in the interaction with TWD1. In-vitro and yeast expression analyses indicated that PID specifically modulates ABCB1-mediated auxin efflux in an action that is dependent on its kinase activity and that is reverted by quercetin binding and thus inhibition of PID autophosphorylation. Triple ABCB1/PID/TWD1 co-transfection in tobacco revealed that PID enhances ABCB1-mediated auxin efflux but blocks ABCB1 in the presence of TWD1. Phospho-proteomic analyses identified S634 as a key residue of the regulatory ABCB1 linker and a very likely target of PID phosphorylation that determines both transporter drug binding and activity. In summary, we provide evidence that PID phosphorylation has a dual, counter-active impact on ABCB1 activity that is coordinated by TWD1-PID interaction.
This publication is also the suject of a public presentation on the main University site.
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The phytohormone auxin acts as a prominent signal, providing, by its local accumulation or depletion in selected cells, a spatial and temporal reference for changes in the developmental program The distribution of auxin depends on both auxin metabolism (biosynthesis, conjugation and degradation) and cellular auxin transport. We identified in silico a novel putative auxin transport facilitator family, called PIN-LIKES (PILS). Here we illustrate that PILS proteins are required for auxin-dependent regulation of plant growth by determining the cellular sensitivity to auxin. PILS proteins regulate intracellular auxin accumulation at the endoplasmic reticulum and thus auxin availability for nuclear auxin signalling. PILS activity affects the level of endogenous auxin indole-3-acetic acid (IAA), presumably via intracellular accumulation and metabolism. Our findings reveal that the transport machinery to compartmentalize auxin within the cell is of an unexpected molecular complexity and demonstrate this compartmentalization to be functionally important for a number of developmental processes. |
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T Kretzschmar, W Kohlen, J Sasse, L Borghi, M Schlegel, JB Bachelier. D Reinhardt, R Bours, HJ Bouwmeester & E Martinoia. A petunia ABC protein controls strigolactone-dependent symbiotic signalling and branching. Nature 483: 341-344 (2012). Strigolactones were originally identified as stimulators of the germination of root-parasitic weeds that pose a serious threat to resource-limited agriculture. They are mostly exuded from roots and function as signalling compounds in the initiation of arbuscular mycorrhizae, which are plant-fungus symbionts with a global effect on carbon and phosphate cycling. Recently, strigolactones were established to be phytohormones that regulate plant shoot architecture by inhibiting the outgrowth of axillary buds. Despite their importance, it is not known how strigolactones are transported. ATP-binding cassette (ABC) transporters, however, are known to have functions in phytohormone translocation. Here we show that the Petunia hybrida ABC transporter PDR1 has a key role in regulating the development of arbuscular mycorrhizae and axillary branches, by functioning as a cellular strigolactone exporter. P. hybrida pdr1 mutants are defective in strigolactone exudation from their roots, resulting in reduced symbiotic interactions. Above ground, pdr1 mutants have an enhanced branching phenotype, which is indicative of impaired strigolactone allocation. Overexpression of Petunia axillaris PDR1 in Arabidopsis thaliana results in increased tolerance to high concentrations of a synthetic strigolactone, consistent with increased export of strigolactones from the roots. PDR1 is the first known component in strigolactone transport, providing new opportunities for investigating and manipulating strigolactone-dependent processes. |
The target of rapamycin complex 1 (TORC1) is an essential regulator of eukaryotic cell growth that responds to growth factors, energy levels, and amino acids. The mechanisms through which the preeminent amino acid leucine signals to the TORC1-regulatory Rag GTPases, which activate TORC1 within the yeast EGO complex (EGOC) or the structurally related mammalian Rag-Ragulator complex, remain elusive. We find that the leucyl-tRNA synthetase (LeuRS) Cdc60 interacts with the Rag GTPase Gtr1 of the EGOC in a leucine-dependent manner. This interaction is necessary and sufficient to mediate leucine signaling to TORC1 and is disrupted by the engagement of Cdc60 in editing mischarged tRNALeu. Thus, the EGOC-TORC1 signaling module samples, via the LeuRS-intrinsic editing domain, the fidelity of tRNALeu aminoacylation as a proxy for leucine availability. |
D Kierzkowski, N Nakayama, A-L Routier-Kierzkowska, A Weber, E Bayer, M Schorderet, D Reinhardt, C Kuhlemeier & RS Smith. Elastic domains regulate growth and organogenesis in the plant shoot apical meristem. Science 335: 1096-1099 (2012).
Although genetic control of morphogenesis is well established, elaboration of complex shapes requires changes in the mechanical properties of cells. In plants,the first visible sign of leaf formation is a bulge on the flank of the shoot apical meristem. Bulging results from local relaxation of cell walls, which causes them to yield to internal hydrostatic pressure. By manipulation of tissue tension in combination with quantitative live imaging and finite-element modeling, we found that the slow-growing area at the shoot tip is substantially strain-stiffened compared with surrounding fast-growing tissue. We propose that strain stiffening limits growth, restricts organ bulging, and contributes to the meristem's functional zonation. Thus, mechanical signals are not just passive readouts of gene action but feed back on morphogenesis.
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D Jeyaraj, FAJL Scheer, JA Ripperger, SM Haldar, Y Lu, DA Prosdocimo, SJ Eapen, BL Eapen, Y Cui, G H Mahabeleshwar, H Lee, MA Smith, G Casadesus, EM Mintz, H Sun, Y Wang, KM Ramsey, J Bass, SA Shea, U Albrecht, MK Jain. Klf15 orchestrates circadian nitrogen homeostasis. Cell Metabolism 15: 311-323 (2012).
Diurnal variation in nitrogen homeostasis is observed across phylogeny. But whether these are endogenous rhythms, and if so, molecular mechanisms that link nitrogen homeostasis to the circadian clock remain unknown. Here, we provide evidence that a clock-dependent peripheral oscillator, Krüppel-like factor 15 transcriptionally coordinates rhythmic expression of multiple enzymes involved in mammalian nitrogen homeostasis. In particular, Krüppel-like factor 15-deficient mice exhibit no discernable amino acid rhythm, and the rhythmicity of ammonia to urea detoxification is impaired. Of the external cues, feeding plays a dominant role in modulating Krüppel-like factor 15 rhythm and nitrogen homeostasis. Further, when all behavioral, environmental and dietary cues were controlled in humans, nitrogen homeostasis exhibited an endogenous circadian rhythmicity. Thus, in mammals, nitrogen homeostasis exhibits circadian rhythmicity, and is orchestrated by Krüppel-like factor 15. |
Albrecht U. Timing to perfection: the biology of central and peripheral circadian clocks. Neuron 74: 246-260 (2012). The mammalian circadian system, which is comprised of multiple cellular clocks located in the organs and tissues, orchestrates their regulation in a hierarchical manner throughout the 24 hr of the day. At the top of the hierarchy are the suprachiasmatic nuclei, which synchronize subordinate organ and tissue clocks using electrical, endocrine, and metabolic signaling pathways that impact the molecular mechanisms of cellular clocks. The interplay between the central neural and peripheral tissue clocks is not fully understood and remains a major challenge in determining how neurological and metabolic homeostasis is achieved across the sleep-wake cycle. Disturbances in the communication between the plethora of body clocks can desynchronize the circadian system, which is believed to contribute to the development of diseases such as obesity and neuropsychiatric disorders. This review will highlight the relationship between clocks and metabolism, and describe how cues such as light, food, and reward mediate entrainment of the circadian system. |
