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.

June 2016

Uri Pick - How are triacylglycerides produced in the green alga Dunaliella tertiolecta?

Green microalgae accumulate under stress conditions such as nitrogen limitation either starch or triacylglycerides (TAG) or both. The biosynthesis of TAG is of special interest because it is a potential source for production of biodiesel. However, there are still large gaps in our understanding about the enzymatic pathways of TAG biosynthesis and how it is controlled. This work was designed to clarify two issues in triacylglyceride (TAG) biosynthesis in green algae: what is the major rate-limiting stage in TAG biosynthesis and how much fatty acids (FA) that are channeled for TAG biosynthesis are produced de novo, from pre-formed polar lipids (PL) or from degradation of starch. The work was performed in the halotolerant alga Dunaliella tertiolecta by pulse labeling with 14C-palmitic acid (PA) and with 14C-bicarbonate. The results show that: (i) FA biosynthesis is the rate-limiting stage in TAG biosynthesis and it precedes the activation of glycerol transacylation into TAG, (ii) degradation of pre-formed lipids provides less than 10% of the FA in TAG, (iii) starch provides over 90% of the carbon for FA biosynthesis and as such is the major carbon source for FA and TAG biosynthesis under N deprivation, (iv) under control (+N) conditions, most FA are initially incorporated into phosphatidylcholine (PC). Under N deprivation incorporation into PC is inhibited, whereas incorporation into digalactosyldiacylglycerol (DGDG) is enhanced, suggesting that DGDG serves as an intermediate in acyl transfer into TAG. The significance of these results for our understanding of TAG biosynthesis and for future advances in improving TAG productivity in algae will be discussed. [mehr]

Pierre Baldet - Strategies for Deciphering the Metabolism of Ascorbic Acid (vitamin C) in Tomato

Ascorbic acid (vitamin C) is a major antioxidant in plants, and fruits are the major source of this vitamin for humans. While the pathways of synthesis, recycling and degradation are well characterized, their regulation is still poorly understood. We have used reverse genetic approaches to target two key steps of the Wheeler & Smirnoff synthesis pathway: GDP-D-mannose epimerase (GME) and GDP-L-galactose phosphorylase (GGP) in tomato fruits. In addition to a reduction of ascorbic acid content, RNAi-silenced gme tomato lines exhibited growth phenotypes resulting from cell division and expansion defects, exacerbated fragility and loss of fruit firmness related to modifications of the cell wall structure and composition [1,2]. These findings help to explain observed links between seemingly unrelated quality traits such as fruit firmness and ascorbic acid content. Two ggp knockout lines were identified from TILLING (EMS) mutant populations. These have reduced ascorbic content and show bleaching and leaf necrosis after short exposure to high light [3,4]. Integration of transcriptomic, proteomic, and metabolomic data from wild type and mutant tomato fruits identified candidate genes involved in the regulation of the ascorbate pathway [5]. A forward genetic screen has identified four mutant lines which have 2.5 to 5-fold higher levels of ascorbic acid than wild-type, and one candidate gene has been mapped using next generation sequencing approaches. [1] Gilbert L, Alhagdow M, Nunes-Nesi A, Quemener B, Guillon F, Bouchet B, Faurobert M, Gouble B, Page D, Garcia V, Petit J, Stevens R, Causse M, Fernie AR, Lahaye M, Rothan C and Baldet P. (2009). Plant J. 60, 499-508. [2] Voxeur A, Gilbert L, Rihouey C, Driouich A, Rothan C, Baldet P and Lerouge P (2011). Journal of Biological Chemistry, 286: 8014-8020. [3] Okabe Y, Asamizu E., Saito T., Matsukura C., Ariizumi T., Bres C., Rothan C., Mizoguchi T. and Ezura H. (2011). Plant Cell Physiol. 52(11): 1994–2005. [4] Just D., Garcia V., Fernandez L., Bres C., Mauxion JP., Petit J., Jorly J., Assali J., Bournonville C., Ferrand C., Baldet P., Lemaire-Chamley M., Mori K., Okabe Y., Ariizumi T., Asamizu E., Ezura H., and Rothan C. (2013). Plant Biotech. 30, 225-231. [5] Garcia V., Stevens R., Gil L., Gilbert L., Gest N., Petit J., Faurobert M., Maucourt M., Deborde C., Moing A., Poessel JL., Jacob D., Bouchet JP., Giraudel JL., Gouble B., Page D., Alhagdow M., Massot C., Gautier H., Lemaire-Chamley M., de Daruvar A., Rolin D., Usadel B., Lahaye M., Causse M., Baldet P. and Rothan C. (2009). Compte rendu de Biologie. 332, 1007-1021. [mehr]

Hans-Henning Kunz - Using the chloroplast envelope carrier mutant kea1kea2 to probe the impact of abiotic stress on photosynthesis and the plant ion homeostasis

Drought and soil salinity represent two tightly linked abiotic stress factors. Together they by far cause the most damaging effects on annual crop yields. Although evidence for the importance of the chloroplast in surviving these adverse environmental effects have existed for years still the molecular processes are not well understood. Recently, several independent laboratories have started to investigate the plastid ion transport mechanisms. Particularly K+ flux was found to be crucial in maintaining the chloroplast ion and pH homeostasis and to fine-tune photosynthesis. This carefully balanced system can be readily disturbed by abiotic stress. For instance, during salt stress toxic Na ions also accumulate in chloroplasts, where they replace K+ ions and diminish photosynthetic efficiency in plants. This could supposedly be prevented by controlling the ion flux across the envelope membrane via ion carries and channels. The kea1kea2 mutant that lacks two highly active K+/H+ antiporters is strongly growth compromised with poor photosynthesis under normal growth conditions. However, if exposed to soil salinity mutants flourish with highly recovered photosynthetic efficiency. My lab is interested in deciphering the molecular foundation of this phenomenon. By doing so, we anticipate to find the missing ion transport mechanisms in the envelope membrane. In my seminar I will show some early data on how we approach this endeavor and what we plan to do in the next few years. [mehr]

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