| iCal Calendar Event Reminder | 11:00 - 12:30 | Thursday, January 15, 2009 |
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| Event Text: | Prof. Dr. Peter G. Kroth Department of Biology University of Konstanz Konstanz GERMANY "The Peculiar Physiology and Cell Biology of diatoms" |
| Event Date: | Thursday, January 15, 2009 |
| Event Time: | 11:00 - 12:30 |
| Popup Text: | ABSTRACT "The Peculiar Physiology and Cell Biology of diatoms" Diatoms are fascinating organisms for several reasons. They are ecologically very impor-tant, they live inside ornate silicified cell walls and they evolved by secondary endocyto-biosis, a process in which a eukaryotic alga was incorporated into a eukaryotic host cell, followed by transformation of the endosymbiont into a plastid. Especially this evolutionary process resulted in various differences with respect to the physiology and cell biology of these algae when compared to green algae and land plants. In this presentation I will mainly focus on three aspects of diatom biology: (i) Diatom plastids have four envelope membranes, the outermost being continuous with the endoplasmic reticulum and commonly referred to as the ???chloroplast ER??? or ???CER???. In vivo-analyses of protein targeting utilizing presequence:G FP fusion proteins expressed in Phaeodactylum tricornutum indicate that protein targeting across the four membranes de-pends on N-terminal bipartite presequences consisting of a signal and a transit peptide domain. Chromalveolates like diatoms or cryptophytes share a conserved amino acid mo-tif at the signal peptide???s cleavage site, often containing an "ASAFAP" motif. Experimental data showed the particular importance of a single phenylalanine at the N-terminus of the transit peptide for successful plastid targeting. (ii) In land plants the Calvin cycle is regulated by small proteins termed thioredoxins representing a ???light switch??? for CO2 fixation. We found that for most of the known target enzymes for thioredoxin regulation in land plants, the respective enzymes in diatoms are not regulated by thioredoxin. In addition essential pathways like the oxidative pentose phosphate pathway and others apparently have been moved intracellularly within the diatom cells. (iii) New molecular tools to study diatoms have been developed in then recent years in-cluding genome sequencing and transformation techniques. |