Desir\u00e9e G\u00fctle d\u00e9fendra publiquement sa th\u00e8se\u00a0mercredi 29 mars \u00e0 9h\u00a0(amphi 7 FST).<\/p>\n
\u201c Characterization of the ferredoxin\/thioredoxin system and its targets in Physcomitrella patens<\/em><\/strong> \u201d<\/p>\n R\u00e9sum\u00e9<\/strong><\/p>\n La r\u00e9gulation redox est un m\u00e9canisme ancien pr\u00e9sent chez les organismes biologiques et impliqu\u00e9e dans diverses voies m\u00e9taboliques. En particulier chez les organismes photosynth\u00e9tiques elle est responsable des m\u00e9canismes d\u2019adaptation rapide dans un environnement constamment modifi\u00e9. Dans les chloroplastes le syst\u00e8me ferr\u00e9doxine\/thior\u00e9doxine est la cascade redox principale qui relie l\u2019activit\u00e9 de plusieurs enzymes plastidiales \u00e0 la source lumineuse. Le r\u00f4le central dans ce syst\u00e8me est jou\u00e9 par la ferr\u00e9doxine-thior\u00e9doxine r\u00e9ductase (FTR), une prot\u00e9ine h\u00e9t\u00e9rodim\u00e9rique qui r\u00e9cup\u00e8re des \u00e9lectrons \u00e0 partir de la ferr\u00e9doxine photor\u00e9duite et les transf\u00e8re pour r\u00e9duire des thior\u00e9doxines plastidiales. Ces prot\u00e9ines peuvent alors r\u00e9duire des enzymes cibles, requ\u00e9rant l\u2019accessibilit\u00e9 de paires de cyst\u00e9ines dans un disulfure dont la r\u00e9duction r\u00e9sulte en une activation\/ inactivation de la cible. Jusqu\u2019\u00e0 pr\u00e9sent des plantes viables n\u2019ont pu \u00eatre obtenues en l\u2019absence de ce syst\u00e8me de r\u00e9gulation. Dans cette th\u00e8se des secteurs du syst\u00e8me redox ont \u00e9t\u00e9 explor\u00e9s chez la plante mod\u00e8le Physcomitrella patens <\/em>(une mousse). Par manipulation de g\u00e8nes l\u2019influence de l\u2019enzyme FTR sur la croissance et le d\u00e9veloppement de la plante a \u00e9t\u00e9 analys\u00e9e suivant diff\u00e9rents param\u00e8tres. De mani\u00e8re \u00e0 impacter la fonction de la r\u00e9ductase des changements nucl\u00e9otidiques simples ont \u00e9t\u00e9 introduits au niveau des codons programmant les cyst\u00e9ines catalytiques et dans un deuxi\u00e8me temps le g\u00e8ne complet a \u00e9t\u00e9 supprim\u00e9. De fa\u00e7on inattendue nous n\u2019avons observ\u00e9 aucun effet significatif sur la viabilit\u00e9 et le d\u00e9veloppement des plantes mutantes. De plus, nous avons d\u00e9tect\u00e9 dans P. patens <\/em>des thior\u00e9doxines additionnelles absentes chez les plantes \u00e0 graine qui sont fonctionnelles vis \u00e0 vis des enzymes cibles mais non-r\u00e9duites par la FTR. Ceci rend possible un sc\u00e9nario de compensation chez les mutants via un syst\u00e8me de r\u00e9duction FTR-ind\u00e9pendant qui reste \u00e0 caract\u00e9riser. Deux des cibles photor\u00e9gul\u00e9es, la fructose-1,6-bisphosphatase (FBPase) et la s\u00e9doheptulose-1,7-bisphosphatase (SBPase), fonctionnent dans la phase de r\u00e9g\u00e9n\u00e9ration du cycle de Calvin-Benson cycle et elles poss\u00e8dent plusieurs caract\u00e9ristiques de catalyse et de r\u00e9gulation similaires. En combinant des approches biochimiques et structurales, une comparaison fonctionnelle et structurale des deux phosphatases de P. patens <\/em>a \u00e9t\u00e9 conduite. De plus l\u2019analyse phylog\u00e9n\u00e9tique a r\u00e9v\u00e9l\u00e9 une origine procaryotique ind\u00e9pendante des deux s\u00e9quences en d\u00e9pit de leurs similitudes structurales et catalytiques.<\/p>\n De plus trois articles de revue r\u00e9sument la plasticit\u00e9 et la repr\u00e9sentativit\u00e9 du mod\u00e8le P. patens <\/em>pour la recherche foresti\u00e8re, les principes g\u00e9n\u00e9raux de la r\u00e9gulation redox relativement aux aspects \u00e9volutifs et fonctionnels chez les plantes ainsi que l\u2019 \u00e9tat de l\u2019art de l\u00e9 r\u00e9gulation redox chez les esp\u00e8ces ligneuses en utilisant principalement le peuplier comme mod\u00e8le.<\/p>\n Mot cl\u00e8s: R\u00e9gulation redox, FTR syst\u00e8me, FBPase, SBPase, Physcomitrella patens<\/em><\/p>\n Abstract<\/strong><\/p>\n Redox regulation is an ancient mechanism present in biological organisms and is involved in diverse cellular pathways. In particular in photosynthetic organisms it is responsible for fast adaption mechanisms to a constantly changing environment. In chloroplasts the ferredoxin\/thioredoxin system represents the main redox regulatory cascade which links the activity of several plastid enzymes to the energy source, light. A central role in this system is played by the heterodimeric ferredoxin-thioredoxin reductase (FTR), which gains electrons from the photo-reduced ferredoxin and transfers those further on via<\/em> reduction to plastidal thioredoxins. Those proteins in turn reduce their target enzymes and require therefore the availability of redox sensitive cysteine pairs whose reduction results in an inactivation\/activation switch of the targets.<\/p>\n So far no viable plants could be obtained in complete absence of this redox regulation system. In this thesis single sections of the system were explored in the model plant Physcomitrella patens<\/em>. Through gene manipulation the influence of the FTR enzyme on plant growth and development was analysed. In order to impact on the function of the reductase, firstly single nucleotide exchange of the catalytic cysteines was performed and later on the\u00a0 gene was completely deleted. Surprisingly, no significant effect could be observed on the viability and development of mutant lines compared to WT plants. Furthermore we found that P.\u00a0patens<\/em> possesses in contrast to seed plants additional thioredoxins which are functional for reduction of FTR target enzymes but are most likely not supplied with electrons by this reductase. Thus a possible rescue scenario independent of FTR could be assumed for P.\u00a0patens<\/em> and also by other redox regulation systems present in chloroplasts.<\/p>\n Two of the FTR target enzymes, fructose-1,6-bisphosphatase and sedoheptulose-1,7-bisphosphatase, are functional in the regeneration phase of the Calvin-Benson cycle and share similar characteristics in regulation and catalysis. By combining biochemical and structural approaches a functional comparison of both phosphatases was conducted using cDNAs from P. patens<\/em>. A more strict TRX-dependent regulation and catalytic cleavage ability for both substrates, FBP and SBP, could be observed for SBPase, whereas FBPase is only capable of cleaving FBP. By obtaining the oxidized x-ray structure of both enzymes these observations can be associated with the distinct positions of regulatory sites and the various sizes of the substrate binding pocket. In addition, the phylogenetic analysis revealed an independent prokaryotic origin for both phosphatases.<\/p>\n Furthermore we summarized in three review articles the amenability of P. patens<\/em> as model plant for forest research, the general principles of redox regulation in respect of evolution and functional mechanisms in plants, and the current state of the art in forest redox regulation using poplar as exemplary model.<\/p>\n","protected":false},"excerpt":{"rendered":" Desir\u00e9e G\u00fctle d\u00e9fendra publiquement sa th\u00e8se\u00a0mercredi 29 mars \u00e0 9h\u00a0(amphi 7 FST). \u201c Characterization of the ferredoxin\/thioredoxin system and its targets in Physcomitrella patens \u201d R\u00e9sum\u00e9 La r\u00e9gulation redox est un m\u00e9canisme ancien pr\u00e9sent chez les organismes biologiques et impliqu\u00e9e … Continue reading