Implication de la phosphoénolpyruvate carboxylase dans le métabolisme des graines et des feuilles d'Arabidopsis thaliana

LE PROJET CONCERNE L ETUDE DES ROLES DE LA PHOSPHOENOLPYRUVATE CARBOXYLASE DANS LES GRAINES ET FEUILLES D ARABIDOPSIS THALIANA. UNE APPROCHE GENETIQUE A ETE CHOISIE POUR RECHERCHER LES FONCTIONS DE L ENZYME IN VIVO.LES QUATRE GENES ATPPC SONT EXPRIMES SIMULTANEMENT DANS DIFFERENTS ORGANES VEGETAUX, ATPPC1-2 ET ATPPC3 ETANT MAJORITAIREMENT EXPRIMES RESPECTIVEMENT DANS LES ORGANES REPRODUCTEURS ET DANS LES RACINES. LE MUTANT D INSERTION POUR ATPPC2 PRESENTE UN PHENOTYPE MACROSCOPIQUE DE RETARD DE CROISSANCE.L ACTIVITE PEPC ET SA SENSIBILITE AU MALATE ONT ETE MESUREES AU COURS DU DEVELOPPEMENT DE LA GRAINE D A. THALIANA. LA PEPC SERAIT IMPLIQUEE DANS LA FOURNITURE DE SQUELETTES CARBONES POUR LA SYNTHESE DES RESERVES ET LEUR MOBILISATION A LA GERMINATION. DES LIGNEES TRANSFORMEES AVEC UN ADNC DE PEPC C4 ONT UNE ACTIVITE PEPC AUGMENTEE DANS LES GRAINES, DUE A L ISOFORME C4, QUI N A PAS D EFFET SUR LE POIDS, LES TENEURS EN AZOTE ET EN CARBONE TOTAL OU LES PROFILS DE PROTEINES. L AUGMENTATION D ACTIVITE PEPC EST CORRELEE NEGATIVEMENT AUX CONTENUS EN ACIDES GRAS ABONDANTS, EN ACIDES ORGANIQUES ET EN SACCHAROSE.AU NIVEAU DES FEUILLES, L ACTIVITE ENZYMATIQUE DANS LES PLANTES TRANSGENIQUES PEUT DIMINUER JUSQU A 25 %. LA COSUPPRESSION EST D AUTANT PLUS FORTE QUE L ACTIVITE DANS LES GRAINES EST ELEVEE. LA DIMINUTION DE L ENZYME EST CORRELEE A UNE DIMINUTION DE LA TENEUR EN MALATE, FUMARATE ET GLUTAMINE, CONFIRMANT LA FONCTION ANAPLEROTIQUE DE L ENZYME. EN CONDITION NORMALE DE CULTURE, LES PLANTES TRANSGENIQUES N ONT PAS DE PHENOTYPE MACROSCOPIQUE MAIS, SUR LITHIUM, ELLES MONTRENT UN RETARD DE CROISSANCE PLUS PRONONCE QUE LES PLANTES TEMOINS.PHOSPHOENOLPYRUVATE CARBOXYLASE IS A CENTRAL ENZYME IN PLANT METABOLISM. THIS WORK CONCERNS ITS PHYSIOLOGICAL ROLES, INVESTIGATED BY A GENETIC APPROACH IN SEEDS AND LEAVES OF A C3 PLANT, ARABIDOPSIS THALIANA.THE FOUR GENES ATPPC ARE CO-EXPRESSED IN DIFFERENT PLANT ORGANS AND EXPRESSION OF ATPPC1-2 AND ATPPC3 IS GREATER IN REPRODUCTIVE ORGANS AND ROOTS, RESPECTIVELY. GROWTH DELAY PHENOTYPE WAS OBTAINED WITH T-DNA INSERTION MUTANT IN ATPPC2 GENE.PEPC ACTIVITY AND MALATE SENSIBILITY WERE MEASURED DURING SEED DEVELOPMENT. ENZYMATIC ACTIVITY IS ELEVATED AT THE BEGINNING OF SEED FILLING AND AT THE END OF DEVELOPMENT, MALATE SENSIBILITY INCREASE DURING SEED MATURATION. PEPC COULD BE INVOLVED IN FURNISHING CARBON SKELETON TO STORAGE COMPOUNDS SYNTHESIS AND IN REMOBILISING STORAGE COMPOUNDS FOR GERMINATION.TRANSGENIC PLANTS, EXPRESSING A CDNA CODING FOR PEPC C4, HAVE ELEVATED SEEDS PEPC ACTIVITY LINKED TO A LARGE QUANTITY OF C4 ISOFORM. NO EFFECT WAS DETERMINED ON SEED WEIGHT, ON NITROGEN AND CARBON CONTENT OR ON SOLUBLE PROTEIN PROFILES. A NEGATIVE CORRELATION LINKS THE INCREASE OF PEPC ACTIVITY TO FATTY ACIDS, ORGANIC ACIDS AND SUCROSE CONTENTS.IN TRANSGENIC PLANTS LEAVES, PEPC ACTIVITY IS DIMINISHED AS FAR AS 25 % OF CONTROLS ACTIVITY. COSUPPRESSION IS EVEN MORE PRONOUNCED AS SEED ACTIVITY IS ELEVATED. PEPC DECREASE IS CORRELATED TO A DECREASE OF MALATE, FUMARATE AND GLUTAMINE CONTENTS, CONFIRMING ANAPLEROTIC FUNCTION OF PEPC. IN STANDARD CULTURE CONDITIONS, TRANSGENIC PLANTS HAVE NO MACROSCOPIC PHENOTYPE BUT SHOW A MORE PRONOUNCED GROWTH DELAY THAN CONTROLS DURING A LITHIUM STRESS.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF