Le rôle de la signalisation à travers les pectines dans le contrôle de la croissance et la réponse aux stress

par Fan Xu

Projet de thèse en Biologie

Sous la direction de Herman Hofte.

Thèses en préparation à Paris Saclay , dans le cadre de Sciences du Végétal : du gène à l'écosystème , en partenariat avec IJPB Institut Jean-Pierre Bourgin (laboratoire) , Pôle PAVE: Paroi végétale, fonction et usage (equipe de recherche) et de Université Paris-Sud (établissement de préparation de la thèse) depuis le 12-10-2015 .

  • Titre traduit

    The Role of Pectin Signaling in the Control of Growth and Stress Responses

  • Résumé

    Plant cell walls play an active role in growth and development and in the response to abiotic and biotic stresses. Pectins are a major class of cellwall polysaccharides characterized by the presence of Galacturonic acid (GalA). Homogalacturonan is a linear pectic homopolymer of alpha-1,4-linked GalA. This polymer is synthesized in the Golgi apparatus in a highly methylesterified form and subsequently de-methylesterified by pectin methyl esterases (PME) in the cell wall. PME activity is highly regulated in part through the interaction of the PME enzymes with endogenous PME inhibitors (PMEIs). Low degree of methylesterification (DM) pectin can form Ca2+ links, which contribute to wall stiffening. On the other hand, the host laboratory has recently shown that depending on the context, PME activity also can promote wall loosening, cell expansion and organ formation. In addition to this, plants have the ability to monitor the pectin methylesterification status. This involves receptor like kinases and receptor like proteins, which control growth through the triggering of brassinosteroid signalling, but also responses to biotic and abiotic stresses. During my thesis I will investigate how different PMEs can promote either wall stiffening or loosening and how the action of different PMEs can trigger signalling responses or not. To this end I will develop an inducible expression system to express a subset of the 66 Arabidopsis PMEIs in N. benthamiana and Arabidopsis and investigate the response of the plant to the inhibition of PME activity, in particular the activation of the brassinosteroid signalling pathway. I will next select PMEIs that have contrasting effects, identify the PMEs that they inhibit and study their in vivo activity, including the changes in pectin methylesterification that they bring about. Finally I will study how these changes play a role in the response of the plant to pathogens (e.g. Botrytis cinerea). This work should lead to a better understanding of the wall signalling processes that control plant growth and responses to pathogens.