Séminaire IBIP
Les séminaires ont lieu sur le Campus Montpellier SupAgro/INRA de La Gaillarde (2, place P. Viala Montpellier)

Jeudi 14 février 2008
Amphi 206 (Cœur d’Ecole) à 14h

Copper Delivery for Photosynthesis: Transporters, Metallo-Chaperones and Regulation by Small RNA

Marinus Pilon
Biology Department, Colorado State University, Fort Collins, CO 80523, USA.
Chercheur en séjour sabbatique-BPMP

About a third of all proteins require a metal ion cofactor for activity. The growth environment often limits the availability of metal cofactors. Under limitation cells must prioritize delivery to specific targets and coordinate delivery with apo-protein expression as well as varying metabolic demand. Targets for copper (Cu) delivery in plant chloroplasts are plastocyanin in the thylakoids and Cu/Zn-superoxide dismutase (Cu/ZnSOD) in the stroma. PAA1 and PAA2 encode Cu-transporting P-type ATPases in the chloroplast. Characterization of paa1 and paa2 mutants showed that the two transporters have distinct functions. Both transporters are required for Cu delivery to plastocyanin and efficient photosynthetic electron transport. However, Cu delivery to the stroma is only inhibited in paa1 but not in paa2 mutants. Localization experiments indicated that both transportersfunction in chloroplasts and that the PAA1 protein is in the chloroplast periphery whereas PAA2 functions in the thylakoids. A paa1paa2 double mutant was seedling lethal and could not be rescued by Cu feeding. A third component of the Cu delivery system in chloroplasts is CCS, a Cu-chaperone that delivers Cu to Cu/ZnSOD. Next to Cu/ZnSOD, plants have a FeSOD in the chloroplast. Interestingly, Cu availability regulates the activity of the SOD isoforms and the CCS metallo-chaperone. At low Cu levels, the FeSOD is active and Cu/ZnSOD and CCS expression is shut off, so that Cu is preferentially targeted to plastocyanin, which is essential in plants. At higher Cu levels, FeSOD expression is shut off, saving Fe for other uses, and Cu/Zn SOD becomes a sink for Cu in the stroma. We found a signaling pathway, which senses the Cu that is available to the chloroplast and which mediates the microRNA-mediated down-regulation of non-essential nuclear-encoded Cu-proteins under Cu limitation.

Contact : Cathy Curie

Contacts IBIP :
Sabine Zimmermann
Marc Lepetit
Corinne Dasen
Chantal Baracco