Subproject 3

Functions of CURT1 proteins in thylakoid grana formation

Project leader: Prof. Dr. Dario Leister

Chloroplasts of land plants characteristically contain grana, cylindrical stacks of thylakoid membranes. The mechanisms leading to the formation of grana, and in particular the factors that generate the extreme curvature in grana margins are largely unknown. In previous work we have identified a small family of proteins, designated CURT1, which is required for grana formation. Because overexpresion of CURT1 proteins increases the number of membrane layers in grana, the CURT1 proteins are highly enriched in grana margins, and CURT1 proteins can induce tubulation of liposomes in vitro, we conclude that these proteins are directly involved in inducing/maintained the membrane curvature in margins. The five central questions which will be addressed in this project are: 1. By which mechanism do CURT1 proteins bend membranes? 2. What is the role of phosphorylation of thylakoid proteins (including CURT1) in grana stacking? 3. How has the grana stacking function of CURT1 protein evolutionary developed? 4. Is CURT1 sufficient in vivo to mediate grana stacking? Which other factors are involved? 5. What is the physiological relevance, in particular under natural conditions, of grana stacking? To address these questions we will apply methods from molecular genetics, molecular biology, biochemistry and electron microscopy (EM) and study several model species, in particular Arabidopsis thaliana, Synechocystis 6803 and Chlamydomonas reinhardtii.