Elucidating VIPP function in thylakoid biogenesis with VIPPaccumulating mutants as entry point

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VIPP1 (originally termed vesicle inducing protein in plastids 1) is important for the biogenesis of thylakoid membranes (TMs), as Arabidopsis knock-out mutants lack thylakoid membranes and knockdown mutants contain fewer TMs and TM protein complexes. VIPPs overaccumulate in Chlamydomonas cells exposed to high-light intensities and in mutants with reduced levels of proteins involved in the translocation/ integration of TM proteins (alb3.1, secA). This suggests that the role of VIPP1 during TM biogenesis might not be at the level of membrane biogenesis via vesicle formation, but rather at the level of the biogenesis/repair of TM protein complexes. Based on these findings we performed a forward genetics screen with Chlamydomonas reinhardtii to identify mutants that constitutively overexpress VIPPs. As all mutants analyzed so far (7 out of 13) have defects in the accumulation of subunits of the four major TM protein complexes and/or in the repair of photosystem II from photodamage, this indeed indicates a role for VIPPs in TM protein complex biogenesis/repair. In this project we wish to characterize these mutants in detail to (i) learn about the roles of the affected genes in TM protein complex biogenesis/repair and (ii) understand why and how their functions are supported by VIPPs. Moreover, having identified a lipid component to which recombinant VIPPs strongly bind, we wish to investigate the role of this lipid component for VIPP membrane binding and oligomerization in vitro and in vivo.