The Vipp1 protein is essential in cyanobacteria and
chloroplasts for the maintenance of photosynthetic
function and thylakoid membrane architecture. To
investigate its mode of action we generated strains
of the cyanobacteria Synechocystis sp. PCC6803
and Synechococcus sp. PCC7942 in which Vipp1
was tagged with green fluorescent protein at the
C-terminus and expressed from the native chromosomal
locus. There was little perturbation of function. Live-cell fluorescence imaging shows dramatic relocalisation
of Vipp1 under high light. Under low light,
Vipp1 is predominantly dispersed in the cytoplasm
with occasional concentrations at the outer periphery
of the thylakoid membranes. High light induces Vipp1
coalescence into localised puncta within minutes, with
net relocation of Vipp1 to the vicinity of the cytoplasmic
membrane and the thylakoid membranes. Pulldowns
and mass spectrometry identify an extensive
collection of proteins that are directly or indirectly
associated with Vipp1 only after high-light exposure.
These include not only photosynthetic and stressrelated
proteins but also RNA-processing, translation
and protein assembly factors. This suggests that the
Vipp1 puncta could be involved in protein assembly.
One possibility is that Vipp1 is involved in the formation
of stress-induced localised protein assembly
centres, enabling enhanced protein synthesis and
delivery to membranes under stress conditions.