High‐light versus low‐light: Effects on paired photosystem ii supercomplex structural rearrangement in pea plants

In plant grana thylakoid membranes Photosystem II (PSII) associates with a variable number of antenna proteins (LHCII) to form different types of supercomplexes (PSII‐LHCII), whose organization is dynamically adjusted in response to light cues, with the C2S2 more abundant in high-light and the C2S2M2 in low‐light. Paired PSII‐LHCII supercomplexes interacting at their stromal surface from adjacent thylakoid membranes were previously suggested to mediate grana stacking. Here, we present the cryo‐electron microscopy maps of paired C2S2 and C2S2M2 supercomplexes isolated from pea plants grown in high‐light and low‐light, respectively. These maps show a different rotational offset between the two supercomplexes in the pair, responsible for modifying their reciprocal interaction and energetic connectivity. This evidence reveals a different way by which paired PSII‐LHCII supercomplexes can mediate grana stacking at diverse irradiances. Electrostatic stromal interactions between LHCII trimers almost completely overlapping in the paired C2S2 can be the main determinant by which PSII‐LHCII supercomplexes mediate grana stacking in plants grown in high‐light, whereas the mutual interaction of stromal N‐terminal loops of two facing Lhcb4 subunits in the paired C2S2M2 can fulfil this task in plants grown in low‐light. The high‐light induced accumulation of the Lhcb4.3 protein in PSII‐LHCII supercomplexes has been previously reported. Our cryo‐electron microscopy map at 3.8 Å resolution of the C2S2 supercomplex isolated from plants grown in high‐light suggests the presence of the Lhcb4.3 protein revealing peculiar structural features of this high‐light‐specific antenna important for photoprotection.