Adapting to the right light: In plants, photosystem II is the first protein complex in the machinery that converts sunlight into chemical energy. It comprises antennae complexes (LHCIIs), which collect the light energy, and a dimeric core that contains the reaction center where water is split into oxygen and protons. Su et al. report cryo-electron microscopy structures of a supercomplex consisting of the dimeric core, two strongly bound LHCIIs, and two moderately bound LHCIIs (see the Perspective by Croce and van Amerongen). Under high-light conditions, the moderately bound LHCIIs might detach to down-regulate the efficiency of light harvesting and prevent damage. Science , this issue p. 815 ; see also p. 752

Antenna switches partners in the shade: A cloudy day or an overshadowing tree causes fluctuations in light that can throw off the balance of energy flow in plant photosystems I and II (PSI and PSII). Pan et al. solved structures of PSI bound to two light-harvesting complexes (LHCs). One LHC is permanently associated with PSI. The other LHC delivers light energy to PSII under optimal conditions but can switch to a PSI-associated state after phosphorylation by a kinase that senses the redox environment of the chloroplast. The movement of LHCs between the photosystems helps maintain even energy flux. Two chlorophyll-containing subunits are visible in the structure that connect the PSI core to each LHC. Science , this issue p. 1109

NAD(P)H dehydrogenase-like (NDH) complex NDH-1L of cyanobacteria plays a crucial role in cyclic electron flow (CEF) around photosystem I and respiration processes. NDH-1L couples the electron transport from ferredoxin (Fd) to plastoquinone (PQ) and proton pumping from cytoplasm to the lumen that drives the ATP production. NDH-1L-dependent CEF increases the ATP/NADPH ratio, and is therefore pivotal for oxygenic phototrophs to function under stress. Here we report two structures of NDH-1L from Thermosynechococcus elongatus BP-1, in complex with one Fd and an endogenous PQ, respectively. Our structures represent the complete model of cyanobacterial NDH-1L, revealing the binding manner of NDH-1L with Fd and PQ, as well as the structural elements crucial for proper functioning of the NDH-1L complex. Together, our data provides deep insights into the electron transport from Fd to PQ, and its coupling with proton translocation in NDH-1L.

The structures of cyanobacterial and vascular plant phosphoribulokinase, alone and in complex, provide insights into the mechanisms by which the oxygenic photos