Multimeric and monomeric photosystem II supercomplexes represent structural adaptations to low- and high-light conditions

Eunchul Kim,Akimasa Watanabe,Christopher D.P Duffy,Alexander V Ruban,Jun Minagawa

doi:10.1074/jbc.ra120.014198

Abstract

An intriguing molecular architecture called the "semi-crystalline photosystem II (PSII) array" has been observed in the thylakoid membranes in vascular plants. It is an array of PSII-light-harvesting complex II (LHCII) supercomplexes that only appears in low light, but its functional role has not been clarified. Here, we identified PSII-LHCII supercomplexes in their monomeric and multimeric forms in low light-acclimated spinach leaves and prepared them using sucrose-density gradient ultracentrifugation in the presence of amphipol A8-35. When the leaves were acclimated to high light, only the monomeric forms were present, suggesting that the multimeric forms represent a structural adaptation to low light and that disaggregation of the PSII-LHCII supercomplex represents an adaptation to high light. Single-particle EM revealed that the multimeric PSII-LHCII supercomplexes are composed of two ("megacomplex") or three ("arraycomplex") units of PSII-LHCII supercomplexes, which likely constitute a fraction of the semi-crystalline PSII array. Further characterization with fluorescence analysis revealed that multimeric forms have a higher light-harvesting capability but a lower thermal dissipation capability than the monomeric form. These findings suggest that the configurational conversion of PSII-LHCII supercomplexes may serve as a structural basis for acclimation of plants to environmental light.

Highlights

Light is an important energy resource for photosynthetic organisms, but its quality and quantity are variable in the field [1]
Because the polypeptide compositions in A4 and A5 were essentially identical to that of A3 (Fig. 1B), we presumed that the A4 and A5 bands corresponded to multimers of photosystem II (PSII)–light-harvesting complex II (LHCII) supercomplexes
The lower two bands (A4 and A5 bands) were not detected in the sample prepared from the HL-treated leaves, whereas the upper three bands (A1, A2 and A3) stayed the same (Fig. 1A), suggesting that the putative multimeric PSII–LHCII supercomplexes (A4 and A5) were only present in the leaves acclimated to LL conditions

Summary

Introduction

Light is an important energy resource for photosynthetic organisms, but its quality and quantity are variable in the field [1]. The LL-dependent formation of the possible multimeric forms of PSII–LHCII supercomplexes was reminiscent of the formation of semi-crystalline PSII arrays observed in LL-adapted leaves [6].

Results

Conclusion