Phosphorylation-induced lateral rearrangements of thylakoid protein complexes upon light acclimation

Abstract

<p>Understanding the mechanistic basis of balanced excitation energy distribution<br />between photosystem II and photosystem I (PSII and PSI) requires detailed investigation<br />of the thylakoid light-harvesting system composed of energetically connected<br />LHCII trimers. The exact mechanisms controlling the excitation energy distribution<br />remain elusive, but reversible phosphorylation is known to be one important component.<br />Here, we addressed the role of grana margins in regulation of excitation<br />energy distribution, as these thylakoid domains host all the complexes of photosynthetic<br />light reactions with dynamic response to environmental cues. First, the effect<br />of detergents for the thylakoid membrane connectivity is explained. We show that<br />a specific interaction between the separate LHCII trimers as well as between the<br />LHCII trimers and the PSII and PSI–LHCI complexes is a prerequisite for energetically<br />connected and functional thylakoid membrane. Second, we demonstrate that<br />the optimization of light reactions under changing light conditions takes place in<br />energetically connected LHCII lake and is attained by lateral rearrangements of the<br />PSII–LHCII and PSI–LHCI–LHCII complexes depending especially on the phosphorylation<br />status of the LHCII protein isoform LHCB2.<br /></p>