The PsbS protein and low pH are necessary and sufficient to induce quenching in the light-harvesting complex of plants LHCII

Lauren Nicol,Roberta Croce

doi:10.1038/s41598-021-86975-9

Abstract

Photosynthesis is tightly regulated in order to withstand dynamic light environments. Under high light intensities, a mechanism known as non-photochemical quenching (NPQ) dissipates excess excitation energy, protecting the photosynthetic machinery from damage. An obstacle that lies in the way of understanding the molecular mechanism of NPQ is the large gap between in vitro and in vivo studies. On the one hand, the complexity of the photosynthetic membrane makes it challenging to obtain molecular information from in vivo experiments. On the other hand, a suitable in vitro system for the study of quenching is not available. Here we have developed a minimal NPQ system using proteoliposomes. With this, we demonstrate that the combination of low pH and PsbS is both necessary and sufficient to induce quenching in LHCII, the main antenna complex of plants. This proteoliposome system can be further exploited to gain more insight into how PsbS and other factors (e.g. zeaxanthin) influence the quenching mechanism observed in LHCII.

Highlights

Light absorption is maximized with specialized light-harvesting complexes (LHCs) that bind a high density of chlorophylls (Chls) and carotenoids
Arabidopsis thaliana PsbS knockout plants were transformed with PsbS modified to contain a strep-tag at the C terminus
These plants have a ~ 50% increase in the amount of qE compared to WT plants and a corresponding ~ 65% increase in the stoichiometry of PsbS to the Photosystem II (PSII) core, confirming that the non-photochemical quenching (NPQ) level increases with the increase of the amount of PsbS in the membrane and indicating that the strep-tag has minimal effect on PsbS function (Supplementary Fig. S1)

Summary

Introduction

Light absorption is maximized with specialized light-harvesting complexes (LHCs) that bind a high density of chlorophylls (Chls) and carotenoids. The absence of stably bound pigments suggests PsbS is not the site of quenching; the current view is that PsbS promotes the formation of quenching sites in the L HCs11 or at the interface between LHCs and P sbS12. This is supported by the substantial reduction of NPQ capacity in the absence of LHCs in vivo[13]. We aim to reproduce NPQ as it occurs in vivo i.e. fluorescence quenching that is both pH- and PsbS-dependent

Objectives

Methods

Results