Consequences of the reduction of the Photosystem II antenna size on the light acclimation capacity of Arabidopsis thaliana.

Ludwik W Bielczynski,Gert Schansker,Roberta Croce

doi:10.1111/pce.13701

Abstract

In several systems, from plant's canopy to algal bioreactors, the decrease of the antenna size has been proposed as a strategy to increase the photosynthetic efficiency. However, still little is known about possible secondary effects of such modifications. This is particularly relevant because the modulation of the antenna size is one of the most important light acclimation responses in photosynthetic organisms. In our study, we used an Arabidopsis thaliana mutant (dLhcb2), which has a 60% decrease of Lhcb1 and Lhcb2, the two main components of the major Photosystem II antenna complex. We show that the mutant maintains the photosynthetic and photoprotective capacity of the Wild Type (WT) and adapts to different light conditions by remodelling its photosynthetic apparatus, but the regulatory mechanism differs from that of the WT. Surprisingly, it does not compensate for the decreased light‐harvesting capacity by increasing other pigment‐protein complexes. Instead, it lowers the ratio of the cytochrome b6f and ATP synthase to the photosystems, regulating linear electron flow and maintaining the photosynthetic control at the level of these complexes as in the WT. We show that targeting the reduction of two specific antenna proteins, Lhcb1 and Lhcb2, represents a viable solution to obtain plants with a truncated antenna size, which still maintain the capacity to acclimate to different light conditions.

Highlights

To meet the demand of the growing world population, the food production needs to be doubled until the end of this century, knowing that there are scarce prospects for the expansion of the cultivatable area (UN, 2015; Kline et al, 2017)
This is a promising strategy, it remained to be seen if the reduction of the antenna had negative effects on the functionality and acclimation capacity of the photosynthetic apparatus
In this work, we have focused on a mutant in which the Lhcb1 and Lhcb2 pool is only decreased

Summary

| INTRODUCTION

To meet the demand of the growing world population, the food production needs to be doubled until the end of this century, knowing that there are scarce prospects for the expansion of the cultivatable area (UN, 2015; Kline et al, 2017). Further from the core are located the minor antennae (CP24, CP26, and CP29, with 14 Chls a + b each), which, to the inner antennae, absorb light and transfer it to the RC They are the docking sites for the light-harvesting complexes II (LHCII) trimers, which are composed of the Lhcb proteins, and bind 42 Chls a + b (Ballottari, Girardon, Dall'Osto, & Bassi, 2012). Because LHCII modulation is a major acclimation strategy of plants (Anderson et al, 1995; Ballottari et al, 2007; Bielczynski et al, 2016; Wientjes, Van Amerongen, & Croce, 2013a), it was unclear if the absence of a part of the LHCIIs would influence the acclimation capacity of the plant To answer this question, we challenged a mutant having a smaller pool of LHCII (Andersson et al, 2003) to grow under different light conditions. Combining biochemical and functional measurements, we show that a targeted reduction of the LHCII pool is a viable strategy to decrease the antenna size without introducing secondary effects that negatively impact its performance

| MATERIALS AND METHODS

| RESULTS

Findings

| DISCUSSION