Plasticity in the Composition of the Light Harvesting Antenna of Higher Plants Preserves Structural Integrity and Biological Function

Alexander V Ruban,Svetlana Solovieva,Pamela J Lee,Cristian Ilioaia,Mark Wentworth,Ulrika Ganeteg,Frank Klimmek,Wah Soon Chow,Jan M Anderson,Stefan Jansson,Peter Horton

doi:10.1074/jbc.m511415200

Alexander V Ruban, Svetlana Solovieva + Show 9 more

Open Access

https://doi.org/10.1074/jbc.m511415200

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Abstract

Arabidopsis plants in which the major trimeric light harvesting complex (LHCIIb) is eliminated by antisense expression still exhibit the typical macrostructure of photosystem II in the granal membranes. Here the detailed analysis of the composition and the functional state of the light harvesting antennae of both photosystem I and II of these plants is presented. Two new populations of trimers were found, both functional in energy transfer to the PSII reaction center, a homotrimer of CP26 and a heterotrimer of CP26 and Lhcb3. These trimers possess characteristic features thought to be specific for the native LHCIIb trimers they are replacing: the long wavelength form of lutein and at least one extra chlorophyll b, but they were less stable. A new population of loosely bound LHCI was also found, contributing to an increased antenna size for photosystem I, which may in part compensate for the loss of the phosphorylated LHCIIb that can associate with this photosystem. Thus, the loss of LHCIIb has triggered concerted compensatory responses in the composition of antennae of both photosystems. These responses clearly show the importance of LHCIIb in the structure and assembly of the photosynthetic membrane and illustrate the extreme plasticity at the level of the composition of the light harvesting system.

Highlights

Adaptation strategy of plants, the state transitions, which control the relative PSI and PSII cross-sections [6]
The bands above 690 nm that belong to PSI [29] remains unchanged, because the spectra were normalized in this region. This picture is consistent with the fact that in asLhcb2 plants the amount of LHCII is reduced and the PSII to PSI ratio is strongly enhanced, i.e. there is a larger number of PSII units with a smaller antenna size [16]
This difference spectrum is explained by the reduction in content of LHCII, reducing the amount of energy transferred to the core and the amount of direct emission

Summary

Introduction

Adaptation strategy of plants, the state transitions, which control the relative PSI and PSII cross-sections [6]. Biochemical analysis showed that the levels of other antenna proteins increase in the antisense plants, and we suggested that the trimers are composed of the greatly increased amounts of Lhcb, which is normally only found in the monomeric CP26 complex These observations led to the hypothesis that the increases in expression of other light harvesting genes may be compensatory changes that allow the thylakoid membrane structure to be preserved and photosynthetic performance to be maintained. Plasticity in the Light Harvesting Antenna feature of the molecular design of the functional thylakoid membrane If this hypothesis is correct, these responses indicate the presence of a remarkable level of plasticity and robustness, which must result from a complex response of the altered LHC genome in the form of interplay between the expression of both Lhcb and Lhca genes and in the processes of assembly of supramolecular structure.

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