A guide to the Lhc genes and their relatives in Arabidopsis

doi:10.1016/S1360-1385(99)01419-3

Trends in Plant Science

Volume 4, Issue 6, 1 June 1999, Pages 236-240

https://doi.org/10.1016/S1360-1385(99)01419-3 Get rights and content

Abstract

The Lhc super-gene family encodes the light-harvesting chlorophyll a/b-binding (LHC) proteins that constitute the antenna system of the photosynthetic apparatus, and also includes some relatives whose functions are more or less unknown. The Lhc super-gene family of Arabidopsis contains >30 members and the databases contain >1000 EST clones originating from these genes. This article presents an overview of these genes and provides some tools for researchers who want to use them in their studies.

Section snippets

EST clones originating from the Lhc super-gene family

The Arabidopsis genome project has already produced an immense amount of data and the full genomic sequence will soon be available. Many of the EST clones currently available (30 000 EST sequences are accessible in the public databases and the corresponding clones can be ordered from the Arabidopsis Stock Center) correspond to Lhc genes, both from the ten that had previously been characterized (five Lhcb1 and one each of Lhca1, Lhca2, Lhca3, Lhca4 and Lhcb4) and from additional members of the

Lhca genes

Lhca1–4 genes encode the polypeptides of light-harvesting complex I (LHC I) associated with PSI. LHC I is composed of dimers of Lhca proteins but the numbers and exact positions of these dimers have not been determined. An Arabidopsis Lhca1 gene was the first to be sequenced⁶ and Lhca3 (Ref. 7) and Lhca4 (Ref. 8) cDNAs have subsequently been analysed. An Lhca2 sequence has also been reported⁹ but the encoded protein is different from other Lhca2 gene products. There is no EST clone

Lhcb1–3 genes

The Lhcb1, Lhcb2 and Lhcb3 genes encode the polypeptides of trimeric LHC II. Lhcb1 homotrimers and Lhcb1/Lhcb2 heterotrimers function as antenna for both photosystems, whereas trimers containing Lhcb3 (probably 2Lhcb1/Lhcb3) appear to be confined to PSII.

Five Lhcb1 genes have been characterized previously from Arabidopsis11, 12 and all Lhcb1 EST clones appear to originate from these genes, indicating that no additional Lhcb1 genes are present. There are large differences in the expression

Lhcb4–6 genes

The Lhcb4, Lhcb5 and Lhcb6 proteins (often called CP29, CP26 and CP24, respectively) are probably monomeric proteins that are present in one copy per PSII unit. One Lhcb4 gene has been sequenced¹³, but two additional Lhcb4 genes are present in Arabidopsis. Two genes have about the same level of expression, whereas the third (Lhcb4.3) is expressed only at a low level. The protein encoded by Lhcb4.3 is different from the other two proteins in that it lacks a large part of the C-terminal region

The cousins, PsbS and ELIPs

Two proteins with homology to the LHC proteins, PsbS and early light-inducible proteins (ELIPs), have been characterized from higher plants previously. This similarity is not only at the sequence level, as both have been shown recently to bind chlorophyll and carotenoids¹⁵. All Arabidopsis PsbS EST clones appear to originate from a single gene. The ELIPs are also three-helix members of the super-gene family, and probably associated with PSII. The ELIP EST clones fall into two groups, indicating

Novel members of the family

Analysis of EST clones has resulted in the identification of several novel sequences with significant sequence homology to the Lhc genes. A common feature of all these genes is that they encode proteins with one, not two, ‘generic LHC motifs' in their sequences (Fig. 3). The first of these has been used for more extensive studies, and it transpires that the encoded protein is a single-helix thylakoid protein of 7 kDa (S. Jansson et al., unpublished). The closest homologues to this protein in

Concluding remarks

An analysis of the EST clones present in the public databases has revealed that the LHC super-gene family of Arabidopsis contains >30 members, of which some encode proteins that were previously unknown. Some of these might have a role in high-light acclimation – ongoing studies will clarify this. Do these 30 genes represent the complete super-gene family? It is unlikely that there are additional genes encoding proteins in unit stoichiometry in PSI or PSII, but the possibility that there could

Acknowledgements

My thanks to Ulrika Ganeteg for sequencing EST clones, to Iwona Adamska who generously shared unpublished data and to Vaughan Hurry who commented on the manuscript. Financial support was provided by the Swedish Forestry and Agricultural Research Council and the Foundation for Strategic Research. Finally, this work would not have been possible without the excellent services of the Arabidopsis Biological Resource Center (ABRC) in Ohio, USA.

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Trends in Plant Science

PerspectivesA guide to the Lhc genes and their relatives in Arabidopsis

Abstract

Section snippets

EST clones originating from the Lhc super-gene family

Lhca genes

Lhcb1–3 genes

Lhcb4–6 genes

The cousins, PsbS and ELIPs

Novel members of the family

Concluding remarks

Acknowledgements

Biochim. Biophys. Acta

Molecular cloning and sequencing of cDNA encoding the precursor to the small subunit of chloroplast ribulose-1,5-bisphosphate carboxylase

Nature

A nomenclature for the genes encoding the chlorophyll a/b-binding proteins of higher plants

Plant Mol. Biol. Rep.

Atomic model of plant light-harvesting complex

Nature

Cyanobacterial protein with similarity to the chlorophyll a/b binding-proteins of higher plants: evolution and regulation

Proc. Natl. Acad. Sci. U. S. A.

Hypothesis for the evolution of three-helix Chl a/b and Chl a/c light-harvesting antenna proteins from two-helix and four-helix ancestors

Photosynth. Res.

Identification of a single-copy gene encoding a type I chlorophyll a/b-binding polypeptide of photosystem I in Arabidopsis thaliana

Physiol. Plant.

An Arabidopsis cab gene homologous to Cab-8 of tomato

Plant Physiol.

Isolation, characterization, and chromosomal location of a new cab gene from Arabidopsis thaliana

Plant Physiol.

Differential expression in Arabidopsis of Lhca2, a PSI cab gene

Plant Mol. Biol.

Structure and expression of three light-harvesting chlorophyll a/b-binding protein genes in Arabidopsis thaliana

Nucleic Acids Res.

Perspectives
A guide to the Lhc genes and their relatives in Arabidopsis