Light stress-regulated two-helix proteins in Arabidopsis thaliana related to the chlorophyll a/b-binding gene family

Abstract

The chlorophyll a͞b, chlorophyll a͞c, and chlorophyll a͞a light-harvesting proteins are part of an extended gene family that also includes the transiently expressed stress proteins, the Elips (early light-induced proteins). Four Elip homologue proteins, encoded by single-copy nuclear genes, have been identified in the Arabidopsis thaliana database. These proteins were divided into two groups according to the expression pattern under light-stress conditions and the predicted secondary structure. Group one included two members of the Elip family with three predicted transmembrane helices and a gene expression strictly related to light stress. Group two included two proteins, the Seps (stress-enhanced proteins), which possessed two predicted transmembrane segments. The transcripts of Sep1 and Sep2 were present under low light conditions, but their level increased 4-to 10-fold during illumination of plants with high-intensity light. Preliminary data indicated that the induced transcripts were translated in vivo. Other physiological stress conditions, such as cold, heat, desiccation, salt, wounding, or oxidative stress, did not significantly influence the expression of Sep genes. In vitro import of radioactively labeled precursors of Seps into isolated chloroplasts confirmed the thylakoid membrane localization of these proteins. Considering the predicted protein structure and homology to other pigment-antenna proteins, the two-helix Seps might represent an evolutionary missing link between the one-and three-helix antenna proteins present in pro-and eukaryota.ancestors ͉ chloroplast ͉ pigment proteins P hotosynthetic eukaryotes are traditionally divided into three major groups, largely on the basis of their light-harvesting antenna systems. The Chlorophytes (green algae and higher plants) have chlorophyll a͞b antennas, the Chromophytes have chlorophyll a͞c antennas, and the Rhodophytes (red algae) have only chlorophyll a and use phycobilisomes as the major photosystem (PS) II antenna (1, 2). The primary function of photosynthetic lightharvesting complexes is the absorption of light and the transfer of the excitation energy to the photochemical reaction centers. Because of their high sequence homology and similar structure and function, all of the eukaryotic light-harvesting antenna proteins are considered part of an extended gene family.The chlorophyll a͞b-binding (Cab) family in Arabidopsis thaliana contains at least 30 different members, associated with PSI or PSII (3). During the last few years, the Cab gene family was extended by the distant relatives, the PSII-S protein (4-6), the one-helix protein, the OHP (3), and the early light-induced proteins, the Elips (7, 8). The discovery of the cyanobacterial Hlip (high light-induced proteins) and the SCPs (small Cab-like proteins), clearly sharing the same conserved residues with the eukaryotic Cab proteins (9, 10), supported the idea that the prokaryotic Hlips and SCPs and the eukaryotic antenna proteins had a common ancestor (1, 11).The higher plant Elips are nuclear...

Induction of early light-inducible protein gene expression in Pisum sativum after exposure to low levels of UV-B irradiation and other environmental stresses

“…In Tortula ruralis, 50 mM of salt was enough to induce transcription of Elipa (Zeng et al 2002). However, in Arabidopsis thaliana, no induction of ELIP transcripts (Elipa and Elipb) was found after either wounding, salt, H 2 O 2 or heat-shock treatment (Heddad and Adamska 2000). We present here a rapid ELIP mRNA transcript accumulation in pea plants following salt and wounding, both stresses that are known to induce the production of oxidative species (León et al 2001;Xiong et al 2002).…”

“…1). This is the first report of UV-B-induced ELIP transcription, although induction by UV-A radiation has been shown (Adamska et al 1992;Heddad and Adamska 2000). ELIPs are thought to be involved in light-stress protection and are induced at both the transcript and the protein levels by different light stresses, such as high light, blue light, and UV-A radiation.…”

The early light-induced protein is also produced during leaf senescence of Nicotiana tabacum

“…Like other CAB family members, ELIP is localized to the chloroplast, but unlike other family members that are membrane-bound components of photosystems I and II, the ELIP protein is present only transiently in the thylakoid membranes (Grimm et al 1989;Heddad and Adamska 2000). However, ELIP has been shown to bind Chl and lutein, thereby implying that ELIP may be a pigment scavenger (Adamska et al 1999).…”

“…The probe for ELIP-TOB presumably would not hybridize with the mRNA for Seps (Fig. 1), stress-related members of the ELIP group from Arabidopsis described by Heddad and Adamska (2000), since Seps have only two transmembrane domains and are induced by light stress with dierent kinetics as compared with ELIPs.…”

Light-harvesting complexes of vascular plants

“…Since Lhc proteins of higher plants bind chlorophyll (Chl) a and b besides several carotenoid (Car) species, they are also called chlorophyll a+b-binding (cab) proteins. Lhc proteins form a multigene family together with one-helix proteins, stress-enhanced two-helix proteins, early light-inducible three-helix proteins, and the PsbS protein with four helices [6][7][8][9]. Although Lhc proteins possess a considerable amino acid identity/similarity in some regions, especially in the transmembrane regions, there are prominent differences in the overall amino acid sequences, which may be of importance with regard to functions exceeding the common functions of LHCs [6,10].…”