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A novel type of light-harvesting antenna protein of red algal origin in algae with secondary plastids.

Sturm S, Engelken J, Gruber A, Vugrinec S, Kroth PG, Adamska I, Lavaud J - BMC Evol. Biol. (2013)

Bottom Line: Members of the extended light-harvesting complex (LHC) protein superfamily are involved in light harvesting as well as in photoprotection and are found in the red and green plant lineages, with a complex distribution pattern of subfamilies in the different algal lineages.The occurrence of RedCAPs was found to be restricted to the red algal lineage, including red algae (with primary plastids) as well as cryptophytes, haptophytes and heterokontophytes (with secondary plastids of red algal origin).In their proposed function, the RedCAP protein family may thus have played a role in the evolutionary structural remodelling of light-harvesting antennae in the red lineage.

View Article: PubMed Central - HTML - PubMed

Affiliation: Ökophysiologie der Pflanzen, Fach 611, Universität Konstanz, 78457 Konstanz, Germany.

ABSTRACT

Background: Light, the driving force of photosynthesis, can be harmful when present in excess; therefore, any light harvesting system requires photoprotection. Members of the extended light-harvesting complex (LHC) protein superfamily are involved in light harvesting as well as in photoprotection and are found in the red and green plant lineages, with a complex distribution pattern of subfamilies in the different algal lineages.

Results: Here, we demonstrate that the recently discovered "red lineage chlorophyll a/b-binding-like proteins" (RedCAPs) form a monophyletic family within this protein superfamily. The occurrence of RedCAPs was found to be restricted to the red algal lineage, including red algae (with primary plastids) as well as cryptophytes, haptophytes and heterokontophytes (with secondary plastids of red algal origin). Expression of a full-length RedCAP:GFP fusion construct in the diatom Phaeodactylum tricornutum confirmed the predicted plastid localisation of RedCAPs. Furthermore, we observed that similarly to the fucoxanthin chlorophyll a/c-binding light-harvesting antenna proteins also RedCAP transcripts in diatoms were regulated in a diurnal way at standard light conditions and strongly repressed at high light intensities.

Conclusions: The absence of RedCAPs from the green lineage implies that RedCAPs evolved in the red lineage after separation from the the green lineage. During the evolution of secondary plastids, RedCAP genes therefore must have been transferred from the nucleus of the endocytobiotic alga to the nucleus of the host cell, a process that involved complementation with pre-sequences allowing import of the gene product into the secondary plastid bound by four membranes. Based on light-dependent transcription and on localisation data, we propose that RedCAPs might participate in the light (intensity and quality)-dependent structural or functional reorganisation of the light-harvesting antennae of the photosystems upon dark to light shifts as regularly experienced by diatoms in nature. Remarkably, in plastids of the red lineage as well as in green lineage plastids, the phycobilisome based cyanobacterial light harvesting system has been replaced by light harvesting systems that are based on members of the extended LHC protein superfamily, either for one of the photosystems (PS I of red algae) or for both (diatoms). In their proposed function, the RedCAP protein family may thus have played a role in the evolutionary structural remodelling of light-harvesting antennae in the red lineage.

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Localisation of the RedCAP protein in complex plastids of diatoms.(A) Bipartite plastid targeting sequences in photosynthetic Chromista. The conserved “ASAFAP”-motif [32,33] at the interface between signal and transit peptides is marked. (B) Sequence of the Phaeodactylum tricornutum RedCAP full length GFP fusion construct. (C) Expression of the full-length RedCAP:GFP fusion constructs in P. tricornutum. (D) Expression of GFP without targeting pre-sequence in P. tricornutum. Panels show microscopical images of transmitted light (differential interference contrast, DIC), chlorophyll autofluorescence, GFP fluorescence and a merged image from left to right, fluorescence images are maximum intensity projections of 14 slices of a 4.9 μm image stack, scale bars represent 10 μm.
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Figure 3: Localisation of the RedCAP protein in complex plastids of diatoms.(A) Bipartite plastid targeting sequences in photosynthetic Chromista. The conserved “ASAFAP”-motif [32,33] at the interface between signal and transit peptides is marked. (B) Sequence of the Phaeodactylum tricornutum RedCAP full length GFP fusion construct. (C) Expression of the full-length RedCAP:GFP fusion constructs in P. tricornutum. (D) Expression of GFP without targeting pre-sequence in P. tricornutum. Panels show microscopical images of transmitted light (differential interference contrast, DIC), chlorophyll autofluorescence, GFP fluorescence and a merged image from left to right, fluorescence images are maximum intensity projections of 14 slices of a 4.9 μm image stack, scale bars represent 10 μm.

Mentions: All identified RedCAPs in algae with secondary plastids were nuclear-encoded and include an N-terminal bipartite pre-sequence, consisting of a signal and a transit peptide domain and a conserved “ASAFAP”-motif located at the interface between both domains, which is required for import through the four membranes surrounding such plastids [32,33]. This suggests a plastid location of RedCAPs (Figure 3A). To verify the predicted location experimentally, we fused the full-length RedCAP sequence to the green fluorescent protein (GFP) gene (Figure 3B) and expressed it in the diatom Phaeodactylum tricornutum. Analysis of the GFP signal by confocal fluorescence microscopy revealed that this signal co-localised with the red Chl autofluorescence (Figure 3C, Figure S4, see Additional file 8), thus confirming a plastid localisation of RedCAP in diatoms.


A novel type of light-harvesting antenna protein of red algal origin in algae with secondary plastids.

Sturm S, Engelken J, Gruber A, Vugrinec S, Kroth PG, Adamska I, Lavaud J - BMC Evol. Biol. (2013)

Localisation of the RedCAP protein in complex plastids of diatoms.(A) Bipartite plastid targeting sequences in photosynthetic Chromista. The conserved “ASAFAP”-motif [32,33] at the interface between signal and transit peptides is marked. (B) Sequence of the Phaeodactylum tricornutum RedCAP full length GFP fusion construct. (C) Expression of the full-length RedCAP:GFP fusion constructs in P. tricornutum. (D) Expression of GFP without targeting pre-sequence in P. tricornutum. Panels show microscopical images of transmitted light (differential interference contrast, DIC), chlorophyll autofluorescence, GFP fluorescence and a merged image from left to right, fluorescence images are maximum intensity projections of 14 slices of a 4.9 μm image stack, scale bars represent 10 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750529&req=5

Figure 3: Localisation of the RedCAP protein in complex plastids of diatoms.(A) Bipartite plastid targeting sequences in photosynthetic Chromista. The conserved “ASAFAP”-motif [32,33] at the interface between signal and transit peptides is marked. (B) Sequence of the Phaeodactylum tricornutum RedCAP full length GFP fusion construct. (C) Expression of the full-length RedCAP:GFP fusion constructs in P. tricornutum. (D) Expression of GFP without targeting pre-sequence in P. tricornutum. Panels show microscopical images of transmitted light (differential interference contrast, DIC), chlorophyll autofluorescence, GFP fluorescence and a merged image from left to right, fluorescence images are maximum intensity projections of 14 slices of a 4.9 μm image stack, scale bars represent 10 μm.
Mentions: All identified RedCAPs in algae with secondary plastids were nuclear-encoded and include an N-terminal bipartite pre-sequence, consisting of a signal and a transit peptide domain and a conserved “ASAFAP”-motif located at the interface between both domains, which is required for import through the four membranes surrounding such plastids [32,33]. This suggests a plastid location of RedCAPs (Figure 3A). To verify the predicted location experimentally, we fused the full-length RedCAP sequence to the green fluorescent protein (GFP) gene (Figure 3B) and expressed it in the diatom Phaeodactylum tricornutum. Analysis of the GFP signal by confocal fluorescence microscopy revealed that this signal co-localised with the red Chl autofluorescence (Figure 3C, Figure S4, see Additional file 8), thus confirming a plastid localisation of RedCAP in diatoms.

Bottom Line: Members of the extended light-harvesting complex (LHC) protein superfamily are involved in light harvesting as well as in photoprotection and are found in the red and green plant lineages, with a complex distribution pattern of subfamilies in the different algal lineages.The occurrence of RedCAPs was found to be restricted to the red algal lineage, including red algae (with primary plastids) as well as cryptophytes, haptophytes and heterokontophytes (with secondary plastids of red algal origin).In their proposed function, the RedCAP protein family may thus have played a role in the evolutionary structural remodelling of light-harvesting antennae in the red lineage.

View Article: PubMed Central - HTML - PubMed

Affiliation: Ökophysiologie der Pflanzen, Fach 611, Universität Konstanz, 78457 Konstanz, Germany.

ABSTRACT

Background: Light, the driving force of photosynthesis, can be harmful when present in excess; therefore, any light harvesting system requires photoprotection. Members of the extended light-harvesting complex (LHC) protein superfamily are involved in light harvesting as well as in photoprotection and are found in the red and green plant lineages, with a complex distribution pattern of subfamilies in the different algal lineages.

Results: Here, we demonstrate that the recently discovered "red lineage chlorophyll a/b-binding-like proteins" (RedCAPs) form a monophyletic family within this protein superfamily. The occurrence of RedCAPs was found to be restricted to the red algal lineage, including red algae (with primary plastids) as well as cryptophytes, haptophytes and heterokontophytes (with secondary plastids of red algal origin). Expression of a full-length RedCAP:GFP fusion construct in the diatom Phaeodactylum tricornutum confirmed the predicted plastid localisation of RedCAPs. Furthermore, we observed that similarly to the fucoxanthin chlorophyll a/c-binding light-harvesting antenna proteins also RedCAP transcripts in diatoms were regulated in a diurnal way at standard light conditions and strongly repressed at high light intensities.

Conclusions: The absence of RedCAPs from the green lineage implies that RedCAPs evolved in the red lineage after separation from the the green lineage. During the evolution of secondary plastids, RedCAP genes therefore must have been transferred from the nucleus of the endocytobiotic alga to the nucleus of the host cell, a process that involved complementation with pre-sequences allowing import of the gene product into the secondary plastid bound by four membranes. Based on light-dependent transcription and on localisation data, we propose that RedCAPs might participate in the light (intensity and quality)-dependent structural or functional reorganisation of the light-harvesting antennae of the photosystems upon dark to light shifts as regularly experienced by diatoms in nature. Remarkably, in plastids of the red lineage as well as in green lineage plastids, the phycobilisome based cyanobacterial light harvesting system has been replaced by light harvesting systems that are based on members of the extended LHC protein superfamily, either for one of the photosystems (PS I of red algae) or for both (diatoms). In their proposed function, the RedCAP protein family may thus have played a role in the evolutionary structural remodelling of light-harvesting antennae in the red lineage.

Show MeSH
Related in: MedlinePlus