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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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Expression of RedCAP and selected members from LHC and LHC-like protein families in diatoms. (A) Cells of P. tricornutum preadapted to LL (45 μmol photons·m−2·s−1) with illumination from 8 am to 12 midnight were either kept at LL conditions or transferred to D (no illumination) or ML (750 μmol photons ·m−2·s−1 throughout the illumination period) for 33 h and samples were collected every 3 h. Dark and light periods are indicated by grey or white bars, respectively, at the bottom of the expression data. (B) Cells of P. tricornutum preadapted to LL for 6 h (the first 6 h of the regular illumination period) were either kept at LL for additional 6 h or exposed to HL (1,500 to 2,000 μmol photons ·m−2·s−1) for 2 h and transferred back to LL for recovery (recov) for 4 h, samples were taken at the times indicated (relative to the transfer into HL). Relative transcript levels were calculated with help of the Relative Expression Software Tool REST [102] using the first sample of each light condition as a calibrator and 18 S rDNA as an endogenous control. The colour code indicates relative gene expression values as indicated by the scale bar on the right. Shown expression levels are average from four independent experiments, grey stars in the coloured boxes mark significant changes compared to the first sample as indicated by the statistical randomisation tests by REST [102].
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Figure 4: Expression of RedCAP and selected members from LHC and LHC-like protein families in diatoms. (A) Cells of P. tricornutum preadapted to LL (45 μmol photons·m−2·s−1) with illumination from 8 am to 12 midnight were either kept at LL conditions or transferred to D (no illumination) or ML (750 μmol photons ·m−2·s−1 throughout the illumination period) for 33 h and samples were collected every 3 h. Dark and light periods are indicated by grey or white bars, respectively, at the bottom of the expression data. (B) Cells of P. tricornutum preadapted to LL for 6 h (the first 6 h of the regular illumination period) were either kept at LL for additional 6 h or exposed to HL (1,500 to 2,000 μmol photons ·m−2·s−1) for 2 h and transferred back to LL for recovery (recov) for 4 h, samples were taken at the times indicated (relative to the transfer into HL). Relative transcript levels were calculated with help of the Relative Expression Software Tool REST [102] using the first sample of each light condition as a calibrator and 18 S rDNA as an endogenous control. The colour code indicates relative gene expression values as indicated by the scale bar on the right. Shown expression levels are average from four independent experiments, grey stars in the coloured boxes mark significant changes compared to the first sample as indicated by the statistical randomisation tests by REST [102].

Mentions: We investigated the expression of the P. tricornutum RedCAP gene and compared it to the expression of selected members of the LHC and LHC-like families. Cells were pre-adapted to low light (LL) at 16 h of daily illumination. With the onset of the dark period, cells were either kept in the same condition (LL) or transferred to continuous darkness (D) or moderate hight light (ML) for one regular 16 h illumination period. Transcript levels of selected genes were assayed in 3 h intervals throughout the following 33 h (Figure 4 and Table S3, see Additional file 9). In the LL condition (the regular culture condition), LHCF2 transcript levels were significantly down-regulated in the dark period and significantly up-regulated in the light period compared to the transcript level at the onset of darkness. This is consistent with previous reports of light dependent diurnal transcript regulation for this gene [36]. Following a similar pattern, also transcript levels of RedCAP and OHP1-like 1 were significantly up-regulated during the light period and down-regulated (no significant difference compared to the transcript level at the onset of darkness) during darkness. A similar expression pattern of RedCAP upon a shift from D to LL was recently reported [37]. In the D condition (no illumination) the amounts of LHCF2 and RedCAP transcripts were significantly down-regulated, although a transient up-regulation of the transcript level was measured at the time when the light was previously switched on, this effect was also observed (however, not statistically significant) for LHCF2 (Figure 4 and Table S3, see Additional file 9). In the ML condition (illumination with moderate hight light throughout the 16 h light period), RedCAP and LHCF2 transcripts were down-regulated compared to the transcript level at the onset of darkness, independent of the light or dark phase (Figure 4A, Figure S5 see Additional file 10). Thus, we can conclude that RedCAP and LHCF2 show a diurnal regulation of the gene expression at LL, which is not maintained in D or under ML illumination. This is in agreement with previous studies showing diurnal regulation of LHCF2 genes [36,38] and with the clustering of the P. tricornutum RedCAP gene with LHCF and LHCF-like genes in a hierarchical clustering analysis of diatom ESTs obtained from a range of different environmental conditions [39].


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)

Expression of RedCAP and selected members from LHC and LHC-like protein families in diatoms. (A) Cells of P. tricornutum preadapted to LL (45 μmol photons·m−2·s−1) with illumination from 8 am to 12 midnight were either kept at LL conditions or transferred to D (no illumination) or ML (750 μmol photons ·m−2·s−1 throughout the illumination period) for 33 h and samples were collected every 3 h. Dark and light periods are indicated by grey or white bars, respectively, at the bottom of the expression data. (B) Cells of P. tricornutum preadapted to LL for 6 h (the first 6 h of the regular illumination period) were either kept at LL for additional 6 h or exposed to HL (1,500 to 2,000 μmol photons ·m−2·s−1) for 2 h and transferred back to LL for recovery (recov) for 4 h, samples were taken at the times indicated (relative to the transfer into HL). Relative transcript levels were calculated with help of the Relative Expression Software Tool REST [102] using the first sample of each light condition as a calibrator and 18 S rDNA as an endogenous control. The colour code indicates relative gene expression values as indicated by the scale bar on the right. Shown expression levels are average from four independent experiments, grey stars in the coloured boxes mark significant changes compared to the first sample as indicated by the statistical randomisation tests by REST [102].
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Expression of RedCAP and selected members from LHC and LHC-like protein families in diatoms. (A) Cells of P. tricornutum preadapted to LL (45 μmol photons·m−2·s−1) with illumination from 8 am to 12 midnight were either kept at LL conditions or transferred to D (no illumination) or ML (750 μmol photons ·m−2·s−1 throughout the illumination period) for 33 h and samples were collected every 3 h. Dark and light periods are indicated by grey or white bars, respectively, at the bottom of the expression data. (B) Cells of P. tricornutum preadapted to LL for 6 h (the first 6 h of the regular illumination period) were either kept at LL for additional 6 h or exposed to HL (1,500 to 2,000 μmol photons ·m−2·s−1) for 2 h and transferred back to LL for recovery (recov) for 4 h, samples were taken at the times indicated (relative to the transfer into HL). Relative transcript levels were calculated with help of the Relative Expression Software Tool REST [102] using the first sample of each light condition as a calibrator and 18 S rDNA as an endogenous control. The colour code indicates relative gene expression values as indicated by the scale bar on the right. Shown expression levels are average from four independent experiments, grey stars in the coloured boxes mark significant changes compared to the first sample as indicated by the statistical randomisation tests by REST [102].
Mentions: We investigated the expression of the P. tricornutum RedCAP gene and compared it to the expression of selected members of the LHC and LHC-like families. Cells were pre-adapted to low light (LL) at 16 h of daily illumination. With the onset of the dark period, cells were either kept in the same condition (LL) or transferred to continuous darkness (D) or moderate hight light (ML) for one regular 16 h illumination period. Transcript levels of selected genes were assayed in 3 h intervals throughout the following 33 h (Figure 4 and Table S3, see Additional file 9). In the LL condition (the regular culture condition), LHCF2 transcript levels were significantly down-regulated in the dark period and significantly up-regulated in the light period compared to the transcript level at the onset of darkness. This is consistent with previous reports of light dependent diurnal transcript regulation for this gene [36]. Following a similar pattern, also transcript levels of RedCAP and OHP1-like 1 were significantly up-regulated during the light period and down-regulated (no significant difference compared to the transcript level at the onset of darkness) during darkness. A similar expression pattern of RedCAP upon a shift from D to LL was recently reported [37]. In the D condition (no illumination) the amounts of LHCF2 and RedCAP transcripts were significantly down-regulated, although a transient up-regulation of the transcript level was measured at the time when the light was previously switched on, this effect was also observed (however, not statistically significant) for LHCF2 (Figure 4 and Table S3, see Additional file 9). In the ML condition (illumination with moderate hight light throughout the 16 h light period), RedCAP and LHCF2 transcripts were down-regulated compared to the transcript level at the onset of darkness, independent of the light or dark phase (Figure 4A, Figure S5 see Additional file 10). Thus, we can conclude that RedCAP and LHCF2 show a diurnal regulation of the gene expression at LL, which is not maintained in D or under ML illumination. This is in agreement with previous studies showing diurnal regulation of LHCF2 genes [36,38] and with the clustering of the P. tricornutum RedCAP gene with LHCF and LHCF-like genes in a hierarchical clustering analysis of diatom ESTs obtained from a range of different environmental conditions [39].

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