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Evolutionary origins and functions of the carotenoid biosynthetic pathway in marine diatoms.

Coesel S, Oborník M, Varela J, Falciatore A, Bowler C - PLoS ONE (2008)

Bottom Line: Consistent with the supplemental xanthophyll cycle in diatoms, we found more copies of the genes encoding violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP) enzymes compared with other photosynthetic eukaryotes.Protein domain structures and expression analyses in the pennate diatom Phaeodactylum tricornutum indicate diverse roles for the different ZEP and VDE isoforms and demonstrate that they are differentially regulated by light.These studies therefore reveal the ancient origins of several components of the carotenoid biosynthesis pathway in photosynthetic eukaryotes and provide information about how they have diversified and acquired new functions in the diatoms.

View Article: PubMed Central - PubMed

Affiliation: Cell Signalling Laboratory, Stazione Zoologica Anton Dohrn, Villa Comunale, Naples, Italy.

ABSTRACT
Carotenoids are produced by all photosynthetic organisms, where they play essential roles in light harvesting and photoprotection. The carotenoid biosynthetic pathway of diatoms is largely unstudied, but is of particular interest because these organisms have a very different evolutionary history with respect to the Plantae and are thought to be derived from an ancient secondary endosymbiosis between heterotrophic and autotrophic eukaryotes. Furthermore, diatoms have an additional xanthophyll-based cycle for dissipating excess light energy with respect to green algae and higher plants. To explore the origins and functions of the carotenoid pathway in diatoms we searched for genes encoding pathway components in the recently completed genome sequences of two marine diatoms. Consistent with the supplemental xanthophyll cycle in diatoms, we found more copies of the genes encoding violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP) enzymes compared with other photosynthetic eukaryotes. However, the similarity of these enzymes with those of higher plants indicates that they had very probably diversified before the secondary endosymbiosis had occurred, implying that VDE and ZEP represent early eukaryotic innovations in the Plantae. Consequently, the diatom chromist lineage likely obtained all paralogues of ZEP and VDE genes during the process of secondary endosymbiosis by gene transfer from the nucleus of the algal endosymbiont to the host nucleus. Furthermore, the presence of a ZEP gene in Tetrahymena thermophila provides the first evidence for a secondary plastid gene encoded in a heterotrophic ciliate, providing support for the chromalveolate hypothesis. Protein domain structures and expression analyses in the pennate diatom Phaeodactylum tricornutum indicate diverse roles for the different ZEP and VDE isoforms and demonstrate that they are differentially regulated by light. These studies therefore reveal the ancient origins of several components of the carotenoid biosynthesis pathway in photosynthetic eukaryotes and provide information about how they have diversified and acquired new functions in the diatoms.

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mRNA levels of carotenoid biosynthesis and LHC-related genes upon white, blue or red light stimulation.48-hour-dark-adapted P. tricornutum cells were exposed to 175 µmol m−2 s−1 continuous white light, or 25 µmol m−2 s−1 continuous blue or red light and the relative transcript levels of PSY (A), PDS1 (B), FCPB (C) and ELIP-like (D) were determined after 1, 3, 5, 8 and 12h by qRT-PCR using H4 as a reference gene. The values were normalized to the transcript levels in the dark. Data are averages of triplicate measurements. The error bars represent standard deviation.
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pone-0002896-g006: mRNA levels of carotenoid biosynthesis and LHC-related genes upon white, blue or red light stimulation.48-hour-dark-adapted P. tricornutum cells were exposed to 175 µmol m−2 s−1 continuous white light, or 25 µmol m−2 s−1 continuous blue or red light and the relative transcript levels of PSY (A), PDS1 (B), FCPB (C) and ELIP-like (D) were determined after 1, 3, 5, 8 and 12h by qRT-PCR using H4 as a reference gene. The values were normalized to the transcript levels in the dark. Data are averages of triplicate measurements. The error bars represent standard deviation.

Mentions: The steady state transcript levels of 48 hour dark-adapted P. tricornutum cells treated with either continuous white (175 µmol m−2 s−1), blue (25 µmol m−2 s−1) or red (25 µmol m−2 s−1) light were determined for 12 subsequent hours by quantitative real-time PCR (qRT-PCR) using histone H4 (H4) as a reference gene [9]. The transcript levels of both PSY and PDS1 increased immediately upon light exposure (Fig. 6), and the highest steady state transcript levels were measured after 3 to 5 h light. Transcript levels decreased again after longer exposure. The transcript levels of PDS1 and, to a lesser degree, of PSY are similar at 25 µmol m−2 s−1 blue light and 175 µmol m−2 s−1 white light, indicating that the spectral quality of light plays a major role in the regulation of expression of these genes. This observation is further supported by the fact that red light, with an equal fluence rate as blue light, triggered a much weaker response. The induction of the two genes encoding LHC proteins, FCPB and ELIP-like, began slightly later than the carotenogenesis-related genes (Fig. 6). However, the amplitude of induction was more than 100-fold higher than for PSY and PDS1. The spectral quality of light was also of major influence for these genes: the transcript levels of both genes in blue and white light were similar, but the kinetics of increase were faster in blue light than in white light. By contrast, the amplitude and kinetics of transcription in response to red light were much lower.


Evolutionary origins and functions of the carotenoid biosynthetic pathway in marine diatoms.

Coesel S, Oborník M, Varela J, Falciatore A, Bowler C - PLoS ONE (2008)

mRNA levels of carotenoid biosynthesis and LHC-related genes upon white, blue or red light stimulation.48-hour-dark-adapted P. tricornutum cells were exposed to 175 µmol m−2 s−1 continuous white light, or 25 µmol m−2 s−1 continuous blue or red light and the relative transcript levels of PSY (A), PDS1 (B), FCPB (C) and ELIP-like (D) were determined after 1, 3, 5, 8 and 12h by qRT-PCR using H4 as a reference gene. The values were normalized to the transcript levels in the dark. Data are averages of triplicate measurements. The error bars represent standard deviation.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2483416&req=5

pone-0002896-g006: mRNA levels of carotenoid biosynthesis and LHC-related genes upon white, blue or red light stimulation.48-hour-dark-adapted P. tricornutum cells were exposed to 175 µmol m−2 s−1 continuous white light, or 25 µmol m−2 s−1 continuous blue or red light and the relative transcript levels of PSY (A), PDS1 (B), FCPB (C) and ELIP-like (D) were determined after 1, 3, 5, 8 and 12h by qRT-PCR using H4 as a reference gene. The values were normalized to the transcript levels in the dark. Data are averages of triplicate measurements. The error bars represent standard deviation.
Mentions: The steady state transcript levels of 48 hour dark-adapted P. tricornutum cells treated with either continuous white (175 µmol m−2 s−1), blue (25 µmol m−2 s−1) or red (25 µmol m−2 s−1) light were determined for 12 subsequent hours by quantitative real-time PCR (qRT-PCR) using histone H4 (H4) as a reference gene [9]. The transcript levels of both PSY and PDS1 increased immediately upon light exposure (Fig. 6), and the highest steady state transcript levels were measured after 3 to 5 h light. Transcript levels decreased again after longer exposure. The transcript levels of PDS1 and, to a lesser degree, of PSY are similar at 25 µmol m−2 s−1 blue light and 175 µmol m−2 s−1 white light, indicating that the spectral quality of light plays a major role in the regulation of expression of these genes. This observation is further supported by the fact that red light, with an equal fluence rate as blue light, triggered a much weaker response. The induction of the two genes encoding LHC proteins, FCPB and ELIP-like, began slightly later than the carotenogenesis-related genes (Fig. 6). However, the amplitude of induction was more than 100-fold higher than for PSY and PDS1. The spectral quality of light was also of major influence for these genes: the transcript levels of both genes in blue and white light were similar, but the kinetics of increase were faster in blue light than in white light. By contrast, the amplitude and kinetics of transcription in response to red light were much lower.

Bottom Line: Consistent with the supplemental xanthophyll cycle in diatoms, we found more copies of the genes encoding violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP) enzymes compared with other photosynthetic eukaryotes.Protein domain structures and expression analyses in the pennate diatom Phaeodactylum tricornutum indicate diverse roles for the different ZEP and VDE isoforms and demonstrate that they are differentially regulated by light.These studies therefore reveal the ancient origins of several components of the carotenoid biosynthesis pathway in photosynthetic eukaryotes and provide information about how they have diversified and acquired new functions in the diatoms.

View Article: PubMed Central - PubMed

Affiliation: Cell Signalling Laboratory, Stazione Zoologica Anton Dohrn, Villa Comunale, Naples, Italy.

ABSTRACT
Carotenoids are produced by all photosynthetic organisms, where they play essential roles in light harvesting and photoprotection. The carotenoid biosynthetic pathway of diatoms is largely unstudied, but is of particular interest because these organisms have a very different evolutionary history with respect to the Plantae and are thought to be derived from an ancient secondary endosymbiosis between heterotrophic and autotrophic eukaryotes. Furthermore, diatoms have an additional xanthophyll-based cycle for dissipating excess light energy with respect to green algae and higher plants. To explore the origins and functions of the carotenoid pathway in diatoms we searched for genes encoding pathway components in the recently completed genome sequences of two marine diatoms. Consistent with the supplemental xanthophyll cycle in diatoms, we found more copies of the genes encoding violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP) enzymes compared with other photosynthetic eukaryotes. However, the similarity of these enzymes with those of higher plants indicates that they had very probably diversified before the secondary endosymbiosis had occurred, implying that VDE and ZEP represent early eukaryotic innovations in the Plantae. Consequently, the diatom chromist lineage likely obtained all paralogues of ZEP and VDE genes during the process of secondary endosymbiosis by gene transfer from the nucleus of the algal endosymbiont to the host nucleus. Furthermore, the presence of a ZEP gene in Tetrahymena thermophila provides the first evidence for a secondary plastid gene encoded in a heterotrophic ciliate, providing support for the chromalveolate hypothesis. Protein domain structures and expression analyses in the pennate diatom Phaeodactylum tricornutum indicate diverse roles for the different ZEP and VDE isoforms and demonstrate that they are differentially regulated by light. These studies therefore reveal the ancient origins of several components of the carotenoid biosynthesis pathway in photosynthetic eukaryotes and provide information about how they have diversified and acquired new functions in the diatoms.

Show MeSH