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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 xanthophyll cycle-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 ZEP1 (A), ZEP2 (B), ZEP3 (C), VDE (D), VDL1 (E) and VDL2 (F) were determined after 1, 3, 5, 8 and 12h by qPCR 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-g007: mRNA levels of xanthophyll cycle-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 ZEP1 (A), ZEP2 (B), ZEP3 (C), VDE (D), VDL1 (E) and VDL2 (F) were determined after 1, 3, 5, 8 and 12h by qPCR 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: We also determined the steady state transcript levels of the P. tricornutum ZEPs and VDEs in 48 h dark-adapted cells subsequently shifted to either white, blue and red light as described above (Fig. 7). We found a steady and strong increase of ZEP1 transcript levels after 5 hours of white and blue light, and after this period the levels decreased again. The effect of white light was stronger than blue light, and red light did not result in a significant induction (Fig. 7A). The increase in ZEP2 levels is approximately 10-fold lower than ZEP1, but the kinetics of ZEP2 accumulation is faster and maximal levels were reached within 5 h of illumination (Fig. 7B). Blue light appears to have a stronger effect on ZEP2 transcription than white light, even though the white light fluence rate was 7 times higher. Contrary to ZEP1, red light also has a slight effect on ZEP2 transcript levels. ZEP3 mRNA accumulation showed different kinetics, in which a minor induction after 1 h white or blue light was followed by a 2 h lag-phase (Fig. 7C). Maximal ZEP3 transcript levels were found after 5 h of blue light and after 8 h of white light. VDE transcript levels very rapidly increased after stimulation with blue and white light and close to maximal levels were reached within 1h (Fig. 7D). The overall kinetics of steady-state VDE mRNA levels was much like ZEP3 (Fig. 7C,D). These two genes are located next to each other on chromosome 8 (Fig. 7G) and are likely to form a co-regulated gene-cluster. Another such gene cluster is found on chromosome 4 composed of ZEP1 and VDL2, and also in this case the transcript levels of the two clustered genes were comparable (Fig. 7A,F,G).


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 xanthophyll cycle-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 ZEP1 (A), ZEP2 (B), ZEP3 (C), VDE (D), VDL1 (E) and VDL2 (F) were determined after 1, 3, 5, 8 and 12h by qPCR 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

Show All Figures
getmorefigures.php?uid=PMC2483416&req=5

pone-0002896-g007: mRNA levels of xanthophyll cycle-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 ZEP1 (A), ZEP2 (B), ZEP3 (C), VDE (D), VDL1 (E) and VDL2 (F) were determined after 1, 3, 5, 8 and 12h by qPCR 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: We also determined the steady state transcript levels of the P. tricornutum ZEPs and VDEs in 48 h dark-adapted cells subsequently shifted to either white, blue and red light as described above (Fig. 7). We found a steady and strong increase of ZEP1 transcript levels after 5 hours of white and blue light, and after this period the levels decreased again. The effect of white light was stronger than blue light, and red light did not result in a significant induction (Fig. 7A). The increase in ZEP2 levels is approximately 10-fold lower than ZEP1, but the kinetics of ZEP2 accumulation is faster and maximal levels were reached within 5 h of illumination (Fig. 7B). Blue light appears to have a stronger effect on ZEP2 transcription than white light, even though the white light fluence rate was 7 times higher. Contrary to ZEP1, red light also has a slight effect on ZEP2 transcript levels. ZEP3 mRNA accumulation showed different kinetics, in which a minor induction after 1 h white or blue light was followed by a 2 h lag-phase (Fig. 7C). Maximal ZEP3 transcript levels were found after 5 h of blue light and after 8 h of white light. VDE transcript levels very rapidly increased after stimulation with blue and white light and close to maximal levels were reached within 1h (Fig. 7D). The overall kinetics of steady-state VDE mRNA levels was much like ZEP3 (Fig. 7C,D). These two genes are located next to each other on chromosome 8 (Fig. 7G) and are likely to form a co-regulated gene-cluster. Another such gene cluster is found on chromosome 4 composed of ZEP1 and VDL2, and also in this case the transcript levels of the two clustered genes were comparable (Fig. 7A,F,G).

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