Stereochemistry of phytoene biosynthesis by isolated chloroplasts.
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ABSTRACT:
SUBMITTER: Buggy MJ
PROVIDER: S-EPMC1184938 | biostudies-other | 1969 Sep
REPOSITORIES: biostudies-other
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Project description:1. Chloroplasts prepared by the non-aqueous technique will, after fragmentation by ultrasonic treatment, incorporate [2-(14)C]mevalonic acid into phytoene, the first C(40) compound formed in the biosynthetic sequence to coloured carotenoids. 2. With suspensions containing 3.5mg. of chlorophyll, the optimum amounts of cofactor required were ATP (10mumoles), magnesium chloride (20mumoles) and glutathione (20mumoles); neither NAD(+) nor NADP(+) was required. 3. Very small amounts of squalene are also formed and synthesis is stimulated by addition of NADH or NADPH. Phytoene synthesis was not affected by the presence of these cofactors and no lycopersene (the C(40) homologue of squalene) was detected. 4. The phytol side chain of chlorophyll is also labelled under these conditions. 5. Preparations of developing chloroplasts are more active than preparations of mature chloroplasts.
| S-EPMC1198291 | biostudies-other
Project description:[2-(14)C,(2R)-2-(3)H(1)]- and [2-(14)C,(2S)-2-(3)H(1)]-Mevalonates were rapidly incorporated into phytoene, lycopene, rubixanthin and zeaxanthin in a Flavobacterium system obtained by disruption of the bacterial cells by shaking with glass beads. Four hydrogen atoms arising from the 2-pro-S-hydrogen atoms of mevalonate were lost in the desaturation of phytoene to lycopene, rubixanthin and zeaxanthin. The desaturation of phytoene involves trans-elimination of hydrogen in the introduction of the double bonds at C-7, C-11, C-7' and C-11'.
| S-EPMC1177920 | biostudies-other
Project description:The isolation and characterization of the phytoene synthase gene from the green microalga Chlorella zofingiensis (CzPSY), involved in the first step of the carotenoids biosynthetic pathway, have been performed. CzPSY gene encodes a polypeptide of 420 amino acids. A single copy of CzPSY has been found in C. zofingiensis by Southern blot analysis. Heterologous genetic complementation in Escherichia coli showed the ability of the predicted protein to catalyze the condensation of two molecules of geranylgeranyl pyrophosphate (GGPP) to form phytoene. Phylogenetic analysis has shown that the deduced protein forms a cluster with the rest of the phytoene synthases (PSY) of the chlorophycean microalgae studied, being very closely related to PSY of plants. This new isolated gene has been adequately inserted in a vector and expressed in Chlamydomonas reinhardtii. The overexpression of CzPSY in C. reinhardtii, by nuclear transformation, has led to an increase in the corresponding CzPSY transcript level as well as in the content of the carotenoids violaxanthin and lutein which were 2.0- and 2.2-fold higher than in untransformed cells. This is an example of manipulation of the carotenogenic pathway in eukaryotic microalgae, which can open up the possibility of enhancing the productivity of commercial carotenoids by molecular engineering.
| S-EPMC3125507 | biostudies-literature
Project description:By using stereospecifically double-labelled radioactive mevalonates it was shown that betulaprenols-6 to -9, found in the woody tissue of Betula verrucosa, each contain three biogenetically trans-isoprene residues and that the remaining residues are biogenetically cis. The results obtained with these radioactive mevalonates also indicated that the activity of isopentenyl pyrophosphate isomerase is low relative to the activity of prenyltransferase in this woody tissue. The incorporation of radioactive farnesyl pyrophosphate and radioactive geranylnerol and the lack of incorporation of radioactive geranylgeraniol into betulaprenols-6 to -9 demonstrated that they are formed by the cis-additions of isoprene residues to all-trans-farnesyl pyrophosphate.
| S-EPMC1178863 | biostudies-other
Project description:1. The incorporation of [2-(14)C,(5R)-5-(3)H(1)]mevalonic acid and [2-(14)C,5-(3)H(2)]-mevalonic acid into phytoene, phytofluene, zeta-carotene, neurosporene, alpha-, beta-, gamma- and delta-carotene and lycopene by slices of fruit from two tomato mutants (delta and tangerine) and into alpha- and beta-carotene by bean leaves has been studied. 2. In the formation of phytoene, all the pro-R-hydrogen atoms from C-5 of mevalonic acid are retained whereas two pro-S-hydrogen atoms are lost. 3. Possible mechanisms for the condensation of two molecules of all-trans-geranylgeranyl pyrophosphate are outlined. 4. In each dehydrogenation step from phytoene to the fully unsaturated carotenes, one pro-R-hydrogen atom from C-5 of mevalonic acid is lost, indicating that the sequential dehydrogenation is stereospecific and in the same sense at each step.
| S-EPMC1271218 | biostudies-other
Project description:Carotenoids are natural pigments that are indispensable to plants and humans, whereas the regulation of carotenoid biosynthesis by post-translational modification remains elusive. Here, we show that a tomato E3 ubiquitin ligase, Plastid Protein Sensing RING E3 ligase 1 (PPSR1), is responsible for the regulation of carotenoid biosynthesis. PPSR1 exhibits self-ubiquitination activity and loss of PPSR1 function leads to an increase in carotenoids in tomato fruit. PPSR1 affects the abundance of 288 proteins, including phytoene synthase 1 (PSY1), the key rate-limiting enzyme in the carotenoid biosynthetic pathway. PSY1 contains two ubiquitinated lysine residues (Lys380 and Lys406) as revealed by the global analysis and characterization of protein ubiquitination. We provide evidence that PPSR1 interacts with PSY1 precursor protein and mediates its degradation via ubiquitination, thereby affecting the steady-state level of PSY1 protein. Our findings not only uncover a regulatory mechanism for controlling carotenoid biosynthesis, but also provide a strategy for developing carotenoid-enriched horticultural crops.
| S-EPMC7713427 | biostudies-literature
Project description:Carotenoids are health-promoting plastidial isoprenoids with essential functions in plants as photoprotectants and photosynthetic pigments in chloroplasts. They also accumulate in specialized plastids named chromoplasts, providing color to non-photosynthetic tissues such as flower petals and ripe fruit. Carotenoid accumulation in chromoplasts requires specialized structures and proteins such as fibrillins (FBNs). The FBN family includes structural components of carotenoid sequestering structures in chromoplasts and members with metabolic roles in chloroplasts and other plastid types. However, the association of FBNs with carotenoids in plastids other than chromoplasts has remained unexplored. Here, we show that Arabidopsis (Arabidopsis thaliana) FBN6 interacts with phytoene synthase (PSY), the first enzyme of the carotenoid pathway. FBN6, but not FBN4 (a FBN that does not interact with PSY), enhances the activity of plant PSY (but not of the bacterial PSY crtB) in Escherichia coli cells. Overexpression of FBN6 in Nicotiana benthamiana leaves results in a higher production of phytoene, the product of PSY activity, whereas loss of FBN6 activity in Arabidopsis mutants dramatically reduces the production of carotenoids during seedling de-etiolation and after exposure to high light. Our work hence demonstrates that FBNs promote not only the accumulation of carotenoids in chromoplasts but also their biosynthesis in chloroplasts.
| S-EPMC10904322 | biostudies-literature
Project description:1. The incorporation of [2-(14)C]acetate, [2-(14)C]mevalonic acid and [2-(14)C,2-(3)H(2)]-mevalonic acid into torulene and torularhodin by Rhodotorula rubra and Rhodotorula glutinis was studied. 2. A recovery of 14.3% of the label was obtained on decarboxylation of the torularhodin biosynthesized from [2-(14)C]mevalonic acid. 3. An analysis of the (3)H/(14)C ratio in torularhodin gave a value of 9.44:8. 4. These results, obtained by different experimental techniques, show that the reactions in the conversion of the dimethyl group of isopentenyl pyrophosphate into the 16',17'-position of torularhodin must be free from randomization. A mechanism for the isomerization of isopentenyl pyrophosphate to dimethylallyl pyrophosphate is suggested.
| S-EPMC1179051 | biostudies-other
Project description:As one of the most imperative antioxidants in higher plants, carotenoids serve as accessory pigments to harvest light for photosynthesis as well as photoprotectors for plants to adapt to high light stress. Phytoene synthase (PSY) is the entry enzyme and also the major rate-limiting enzyme in the carotenoid pathway. Here, we report a dehydration-responsive element-binding protein (DREB) transcription factor member in Nicotiana tabacum K326, NtDREB-1BL1, which regulates carotenoids biosynthesis by binding to the NtPSY promoter. The NtDREB-1BL1 transcript was widely distributed in leaves by Real-time PCR. Confocal image revealed that NtDREB-1BL1 was localized in the nucleus. The chromatin immunoprecipitation (ChIP) with the qPCR technique indicated that NtDREB-1BL1 could anchor the promoter region of NtPSY. Overexpression (NtDREB-1BL1 OE) and RNA interference (NtDREB-1BL1 RNAi) of NtDREB-1BL1 were performed to evaluate its biological function in N. tabacum. Both carotenoid and chlorophyll contents increased in transgenic plants of NtDREB-1BL1 OE compared with wild-type (WT) plants, with the augment of the genes involved in carotenoid biosynthesis. In contrast, the contents of carotenoid and chlorophyll significantly decreased in transgenic plants of NtDREB-1BL1 RNAi compared to WT, along with the decline in the expression of genes related to carotenoid biosynthesis. Moreover, transgenic plants of NtDREB-1BL1 OE exhibited enhanced tolerance under drought stress, with the weakened tolerance of drought stress in transgenic plants of NtDREB-1BL1 RNAi. In conclusion, our results illustrated the new role of transcription factor NtDREB-1BL1 in improving carotenoid biosynthesis through regulating NtPSY expression.
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Project description:Carotenoids are key for plants to optimize carbon fixing using the energy of sunlight. They contribute to light harvesting but also channel energy away from chlorophylls to protect the photosynthetic apparatus from excess light. Phytochrome-mediated light signals are major cues regulating carotenoid biosynthesis in plants, but we still lack fundamental knowledge on the components of this signaling pathway. Here we show that phytochrome-interacting factor 1 (PIF1) and other transcription factors of the phytochrome-interacting factor (PIF) family down-regulate the accumulation of carotenoids by specifically repressing the gene encoding phytoene synthase (PSY), the main rate-determining enzyme of the pathway. Both in vitro and in vivo evidence demonstrate that PIF1 directly binds to the promoter of the PSY gene, and that this binding results in repression of PSY expression. Light-triggered degradation of PIFs after interaction with photoactivated phytochromes during deetiolation results in a rapid derepression of PSY gene expression and a burst in the production of carotenoids in coordination with chlorophyll biosynthesis and chloroplast development for an optimal transition to photosynthetic metabolism. Our results also suggest a role for PIF1 and other PIFs in transducing light signals to regulate PSY gene expression and carotenoid accumulation during daily cycles of light and dark in mature plants.
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