Peter Beyer

University of Freiburg, Freiburg, Baden-Württemberg, Germany

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Publications (102)453.52 Total impact

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    ABSTRACT: The whole-genome transcriptomic cold stress response of the moss Physcomitrella patens was analyzed and correlated with phenotypic and metabolic changes. Based on time-series microarray experiments and quantitative real-time polymerase chain reaction, we characterized the transcriptomic changes related to early stress signaling and the initiation of cold acclimation. Transcription-associated protein (TAP)-encoding genes of P. patens and Arabidopsis thaliana were classified using generalized linear models. Physiologi-cal responses were monitored with pulse-amplitude-modulated fluorometry, high-perfor-mance liquid chromatography and targeted high-performance mass spectrometry. The transcript levels of 3220 genes were significantly affected by cold. Comparative classifi-cation revealed a global specialization of TAP families, a transcript accumulation of transcrip-tional regulators of the stimulus/stress response and a transcript decline of developmental regulators. Although transcripts of the intermediate to later response are from evolutionarily conserved genes, the early response is dominated by species-specific genes. These orphan genes may encode as yet unknown acclimation processes.
    New Phytologist 09/2014; · 6.74 Impact Factor
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    ABSTRACT: Crocus sativus stigmas are the source of the saffron spice and accumulate the apocarotenoids crocetin, crocins, picrocrocin, and safranal, responsible for its color, taste, and aroma. Through deep transcriptome sequencing, we identified a novel dioxygenase, carotenoid cleavage dioxygenase 2 (CCD2), expressed early during stigma development and closely related to, but distinct from, the CCD1 dioxygenase family. CCD2 is the only identified member of a novel CCD clade, presents the structural features of a bona fide CCD, and is able to cleave zeaxanthin, the presumed precursor of saffron apocarotenoids, both in Escherichia coli and in maize endosperm. The cleavage products, identified through high-resolution mass spectrometry and comigration with authentic standards, are crocetin dialdehyde and crocetin, respectively. In vitro assays show that CCD2 cleaves sequentially the 7,8 and 7',8' double bonds adjacent to a 3-OH-β-ionone ring and that the conversion of zeaxanthin to crocetin dialdehyde proceeds via the C30 intermediate 3-OH-β-apo-8'-carotenal. In contrast, zeaxanthin cleavage dioxygenase (ZCD), an enzyme previously claimed to mediate crocetin formation, did not cleave zeaxanthin or 3-OH-β-apo-8'-carotenal in the test systems used. Sequence comparison and structure prediction suggest that ZCD is an N-truncated CCD4 form, lacking one blade of the β-propeller structure conserved in all CCDs. These results constitute strong evidence that CCD2 catalyzes the first dedicated step in crocin biosynthesis. Similar to CCD1, CCD2 has a cytoplasmic localization, suggesting that it may cleave carotenoids localized in the chromoplast outer envelope.
    Proceedings of the National Academy of Sciences 08/2014; 5. · 9.81 Impact Factor
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    ABSTRACT: The plastid terminal oxidase PTOX catalyzes the oxidation of plastoquinol (PQH2) coupled with the reduction of oxygen to water. In vivo PTOX is attached to the thylakoid membrane. PTOX is important for plastid development and carotenoid biosynthesis, and its role in photosynthesis is controversially discussed. To analyze PTOX activity in photosynthetic electron transport recombinant purified PTOX fused to the maltose-binding protein was added to photosystem II-enriched membrane fragments. These membrane fragments contain the plastoquinone (PQ) pool as verified by thermoluminescence. Experimental evidence for PTOX oxidizing PQH2 is demonstrated by following chlorophyll fluorescence induction. Addition of PTOX to photosystem II-enriched membrane fragments led to a slower rise, a lower level of the maximal fluorescence and an acceleration of the fluorescence decay. This effect was only observed at low light intensities indicating that PTOX cannot compete efficiently with the reduction of the PQ pool by photosystem II at higher light intensities. PTOX attached tightly to the membranes since it was only partly removable by membrane washings. Divalent cations enhanced the effect of PTOX on chlorophyll fluorescence compared to NaCl most likely because they increase connectivity between photosystem II centers and the size of the PQ pool. Using single turnover flashes, it was shown that the level of reactive oxygen species, generated by PTOX in a side reaction, increased when the spacing between subsequent double flashes were enlarged. This shows that PTOX generates reactive oxygen species under limited substrate availability.
    Biochimica et biophysica acta. 08/2014;
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    ABSTRACT: The typically intense carotenoid accumulation in cultivated orange-rooted carrots (Daucus carota) is determined by a high protein abundance of the rate-limiting enzyme for carotenoid biosynthesis, phytoene synthase (PSY), as compared with white-rooted cultivars. However, in contrast to other carotenoid accumulating systems, orange carrots are characterized by unusually high levels of α-carotene in addition to β-carotene. We found similarly increased α-carotene levels in leaves of orange carrots compared with white-rooted cultivars. This has also been observed in the Arabidopsis thaliana lut5 mutant carrying a defective carotene hydroxylase CYP97A3 gene. In fact, overexpression of CYP97A3 in orange carrots restored leaf carotenoid patterns almost to those found in white-rooted cultivars and strongly reduced α-carotene levels in the roots. Unexpectedly, this was accompanied by a 30 to 50% reduction in total root carotenoids and correlated with reduced PSY protein levels while PSY expression was unchanged. This suggests a negative feedback emerging from carotenoid metabolites determining PSY protein levels and, thus, total carotenoid flux. Furthermore, we identified a deficient CYP97A3 allele containing a frame-shift insertion in orange carrots. Association mapping analysis using a large carrot population revealed a significant association of this polymorphism with both α-carotene content and the α-/β-carotene ratio and explained a large proportion of the observed variation in carrots.
    The Plant cell. 05/2014;
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    ABSTRACT: The plastid terminal oxidase (PTOX) is a plastohydroquinone:oxygen oxidoreductase that shares structural similarities with alternative oxidases (AOX). Multiple roles have been attributed to PTOX, such as involvement in carotene desaturation, a safety valve function, participation in the processes of chlororespiration and setting the redox poise for cyclic electron transport. We have investigated a homogenously pure MBP fusion of PTOX. The protein forms a homo-tetrameric complex containing 2 Fe per monomer and is very specific for the plastoquinone head-group. The reaction kinetics were investigated in a soluble monophasic system using chemically reduced decyl-plastoquinone (DPQ) as the model substrate and, in addition, in a biphasic (liposomal) system in which DPQ was reduced with DT-diaphorase. While PTOX did not detectably produce reactive oxygen species in the monophasic system, their formation was observed by room temperature EPR in the biphasic system in a [DPQH2] and pH-dependent manner. This is probably the result of the higher concentration of DPQ achieved within the partial volume of the lipid bilayer and a higher Km observed with PTOX-membrane associates which is≈47mM compared to the monophasic system where a Km of≈74μM was determined. With liposomes and at the basic stromal pH of photosynthetically active chloroplasts, PTOX was antioxidant at low [DPQH2] gaining prooxidant properties with increasing quinol concentrations. It is concluded that in vivo, PTOX can act as a safety valve when the steady state [PQH2] is low while a certain amount of ROS is formed at high light intensities.
    Biochimica et Biophysica Acta 04/2014; · 4.66 Impact Factor
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    ABSTRACT: Strigolactones are phytohormones synthesized from carotenoids via a stereospecific pathway involving the carotenoid cleavage dioxygenases 7 (CCD7) and 8. CCD7 cleaves 9-cis-β-carotene to form a supposedly 9-cis-configured β-apo-10'-carotenal. CCD8 converts this intermediate through a combination of yet undetermined reactions into the strigolactone-like compound carlactone. Here, we investigated the substrate and stereo-specificity of the Arabidopsis and pea CCD7 and determined the stereo-configuration of the β-apo-10'-carotenal intermediate by using Nuclear Magnetic Resonance Spectroscopy. Our data unequivocally demonstrate the 9-cis-configuration of the intermediate. Both CCD7s cleave different 9-cis-carotenoids, yielding hydroxylated 9-cis-apo-10'-carotenals that may lead to hydroxylated carlactones, but show highest affinity for 9-cis-β-carotene.
    FEBS letters 03/2014; · 3.54 Impact Factor
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    ABSTRACT: The plastid terminal oxidase (PTOX) is a plastohydroquinone:oxygen oxidoreductase that shares structural similarities with alternative oxidases (AOX). Multiple roles have been attributed to PTOX, such as involvement in carotene desaturation, a safety valve function, participation in the processes of chlororespiration and setting the redox poise for cyclic electron transport. We have investigated a homogenously pure MBP fusion of PTOX. The protein forms a homo-tetrameric complex containing 2 Fe per monomer and is very specific for the plastoquinone head-group. The reaction kinetics were investigated in a soluble monophasic system using chemically reduced decyl-plastoquinone (DPQ) as the model substrate and, in addition, in a biphasic (liposomal) system in which DPQ was reduced with DT-diaphorase. While PTOX did not detectably produce reactive oxygen species in the monophasic system, their formation was observed by room temperature EPR in the biphasic system in a [DPQH2] and pH-dependent manner. This is probably the result of the higher concentration of DPQ achieved within the partial volume of the lipid bilayer and a higher Km observed with PTOX-membrane associates which is ≈ 47 mM compared to the monophasic system where a Km of ≈ 74 μM was determined. With liposomes and at the basic stromal pH of photosynthetically active chloroplasts, PTOX was antioxidant at low [DPQH2] gaining prooxidant properties with increasing quinol concentrations. It is concluded that in vivo, PTOX can act as a safety valve when the steady state [PQH2] is low while a certain amount of ROS is formed at high light intensities.
    Biochimica et Biophysica Acta (BBA) - Bioenergetics. 01/2014;
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    ABSTRACT: The biosynthetic processes leading to many of the isoprenoid volatiles released by tomato fruits are still unknown, though previous reports suggested a clear correlation with the carotenoids contained within the fruit. In this study, we investigated the activity of the tomato (Solanum lycopersicum) carotenoid cleavage dioxygenase (SlCCD1B), which is highly expressed in fruits, and of its homolog SlCCD1A. Using in vitro assays performed with purified recombinant enzymes and by analyzing products formed by the two enzymes in carotene-accumulating Escherichia coli strains, we demonstrate that SlCCD1A and, to a larger extent, SlCCD1B, have a very relaxed specificity for both substrate and cleavage site, mediating the oxidative cleavage of cis- and all-trans-carotenoids as well as of different apocarotenoids at many more double bonds than previously reported. This activity gives rise to a plenitude of volatiles, mono-apocarotenoids and dialdehyde products, including cis-pseudoionone, neral, geranial, and farnesylacetone. Our results provide a direct evidence for a carotenoid origin of these compounds and point to CCD1s as the enzymes catalyzing the formation of the vast majority of tomato isoprenoid volatiles, many of which are aroma constituents.
    FEBS Open Bio. 01/2014;
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    ABSTRACT: The constitutive expression of the bacterial carotene desaturase (CRTI) in Arabidopsis thaliana leads to increased susceptibility of leaves to light-induced damage. Changes in the photosynthetic electron transport chain rather than alterations of the carotenoid composition in the antenna were responsible for the increased photoinhibition. A much higher level of superoxide/hydrogen peroxide was generated in the light in thylakoid membranes from the CRTI expressing lines than in wild-type while the level of singlet oxygen generation remained unchanged. The increase in reactive oxygen species was related to the activity of plastid terminal oxidase (PTOX) since their generation was inhibited by the PTOX-inhibitor octyl gallate, and since the protein level of PTOX was increased in the CRTI-expressing lines. Furthermore, cyclic electron flow was suppressed in these lines. We propose that PTOX competes efficiently with cyclic electron flow for plastoquinol in the CRTI-expressing lines and that it plays a crucial role in the control of the reduction state of the plastoquinone pool.
    Biochimica et Biophysica Acta 12/2013; · 4.66 Impact Factor
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    ABSTRACT: Oxidative cleavage of carotenoids and peroxidation of lipids lead to apocarotenals and aliphatic aldehydes called alkanals, which can react with vitally important compounds, promoting cytotoxicity. While many enzymes have been reported to deactivate alkanals by converting them into fatty acids, little is known about mechanisms employed to detoxify apocarotenals or enzymes acting on them. Cyanobacteria and other photosynthetic organisms have to cope with both classes of aldehydes. Here, we report that the Synechocystis enzyme SynAlh1, encoded by the ORF slr0091, is an aldehyde dehydrogenase mediating the oxidation of both apocarotenals and alkanals into the corresponding acids. Using crude lysate of SynAlh1 expressing Escherichia coli cells, we show that it converts a wide range of apocarotenals and alkanals, with a preference for apocarotenals with defined chain lengths. As suggested by in vitro incubations and using engineered retinal-forming Escherichia coli cells, retinal is not a substrate for SynAlh1, making an involvement in the supposed Synechocystis retinoid metabolism unlikely. Indicating a role in stress response, the transcript level of SynAlh1 is induced by high-light and cold treatment, and the corresponding gene is a constituent of a stress-related operon. The assumption on the function of SynAlh is further supported by the surprisingly high homology to human and plant ALDHs that have been assigned to aldehyde detoxification. SynAlh1 is the first ALDH shown to form both apocarotenoic and fatty acids. This dual function indicates that eukaryotic homologs may also be involved in apocarotenals metabolism, a function that has not been considered so far. This article is protected by copyright. All rights reserved.
    FEBS Journal 06/2013; · 4.25 Impact Factor
  • Qiuju Yu, Peter Beyer
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    ABSTRACT: Lycopene cyclases responsible for the formation of ε-ionone rings (LCYe) mark a plant-specific bifurcation of carotenogenesis. We investigated purified rice LCYe (OsLCYe) in a liposome-based biphasic assay system. OsLCYe depends on reduced flavin cofactors stabilizing a transient state formed during the non-redox cyclization reaction. In contrast to OsLCYb, OsLCYe produces predominantly monocyclic products and monocyclic carotene intermediates are not suitable substrates. Determination of the OsLCYe reaction specificities and the combined use of OsLCYb allow the characterization of the reaction sequence leading to heterocyclic carotenoids. It was also found that 5-cis-lycopene, which was thought to be decisive for ε-cyclization, was not involved in the reaction, with OsLCYe acting as an exclusion filter for this naturally occurring isomer.
    FEBS letters 07/2012; 586(19):3415-20. · 3.54 Impact Factor
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    ABSTRACT: Strigolactones, phytohormones with diverse signaling activities, have a common structure consisting of two lactones connected by an enol-ether bridge. Strigolactones derive from carotenoids via a pathway involving the carotenoid cleavage dioxygenases 7 and 8 (CCD7 and CCD8) and the iron-binding protein D27. We show that D27 is a β-carotene isomerase that converts all-trans-β-carotene into 9-cis-β-carotene, which is cleaved by CCD7 into a 9-cis-configured aldehyde. CCD8 incorporates three oxygens into 9-cis-β-apo-10'-carotenal and performs molecular rearrangement, linking carotenoids with strigolactones and producing carlactone, a compound with strigolactone-like biological activities. Knowledge of the structure of carlactone will be crucial for understanding the biology of strigolactones and may have applications in combating parasitic weeds.
    Science 03/2012; 335(6074):1348-51. · 31.20 Impact Factor
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    ABSTRACT: CRTI-type phytoene desaturases prevailing in bacteria and fungi can form lycopene directly from phytoene while plants employ two distinct desaturases and two cis-tans isomerases for the same purpose. This property renders CRTI a valuable gene to engineer provitamin A-formation to help combat vitamin A malnutrition, such as with Golden Rice. To understand the biochemical processes involved, recombinant CRTI was produced and obtained in homogeneous form that shows high enzymatic activity with the lipophilic substrate phytoene contained in phosphatidyl-choline (PC) liposome membranes. The first crystal structure of apo-CRTI reveals that CRTI belongs to the flavoprotein superfamily comprising protoporphyrinogen IX oxidoreductase and monoamine oxidase. CRTI is a membrane-peripheral oxidoreductase which utilizes FAD as the sole redox-active cofactor. Oxygen, replaceable by quinones in its absence, is needed as the terminal electron acceptor. FAD, besides its catalytic role also displays a structural function by enabling the formation of enzymatically active CRTI membrane associates. Under anaerobic conditions the enzyme can act as a carotene cis-trans isomerase. In silico-docking experiments yielded information on substrate binding sites, potential catalytic residues and is in favor of single half-site recognition of the symmetrical C(40) hydrocarbon substrate.
    PLoS ONE 01/2012; 7(6):e39550. · 3.53 Impact Factor
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    ABSTRACT: The carotene cis-trans isomerase CRTISO is a constituent of the carotene desaturation pathway as evolved in cyanobacteria and prevailing in plants, in which a tetra-cis-lycopene species, termed prolycopene, is formed. CRTISO, an evolutionary descendant of the bacterial carotene desaturase CRTI, catalyzes the cis-to-trans isomerization reactions leading to all-trans-lycopene, the substrate for the subsequent lycopene cyclization to form all-trans-α/β-carotene. CRTISO and CRTI share a dinucleotide binding motif at the N terminus. Here we report that this site is occupied by FAD in CRTISO. The reduced form of this cofactor catalyzes a reaction not involving net redox changes. Results obtained with C(1)- and C(5)-deaza-FAD suggest mechanistic similarities with type II isopentenyl diphosphate: dimethylallyl diphosphate isomerase (IDI-2). CRTISO, together with lycopene cyclase CRTY and IDI-2, thus represents the third enzyme in isoprenoid metabolism belonging to the class of non-redox enzymes depending on reduced flavin for activity. The regional specificity and the kinetics of the isomerization reaction were investigated in vitro using purified enzyme and biphasic liposome-based systems carrying specific cis-configured lycopene species as substrates. The reaction proceeded from cis to trans, recognizing half-sides of the symmetrical prolycopene and was accompanied by one trans-to-cis isomerization step specific for the C(5)-C(6) double bond. Rice lycopene β-cyclase (OsLCY-b), when additionally introduced into the biphasic in vitro system used, was found to be stereospecific for all-trans-lycopene and allowed the CRTISO reaction to proceed toward completion by modifying the thermodynamics of the overall reaction.
    Journal of Biological Chemistry 03/2011; 286(10):8666-8676. · 4.65 Impact Factor
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    ABSTRACT: The carotene cis-trans isomerase CRTISO is a constituent of the carotene desaturation pathway as evolved in cyanobacteria and prevailing in plants, in which a tetra-cis-lycopene species, termed prolycopene, is formed. CRTISO, an evolutionary descendant of the bacterial carotene desaturase CRTI, catalyzes the cis-to-trans isomerization reactions leading to all-trans-lycopene, the substrate for the subsequent lycopene cyclization to form all-trans-α/β-carotene. CRTISO and CRTI share a dinucleotide binding motif at the N terminus. Here we report that this site is occupied by FAD in CRTISO. The reduced form of this cofactor catalyzes a reaction not involving net redox changes. Results obtained with C(1)- and C(5)-deaza-FAD suggest mechanistic similarities with type II isopentenyl diphosphate: dimethylallyl diphosphate isomerase (IDI-2). CRTISO, together with lycopene cyclase CRTY and IDI-2, thus represents the third enzyme in isoprenoid metabolism belonging to the class of non-redox enzymes depending on reduced flavin for activity. The regional specificity and the kinetics of the isomerization reaction were investigated in vitro using purified enzyme and biphasic liposome-based systems carrying specific cis-configured lycopene species as substrates. The reaction proceeded from cis to trans, recognizing half-sides of the symmetrical prolycopene and was accompanied by one trans-to-cis isomerization step specific for the C(5)-C(6) double bond. Rice lycopene β-cyclase (OsLCY-b), when additionally introduced into the biphasic in vitro system used, was found to be stereospecific for all-trans-lycopene and allowed the CRTISO reaction to proceed toward completion by modifying the thermodynamics of the overall reaction.
    Journal of Biological Chemistry 01/2011; 286(10):8666-76. · 4.65 Impact Factor
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    Peter Beyer
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    ABSTRACT: Micronutrients are essential for a healthy life. Humans do not produce micronutrients, and hence they must obtain them through the foodchain. Staple crops are the predominant food source of mankind, but need to be complemented by other foodstuffs because they are generally deficient in one or the other micronutrient. Breeding for micronutrient-dense crops is not always a viable option because of the absence of genetic variability for the desired trait. Moreover, sterility issues and the complex genetic makeup of some crop plants make them unamenable to conventional breeding. In these cases, genetic modification remains the only viable option. The tools to produce a number of micronutrients in staple crops have recently become available thanks to the identification of the genes involved in the corresponding biochemical pathways at an unprecedented rate. Discarding genetic modification as a viable option is definitely not in the interest of human wellbeing.
    New Biotechnology 11/2010; 27(5):478-81. · 1.71 Impact Factor
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    ABSTRACT: Vitamin A deficiency is a public health problem in a large number of countries. Biofortification of major staple crops (wheat [Triticum aestivum], rice [Oryza sativa], maize [Zea mays], and potato [Solanum tuberosum]) with β-carotene has the potential to alleviate this nutritional problem. Previously, we engineered transgenic "Golden" potato tubers overexpressing three bacterial genes for β-carotene synthesis (CrtB, CrtI, and CrtY, encoding phytoene synthase, phytoene desaturase, and lycopene β-cyclase, respectively) and accumulating the highest amount of β-carotene in the four aforementioned crops. Here, we report the systematic quantitation of carotenoid metabolites and transcripts in 24 lines carrying six different transgene combinations under the control of the 35S and Patatin (Pat) promoters. Low levels of B-I expression are sufficient for interfering with leaf carotenogenesis, but not for β-carotene accumulation in tubers and calli, which requires high expression levels of all three genes under the control of the Pat promoter. Tubers expressing the B-I transgenes show large perturbations in the transcription of endogenous carotenoid genes, with only minor changes in carotenoid content, while the opposite phenotype (low levels of transcriptional perturbation and high carotenoid levels) is observed in Golden (Y-B-I) tubers. We used hierarchical clustering and pairwise correlation analysis, together with a new method for network correlation analysis, developed for this purpose, to assess the perturbations in transcript and metabolite levels in transgenic leaves and tubers. Through a "guilt-by-profiling" approach, we identified several endogenous genes for carotenoid biosynthesis likely to play a key regulatory role in Golden tubers, which are candidates for manipulations aimed at the further optimization of tuber carotenoid content.
    Plant physiology 10/2010; 154(2):899-912. · 6.56 Impact Factor
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    ABSTRACT: Abiotic stress stimuli induce the increased synthesis of abscisic acid (ABA), which is generated through the cleavage of xanthophyll precursors. To cope with the increased xanthophyll demand, maize and rice contain a third stress-induced gene copy, coding for phytoene synthase (PSY), which catalyzes the first carotenoid-specific reaction in the pathway. To investigate whether this specific response extends beyond the Poaceae, cassava was analyzed, an important tropical crop known for its drought tolerance. We also found three PSY genes in cassava, one of which (MePSY3) forms a separate branch with the stress-specific Poaceae homologs. However, MePSY3 transcripts were virtually absent in all tissues investigated and did not change upon abiotic stress treatment. In contrast, the two remaining PSY genes contributed differentially to carotenoid biosynthesis in leaves, roots, and flower organs and responded towards drought and salt-stress conditions. Detailed analyses of PSY and 9-cis-epoxycarotenoid cleavage dioxygenase (MeNCED) expression and resulting ABA levels revealed MePSY1 as the main stress-responsive paralog. In the presence of high carotenoid levels in leaves, MePSY1 appeared to support, but not to be rate-limiting for ABA formation; MeNCED represented the main driver. The inverse situation was found in roots where carotenoid levels are low. Moreover, ABA formation and the relative induction kinetics showed discrimination between drought and salt stress. Compared to rice as a drought-intolerant species, the drought response in cassava followed a different kinetic regime. The difference is thought to represent a component contributing to the large differences in the adaptation towards water supply.
    Planta 10/2010; 232(5):1251-62. · 3.38 Impact Factor
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    ABSTRACT: Cassava (Manihot esculenta) is an important staple crop, especially in the arid tropics. Because roots of commercial cassava cultivars contain a limited amount of provitamin A carotenoids, both conventional breeding and genetic modification are being applied to increase their production and accumulation to fight vitamin A deficiency disorders. We show here that an allelic polymorphism in one of the two expressed phytoene synthase (PSY) genes is capable of enhancing the flux of carbon through carotenogenesis, thus leading to the accumulation of colored provitamin A carotenoids in storage roots. A single nucleotide polymorphism present only in yellow-rooted cultivars cosegregates with colored roots in a breeding pedigree. The resulting amino acid exchange in a highly conserved region of PSY provides increased catalytic activity in vitro and is able to increase carotenoid production in recombinant yeast and Escherichia coli cells. Consequently, cassava plants overexpressing a PSY transgene produce yellow-fleshed, high-carotenoid roots. This newly characterized PSY allele provides means to improve cassava provitamin A content in cassava roots through both breeding and genetic modification.
    The Plant Cell 10/2010; 22(10):3348-56. · 9.25 Impact Factor
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    ABSTRACT: Carotenoids are converted by carotenoid cleavage dioxygenases that catalyze oxidative cleavage reactions leading to apocarotenoids. However, apocarotenoids can also be further truncated by some members of this enzyme family. The plant carotenoid cleavage dioxygenase 1 (CCD1) subfamily is known to degrade both carotenoids and apocarotenoids in vitro, leading to different volatile compounds. In this study, we investigated the impact of the rice CCD1 (OsCCD1) on the pigmentation of Golden Rice 2 (GR2), a genetically modified rice variety accumulating carotenoids in the endosperm. For this purpose, the corresponding cDNA was introduced into the rice genome under the control of an endosperm-specific promoter in sense and anti-sense orientations. Despite high expression levels of OsCCD1 in sense plants, pigment analysis revealed carotenoid levels and patterns comparable to those of GR2, pleading against carotenoids as substrates in rice endosperm. In support, similar carotenoid contents were determined in anti-sense plants. To check whether OsCCD1 overexpressed in GR2 endosperm is active, in vitro assays were performed with apocarotenoid substrates. HPLC analysis confirmed the cleavage activity of introduced OsCCD1. Our data indicate that apocarotenoids rather than carotenoids are the substrates of OsCCD1 in planta.
    Planta 08/2010; 232(3):691-9. · 3.38 Impact Factor

Publication Stats

4k Citations
453.52 Total Impact Points

Institutions

  • 1980–2014
    • University of Freiburg
      • • Faculty of Biology
      • • Institute of Biology II
      • • Institute of Biology I
      Freiburg, Baden-Württemberg, Germany
  • 2006–2007
    • ENEA
      Roma, Latium, Italy
  • 2003
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland
  • 1991–1994
    • University of California, Berkeley
      • Department of Chemistry
      Berkeley, MO, United States