Paul Christou

Catalan Institution for Research and Advanced Studies, Barcino, Catalonia, Spain

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Publications (223)1180.09 Total impact

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    ABSTRACT: Plant metabolic pathways are complex and often feature multiple levels of regulation. Until recently, metabolic engineering in plants relied on the laborious testing of ad hoc modifications to achieve desirable changes in the metabolic profile. However, technological advances in data mining, modeling, multigene engineering and genome editing are now taking away much of the guesswork by allowing the impact of modifications to be predicted more accurately. In this review we discuss recent developments in knowledge-based metabolic engineering strategies, that is the gathering and mining of genomic, transcriptomic, proteomic and metabolomic data to generate models of metabolic pathways that help to define and refine optimal intervention strategies. Copyright © 2014 Elsevier Ltd. All rights reserved.
    Current Opinion in Biotechnology 11/2014; · 8.04 Impact Factor
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    Maite Sabalza, Paul Christou, Teresa Capell
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    ABSTRACT: Molecular pharming is a cost-effective platform for the production of recombinant proteins in plants. Although the biopharmaceutical industry still relies on a small number of standardized fermentation-based technologies for the production of recombinant proteins there is now a greater awareness of the advantages of molecular pharming particularly in niche markets. Here we discuss some of the technical, economic and regulatory barriers that constrain the clinical development and commercialization of plant-derived pharmaceutical proteins. We also discuss strategies to increase productivity and product quality/homogeneity. The advantages of whole plants should be welcomed by the industry because this will help to reduce the cost of goods and therefore expand the biopharmaceutical market into untapped sectors.
    Biotechnology Letters 07/2014; · 1.74 Impact Factor
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    E Vamvaka, R M Twyman, P Christou, T Capell
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    ABSTRACT: The population of sub-Saharan Africa is at risk from multiple, poverty-related endemic diseases. HIV and malaria are the most prevalent, but they disproportionately affect different groups of people, i.e. HIV predominantly affects sexually-active adults whereas malaria has a greater impact on children and pregnant women. Nevertheless, there is a significant geographical and epidemiological overlap which results in bidirectional and synergistic interactions with important consequences for public health. The immunosuppressive effects of HIV increase the risk of infection when individuals are exposed to malaria parasites and also the severity of malaria symptoms. Similarly, acute malaria can induce a temporary increase in the HIV viral load. HIV is associated with a wide range of opportunistic infections that can be misdiagnosed as malaria, resulting in the wasteful misuse of antimalarial drugs and a failure to address the genuine cause of the disease. There is also a cumulative risk of toxicity when antiretroviral and antimalarial drugs are given to the same patients. Synergistic approaches involving the control of malaria as a strategy to fight HIV/AIDS and vice versa are therefore needed in co-endemic areas. Plant biotechnology has emerged as a promising approach to tackle poverty-related diseases because plant-derived drugs and vaccines can be produced inexpensively in developing countries and may be distributed using agricultural infrastructure without the need for a cold chain. Here we explore some of the potential contributions of plant biotechnology and its integration into broader multidisciplinary public health programs to combat the two diseases in developing countries.
    Biotechnology advances 03/2014; · 8.91 Impact Factor
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    ABSTRACT: Metabolic engineering can be used to modulate endogenous metabolic pathways in plants or introduce new metabolic capabilities in order to increase the production of a desirable compound or reduce the accumulation of an undesirable one. In practice, there are several major challenges that need to be overcome, such as gaining enough knowledge about the endogenous pathways to understand the best intervention points, identifying and sourcing the most suitable metabolic genes, expressing those genes in such a way as to produce a functional enzyme in a heterologous background, and, finally, achieving the accumulation of target compounds without harming the host plant. This article discusses the strategies that have been developed to engineer complex metabolic pathways in plants, focusing on recent technological developments that allow the most significant bottlenecks to be overcome. Expected final online publication date for the Annual Review of Plant Biology Volume 65 is April 29, 2014. Please see for revised estimates.
    Annual Review of Plant Biology 02/2014; · 18.71 Impact Factor
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    ABSTRACT: The do-it-yourself patent search is a useful alternative to professional patent analysis particularly in the context of publicly funded projects where funds for IP activities may be limited. As a case study, we analysed patents related to the engineering of terpenoid indole alkaloid (TIA) metabolism in plants. We developed a focused search strategy to remove redundancy and reduce the workload without missing important and relevant patents. This resulted in the identification of approximately 50 key patents associated with TIA metabolic engineering in plants, which could form the basis of a more detailed freedom-to-operate analysis. The structural elements of this search strategy could easily be transferred to other contexts, making it a useful generic model for publicly funded research projects.
    Plant Biotechnology Journal 02/2014; 12(2):117-34. · 6.28 Impact Factor
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    ABSTRACT: Rice endosperm is devoid of carotenoids because the initial biosynthetic steps are absent. The early carotenogenesis reactions were constituted through co-transformation of endosperm-derived rice callus with phytoene synthase and phytoene desaturase transgenes. Subsequent steps in the pathway such as cyclization and hydroxylation reactions were catalyzed by endogenous rice enzymes in the endosperm. The carotenoid pathway was extended further by including a bacterial ketolase gene able to form astaxanthin, a high value carotenoid which is not a typical plant carotenoid. In addition to astaxanthin and precursors, a carotenoid accumulated in the transgenic callus which did not fit into the pathway to astaxanthin. This was subsequently identified as 4-keto-α-carotene by HPLC co-chromatography, chemical modification, mass spectrometry and the reconstruction of its biosynthesis pathway in Escherichia coli. We postulate that this keto carotenoid is formed from α-carotene which accumulates by combined reactions of the heterologous gene products and endogenous rice endosperm cyclization reactions.
    Phytochemistry 01/2014; · 3.35 Impact Factor
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    ABSTRACT: The food production and processing value chain is under pressure from all sides—increasing demand driven by a growing and more affluent population; dwindling resources caused by urbanization, land erosion, pollution and competing agriculture such as biofuels; and increasing constraints on production methods driven by consumers and regulators demanding higher quality, reduced chemical use, and most of all environmentally beneficial practices ‘from farm to fork’. This pressure can only be addressed by developing efficient and sustainable agricultural practices that are harmonized throughout the value chain, so that renewable resources can be exploited without damaging the environment. Bridges must, therefore, be built between the diverse areas within the food production and processing value chain, including bridges between different stages of production, between currently unlinked agronomic practices, and between the different levels and areas of research to achieve joined-up thinking within the industry, so that the wider impact of different technologies, practices and materials on productivity and sustainability is understood at the local, regional, national and global scales. In this article, we consider the challenges at different stages and levels of the value chain and how new technologies and strategies could be used to build bridges and achieve more sustainable food/feed production in the future.
    Molecular Breeding 12/2013; · 2.28 Impact Factor
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    ABSTRACT: We have developed an assay based on rice embryogenic callus for the rapid functional characterization of metabolic genes. We validated the assay using a selection of well-characterized genes with known functions in the carotenoid biosynthesis pathway, allowing the rapid visual screening of callus phenotypes based on tissue color. We were then able to use the system to identify the functions of two uncharacterized genes: a chemically-synthesized β-carotene ketolase gene optimized for maize codon usage; and a wild-type Arabidopsis thaliana ortholog of the cauliflower Orange gene. In contrast to previous reports, we found that the wild-type Orange allele was sufficient to induce chromoplast differentiation. We also found that chromoplast differentiation could be induced by increasing the availability of precursors and thus driving flux through the pathway, even in the absence of Orange. Remarkably, we found that diverse endosperm-specific promoters were highly active in rice callus despite their restricted activity in mature plants. Our callus system provides a unique opportunity to predict the impact of metabolic engineering in complex pathways and provides a starting point for quantitative modeling and the rational design of engineering strategies using synthetic biology. We discuss the impact of our data on the analysis and engineering of the carotenoid biosynthesis pathway. This article is protected by copyright. All rights reserved.
    The Plant Journal 11/2013; · 6.82 Impact Factor
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    ABSTRACT: Over the last two decades, many carotenogenic genes have been cloned and used to generate metabolically-engineered plants producing higher levels of carotenoids. However, comparatively little is known about the regulation of endogenous carotenogenic genes in higher plants, and this restricts our ability to predict how engineered plants will perform in terms of carotenoid content and composition. During petal development in the Great Yellow Gentian (Gentiana lutea), carotenoid accumulation, the formation of chromoplasts and the upregulation of several carotenogenic genes are temporally coordinated. We investigated the regulatory mechanisms responsible for this coordinated expression by isolating five G. lutea carotenogenic gene (GlPDS, GlZDS, GlLYCB, GlBCH and GlLYCE) promoters by inverse PCR. Each promoter was sufficient for developmentally-regulated expression of the gusA reporter gene following transient expression in tomato (Solanum lycopersicum cv. Micro-Tom). Interestingly, the GlLYCB and GlBCH promoters drove high levels of gusA expression in chromoplast-containing mature green fruits, but low levels in chloroplast-containing immature green fruits, indicating a strict correlation between promoter activity, tomato fruit development and chromoplast differentiation. As well as core promoter elements such as TATA and CAAT boxes, all five promoters together with previously characterized GlZEP promoter contained three common cis-regulatory motifs involved in the response to methyl jasmonate (CGTCA) and ethylene (ATCTA), and required for endosperm expression (Skn-1_motif, GTCAT). These shared common cis-acting elements may represent binding sites for transcription factors responsible for co-regulation. Our data provide insight into the regulatory basis of the coordinated upregulation of carotenogenic gene expression during flower development in G. lutea.
    Physiologia Plantarum 11/2013; · 3.26 Impact Factor
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    ABSTRACT: The present review compiles positive MS fragmentation data of selected carotenoids obtained using various ionization techniques and matrices. In addition, new experimental data from the analysis of carotenoids in transgenic maize and rice callus are provided. Several carotenes and oxygen-functionalized carotenoids containing epoxy, hydroxyl, and ketone groups were ionized by atmospheric pressure chemical ionization (APCI)-tandem mass spectrometry (MS/MS) in positive ion mode. Thus, on the basis of the information obtained from the literature and our own experiments, we identified characteristic carotenoid ions that can be associated to functional groups in the structures of these compounds. In addition, pigments with a very similar structure were differentiated through comparison of the intensities of their fragments. The data provide a basis for the structural elucidation of carotenoids by mass spectrometry (MS). © 2013 Wiley Periodicals, Inc. Mass Spec Rev. 9999: 1-20, 2013.
    Mass Spectrometry Reviews 10/2013; · 8.05 Impact Factor
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    ABSTRACT: The biofortification of staple crops with vitamins is an attractive strategy to increase the nutritional quality of human food, particularly in areas where the population subsists on a cereal-based diet. Unlike other approaches, biofortification is sustainable and does not require anything more than a standard food-distribution infrastructure. The health-promoting effects of vitamins depend on overall intake and bioavailability, the latter influenced by food processing, absorption efficiency and the utilisation or retention of the vitamin in the body. The bioavailability of vitamins in nutritionally enriched foods should ideally be adjusted to achieve the dietary reference intake in a reasonable portion. Current vitamin biofortification programmes focus on the fat-soluble vitamins A and E, and the water-soluble vitamins C and B9 (folate), but the control of dosage and bioavailability has been largely overlooked. In the present review, we discuss the vitamin content of nutritionally enhanced foods developed by conventional breeding and genetic engineering, focusing on dosage and bioavailability. Although the biofortification of staple crops could potentially address micronutrient deficiency on a global scale, further research is required to develop effective strategies that match the bioavailability of vitamins to the requirements of the human diet.
    Nutrition Research Reviews 10/2013; · 3.86 Impact Factor
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    ABSTRACT: Antibodies are an important class of proteins that can be used for the prevention, treatment and diagnosis of many diseases. Consequently, there is an intense and growing demand for recombinant antibodies, placing immense pressure on current production capacity which is based largely on microbial cultures and mammalian cells. Alternative systems for cost effective antibody production would be very welcome, and plants are now gaining widespread acceptance as green bioreactors with advantages in terms of cost, scalability and safety. Several plant-produced antibodies (plantibodies) are undergoing clinical trials and the first commercial approval could be only a few years away. The performance of the first generation of products has been very encouraging so far. In terms of product authenticity, differences in glycosylation between plantibodies and their mammalian counterparts have been defined, and the scientific evaluation of any possible consequences is underway. Ongoing studies are addressing the remaining biochemical constraints, and aim to further improve product yields, homogeneity and authenticity, particularly where the antibody is intended for injection into human patients. A remaining practical challenge is the implementation of large-scale production and processing under good manufacturing practice conditions that are yet to be endorsed by regulatory bodies. The current regulatory uncertainty and the associated costs represent an entry barrier for the pharmaceutical industry. However, the favourable properties of plants are likely to make the plant systems a useful alternative for small, medium and large scale production throughout the development of new antibody-based pharmaceuticals.
    Current Pharmaceutical Design 10/2013; 11(19):2439 - 2457. · 3.29 Impact Factor
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    ABSTRACT: Molecular Pharming, the production of recombinant pharmaceuticals through plant biotechnology, has the potential to transform the biologics sector of the pharmaceutical industry. More fascinating however, is how it might be used to improve access to modern medicines, and improve health of the poor in developing countries and emerging economies. Although improving global health through molecular pharming has been discussed for at least two decades, little progress has actually been made. In this manuscript, a four point plan is described to maximise the opportunity for molecular pharming to provide solutions. These are (i) to identify and prioritise important drug targets that are relevant to the poor; (ii) to support research and development partners in low to middle income countries to develop local expertise, transfer technology and build capacity; (iii) to increase collaboration between regulatory bodies to enable national regulatory frameworks to be developed in low to middle income countries; and (iv) to promote intellectual property management approaches that include socially responsible licensing. An existing case study is described to illustrate how this might be achieved.
    Plant Biotechnology Journal 10/2013; · 6.28 Impact Factor
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    ABSTRACT: Cereal seeds are versatile platforms for the production of recombinant proteins because they provide a stable environment for protein accumulation. However, endogenous seed storage proteins include several prolamin-type polypeptides that aggregate and crosslink via intermolecular disulfide bridges, and these could potentially interact with multimeric recombinant proteins such as antibodies that assemble in the same manner. We investigated this possibility by sequentially extracting a human antibody expressed in maize endosperm, and by precipitation in vitro with zein. We provide evidence that a significant proportion of the antibody pool interacts with zein and therefore cannot be extracted using non-reducing buffers. Immunolocalization experiments demonstrated that antibodies targeted for secretion were instead retained within zein bodies because of such covalent interactions. Our findings suggest that the production of soluble recombinant antibodies in maize could be enhanced by eliminating or minimizing interactions with endogenous storage proteins.
    Biotechnology Journal 08/2013; · 3.71 Impact Factor
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    ABSTRACT: Plants adapt to abiotic stress by undergoing diverse biochemical and physiological changes that involve hormone-dependent signaling pathways. The effects of plant hormones can be mimicked by exogenous chemical regulators such as herbicide safeners, which not only enhance stress tolerance but also confer hormetic benefits such as increased vigor and yield. In this study, rice plants growing in normal and saline soils were exposed to abscisic acid (ABA), the safener cyprosulfamide or both compounds together. We found that cyprosulfamide, either alone or in combination with ABA, protected the plants from salinity stress and induced vigorous growth, including the formation of new tillers and early flowering. Proteomic analysis identified several proteins that were induced by stress and/or the chemical treatments, including the late embryogenesis abundant protein OsLEA3, a putative mitochondrial translocase and a putative fumarylacetoacetate hydrolase. The corresponding genes were induced by stress and/or the individual chemical treatments, but expression dropped back when the stress was removed. However, the combination of ABA and cyprosulfamide prolonged the expression of all three genes beyond the stress period, and allowed the plants to maintain their enhanced growth characteristics. These data support a model involving cooperation between the cyprosulfamide and ABA signaling pathways. Accordingly, it was found that cyprosulfamide induces ABA synthesis more robustly than salinity stress, allowing the two regulators to converge on certain downstream target genes. We discuss the impact of our results on current models for the hormonal regulation of stress response pathways in rice and other plants.
    Molecular Breeding 08/2013; · 2.28 Impact Factor
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    ABSTRACT: L-ascorbic acid (vitamin C) is an antioxidant and electron donor whose metabolism in plants is under strict feedback control. The factors that influence L-ascorbic acid accumulation in staple crops are only partially understood. One way to gain insight into the regulation of L-ascorbic acid metabolism is to investigate the endogenous pathways in various genetic backgrounds, and characterize their interactions with transgenes encoding relevant enzymes. In an initial step, we investigated the developmental profile of L-ascorbic acid accumulation in the endosperm of three diverse maize genotypes and a transgenic line expressing rice dehydroascorbate reductase, which enhances L-ascorbic acid recycling. We determined the transcript levels of all the key genes in the L-ascorbic acid metabolic pathways as well as the specific levels of ascorbic acid and dehydroascorbate. L-ascorbic acid levels were high 20 days after pollination and declined thereafter. We found significant genotype-dependent variations in the transcript levels of some genes, with particular complexity in the ascorbic acid recycling pathway. Our data will help to elucidate the complex mechanisms underlying the regulation of L-ascorbic acid metabolism in plants, particularly the impact of genetic background on the strict regulation of ascorbic acid metabolism in endosperm cells.
    Biotechnology Journal 06/2013; · 3.71 Impact Factor
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    ABSTRACT: A fast method was developed to determine carotenoid content in transgenic maize seeds. The analysis was carried out using an ultra-high performance liquid chromatograph coupled to a photodiode array detector and a mass spectrometer (UHPLC-PDA-MS/MS). Sixteen carotenoid pigments were detected and quantified in less than 13 min. In addition, it was possible to obtain good resolution of both polar xanthophylls and nonpolar carotenes. The method exhibited: (a) high degree of repeatability (%RSD below 13%); (b) linear calibration curves (R2>0.9952); (c) satisfactory recoveries for most of the pigments (between 82% and 108%); and (d) low detection (from 0.02 to 0.07 μg/mL) and quantification limits (0.05 to 0.20 μg/mL) (LOD and LOQ respectively). The methodology was applied to the analysis of transgenic maize lines TM1, TM2, and TM3, expressing several carotenogenic genes.
    Journal of Agricultural and Food Chemistry 05/2013; · 3.11 Impact Factor
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    ABSTRACT: The cDNAs from Hyoscyamus niger, encoding two enzymes of tropane-alkaloid biosynthesis, tropinone reductase I (TR-I) and hyoscyamine-6β-hydroxylase (H6H), have been simultaneously introduced into Nicotiana tabacum using particle bombardment and expressed under the control of the CaMV 35S promoter. Southern and Northern analyses confirmed integration and transcript accumulation for both tr1 and h6h. Fertile tobacco plants expressing both transgenes were regenerated and detached leaves of these plants were fed with tropinone and hyoscyamine, the substrates, respectively, of TR-I and H6H. Besides the expected TR-I and H6H reaction products, acetylated forms of tropine were also generated in these experiments, indicating that the expression of alkaloid-pathway enzymes in a transgenic background can produce unexpected substances. In addition, leaves of the transgenic plants showed in most cases higher nicotine content than leaves of control plants. Nicotine levels were approximately 3- to 13-fold higher in both the parental transgenic lines and in T1 progeny expressing functional TR-I and H6H, compared to levels in wild-type plants and in transgenic plants carrying the nptII transgene alone. In addition, nicotine related compounds such as anatabine, nornicotine, bipyridine, anabasine, and myosmine were identified in transgenic tobacco lines and below detection limit in wild-type plants, suggesting changes in the activity of the enzymes in the nicotine biosynthetic pathway in the transgenic background.
    Plant Science. 04/2013; 162:905-913.
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    ABSTRACT: A recent paper published in the journal Food and Chemical Toxicology presents the results of a long-term toxicity study related to a widely-used commercial herbicide (Roundup™) and a Roundup-tolerant genetically modified variety of maize, concluding that both the herbicide and the maize varieties are toxic. Here we discuss the many errors and inaccuracies in the published article resulting in highly misleading conclusions, whose publication in the scientific literature and in the wider media has caused damage to the credibility of science and researchers in the field. We and many others have criticized the study, and in particular the manner in which the experiments were planned, implemented, analyzed, interpreted and communicated. The study appeared to sweep aside all known benchmarks of scientific good practice and, more importantly, to ignore the minimal standards of scientific and ethical conduct in particular concerning the humane treatment of experimental animals.
    Transgenic Research 04/2013; 22(2). · 2.28 Impact Factor
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    ABSTRACT: Carotenoids are a diverse group of tetraterpenoid pigments found in plants, fungi, bacteria and some animals. They play vital roles in plants and provide important health benefits to mammals including humans. We previously reported the creation of a diverse population of transgenic maize plants expressing different carotenogenic gene combinations and exhibiting distinct metabolic phenotypes. Here we carried out an in depth targeted mRNA and metabolomic analysis of the pathway to characterize the specific impact of five carotenogenic transgenes and their interactions with twelve endogenous genes in four different transgenic lines representing distinct genotypes and phenotypes. We reconstructed the temporal profile of the carotenoid pathway during endosperm development at the mRNA and metabolic levels (for total and individual carotenoids) and investigated the impact of transgene expression on the endogenous pathway. These studies enabled us to investigate the extent of any interactions between the introduced transgenic and native partial carotenoid pathways during maize endosperm development. Importantly, we developed a theoretical model which explains these interactions, and suggest functioning modes for the pathway that identify intervention points allowing the maize endosperm carotenoid pathway to be engineered in a more effective and predictable manner. This article is protected by copyright. All rights reserved.
    The Plant Journal 04/2013; · 6.82 Impact Factor

Publication Stats

9k Citations
1,180.09 Total Impact Points


  • 2008–2014
    • Catalan Institution for Research and Advanced Studies
      Barcino, Catalonia, Spain
    • Newcastle University
      • School of Biology
      Newcastle upon Tyne, ENG, United Kingdom
  • 2005–2014
    • Universitat de Lleida
      • Department of Vegetal Production and Forestry Science
      Lérida, Catalonia, Spain
  • 2013
    • Changchun Normal University
      Hsin-ching, Jilin Sheng, China
    • IRB Lleida Biomedical Research Institute of Lleida
      Lérida, Catalonia, Spain
  • 1995–2013
    • John Innes Centre
      • Department of Cell and Developmental Biology
      Norwich, England, United Kingdom
  • 2010–2012
    • Northeast Normal University
      • School of Life Sciences
      Changchun, Jilin Sheng, China
  • 2004–2006
    • RWTH Aachen University
      • Institute of Biology VII (Molecular Biotechnology)
      Aachen, North Rhine-Westphalia, Germany
    • Institute of Molecular Biology
      Mayence, Rheinland-Pfalz, Germany
    • University of Minnesota Duluth
      Duluth, Minnesota, United States
    • The University of York
      • Department of Biology
      York, England, United Kingdom
  • 2003–2006
    • Fraunhofer Institute for Molecular Biology and Applied Ecology IME
      • Department of Plant Biotechnology
      Aachen, North Rhine-Westphalia, Germany
  • 1998–2000
    • Durham University
      • School of Biological and Biomedical Sciences
      Durham, England, United Kingdom
    • Purdue University
      • Department of Botany and Plant Pathology
      West Lafayette, IN, United States