Anne E Osbourn

Publications of Anne E Osbourn

• Formation of plant metabolic gene clusters within dynamic chromosomal regions.

  Authors: Ben Field, Anna-Sophie Fiston-Lavier, Ariane Kemen, Katrin Geisler, Hadi Quesneville, Anne E Osbourn

  Proceedings of the National Academy of Sciences of the United States of America. 08/2011; 108(38):16116-21.

  In bacteria, genes with related functions often are grouped together in operons and are cotranscribed as a single polycistronic mRNA. In eukaryotes, functionally related genes generally are scatteredIn bacteria, genes with related functions often are grouped together in operons and are cotranscribed as a single polycistronic mRNA. In eukaryotes, functionally related genes generally are scattered across the genome. Notable exceptions include gene clusters for catabolic pathways in yeast, synthesis of secondary metabolites in filamentous fungi, and the major histocompatibility complex in animals. Until quite recently it was thought that gene clusters in plants were restricted to tandem duplicates (for example, arrays of leucine-rich repeat disease-resistance genes). However, operon-like clusters of coregulated nonhomologous genes are an emerging theme in plant biology, where they may be involved in the synthesis of certain defense compounds. These clusters are unlikely to have arisen by horizontal gene transfer, and the mechanisms behind their formation are poorly understood. Previously in thale cress (Arabidopsis thaliana) we identified an operon-like gene cluster that is required for the synthesis and modification of the triterpene thalianol. Here we characterize a second operon-like triterpene cluster (the marneral cluster) from A. thaliana, compare the features of these two clusters, and investigate the evolutionary events that have led to cluster formation. We conclude that common mechanisms are likely to underlie the assembly and control of operon-like gene clusters in plants.

• High throughput screening of mutants of oat that are defective in triterpene synthesis.

  Authors: Bo Qin, John Eagles, Fred A Mellon, Panagiota Mylona, Luis Peña-Rodriguez, Anne E Osbourn

  Phytochemistry. 08/2010; 71(11-12):1245-52.

  The triterpenes are a large and diverse group of plant natural products that have important functions in plant protection and food quality, and a range of pharmaceutical and other applications. LikeThe triterpenes are a large and diverse group of plant natural products that have important functions in plant protection and food quality, and a range of pharmaceutical and other applications. Like sterols, they are synthesised from mevalonate via the isoprenoid pathway, the two pathways diverging after 2,3-oxidosqualene. During triterpene synthesis 2,3-oxidosqualene is cyclised to one of a number of potential products, the most common of these being the pentacyclic triterpene beta-amyrin. Plants often produce complex mixtures of conjugated triterpene glycosides which may be derived from a single triterpene skeleton. The delineation, functional analysis and exploitation of triterpene pathways in plants therefore represent a substantial challenge. Here we have carried out high throughput screening to identify mutants of diploid oat (Avena strigosa) that are blocked in the early steps of triterpene synthesis. We also show that mutants that are affected in the first committed step in synthesis of beta-amyrin-derived triterpenes, and so are unable to cyclise 2,3-oxidosqualene to beta-amyrin (sad1 mutants), accumulate elevated levels of primary sterols. The major differences were in Delta-7-campesterol and Delta-7-avenasterol, which both increased several fold relative to wild-type levels. This is presumably due to accumulation of squalene and 2,3-oxidosqualene and consequent feedback into the sterol pathway, and is consistent with previous reports in which specific oxidosqualene cyclase inhibitors and elicitors of triterpene biosynthesis were shown to have inverse effects on the flux through the sterol and triterpene pathways.

• Metabolic diversification--independent assembly of operon-like gene clusters in different plants.

  Authors: Ben Field, Anne E Osbourn

  Science (New York, N.Y.). 05/2008; 320(5875):543-7.

  Operons are clusters of unrelated genes with related functions that are a feature of prokaryotic genomes. Here, we report on an operon-like gene cluster in the plant Arabidopsis thaliana that isOperons are clusters of unrelated genes with related functions that are a feature of prokaryotic genomes. Here, we report on an operon-like gene cluster in the plant Arabidopsis thaliana that is required for triterpene synthesis (the thalianol pathway). The clustered genes are coexpressed, as in bacterial operons. However, despite the resemblance to a bacterial operon, this gene cluster has been assembled from plant genes by gene duplication, neofunctionalization, and genome reorganization, rather than by horizontal gene transfer from bacteria. Furthermore, recent assembly of operon-like gene clusters for triterpene synthesis has occurred independently in divergent plant lineages (Arabidopsis and oat). Thus, selection pressure may act during the formation of certain plant metabolic pathways to drive gene clustering.

• Capillary-induced contact guidance.

  Authors: Steven Lenhert, Ane Sesma, Michael Hirtz, Lifeng Chi, Harald Fuchs, Hans-Peter Wiesmann, Anne E Osbourn, Bruno M Moerschbacher

  Langmuir : the ACS journal of surfaces and colloids. 10/2007; 23(20):10216-23.

  Topographical features are known to impose capillary forces on liquid droplets, and this phenomenon is exploited in applications such as printing, coatings, textiles and microfluidics. SurfaceTopographical features are known to impose capillary forces on liquid droplets, and this phenomenon is exploited in applications such as printing, coatings, textiles and microfluidics. Surface topographies also influence the behavior of biological cells (i.e., contact guidance), with implications ranging from medicine to agriculture. An accurate physical description of how cells detect and respond to surface topographies is necessary in order to move beyond a purely heuristic approach to optimizing the topographies of biomaterial interfaces. Here, we have used a combination of Langmuir-Blodgett lithography and nanoimprinting to generate a range of synthetic microstructured surfaces with grooves of subcellular dimensions in order to investigate the influence of capillary forces on the biological process of contact guidance. The physical-chemical properties of these surfaces were assessed by measuring the anisotropic spreading of sessile water droplets. Having established the physical properties of each surface, we then investigated the influence of capillary forces on the processes of cellular contact guidance in biological organisms, using mammalian osteoblasts and germinating fungal spores as tester organisms. Our results demonstrate that capillary effects are present in topographical contact guidance and should therefore be considered in any physical model that seeks to predict how cells will respond to a particular surface topography.

• The rice leaf blast pathogen undergoes developmental processes typical of root-infecting fungi.

  Authors: Ane Sesma, Anne E Osbourn

  Nature. 10/2004; 431(7008):582-6.

  Pathogens have evolved different strategies to overcome the various barriers that they encounter during infection of their hosts. The rice blast fungus Magnaporthe grisea causes one of the mostPathogens have evolved different strategies to overcome the various barriers that they encounter during infection of their hosts. The rice blast fungus Magnaporthe grisea causes one of the most damaging diseases of cultivated rice and has emerged as a paradigm system for investigation of foliar pathogenicity. This fungus undergoes a series of well-defined developmental steps during leaf infection, including the formation of elaborate penetration structures (appressoria). This process has been studied in great detail, and over thirty M. grisea genes that condition leaf infection have been identified. Here we show a new facet of the M. grisea life cycle: this fungus can undergo a different (and previously uncharacterized) set of programmed developmental events that are typical of root-infecting pathogens. We also show that root colonization can lead to systemic invasion and the development of classical disease symptoms on the aerial parts of the plant. Gene-for-gene type specific disease resistance that is effective against rice blast in leaves also operates in roots. These findings have significant implications for fungal development, epidemiology, plant breeding and disease control.

• Purification, crystallization and preliminary X-ray diffraction analysis of a fungal saponin-detoxifying enzyme.

  Authors: Vicki A Bamford, Ola O Kolade, Anne E. Osbourn, Andrew M Hemmings

  Acta crystallographica. Section D, Biological crystallography. 08/2004; 60(Pt 7):1331-3.

  Tomatinase, an extracellular enzyme belonging to family 3 of the glycosyl hydrolases, is produced by the fungal tomato-leaf pathogen Septoria lycopersici and detoxifies the saponin alpha-tomatine. AnTomatinase, an extracellular enzyme belonging to family 3 of the glycosyl hydrolases, is produced by the fungal tomato-leaf pathogen Septoria lycopersici and detoxifies the saponin alpha-tomatine. An efficient strategy for purification of the enzyme from fungal culture medium has been developed. Single crystals have been grown by vapour diffusion at 289 K from 17.5%(w/v) PEG 4K, 5%(v/v) 2-propanol and 0.1 M sodium acetate pH 4.5 as precipitant. When cryoprotected at 100 K, these crystals diffract to at least 3.0 A and belong to space group P2(1)2(1)2. Based on an estimated molecular weight of 110 kDa for the glycosylated protein and assuming two molecules in the asymmetric unit, the crystals contain approximately 46% solvent.

• 2003 Asilomar meeting report.

  Authors: N Ronald Morris, Anne E Osbourn

  Fungal genetics and biology : FG & B. 03/2004; 41(2):109-14.

• Molecular cloning and characterization of triterpene synthases from Medicago truncatula and Lotus japonicus.

  Authors: Iñaki Iturbe-Ormaetxe, Kosmas Haralampidis, Kalliopi Papadopoulou, Anne E Osbourn

  Plant molecular biology. 04/2003; 51(5):731-43.

  Cloning of OSCs required for triterpene synthesis from legume species that are amenable to molecular genetics will provide tools to address the importance of triterpenes and their derivatives duringCloning of OSCs required for triterpene synthesis from legume species that are amenable to molecular genetics will provide tools to address the importance of triterpenes and their derivatives during normal plant growth and development and also in interactions with symbionts and pathogens. Here we report the cloning and characterization of a total of three triterpene synthases from the legume species Medicago truncatula and Lotus japonicus. These include a beta-amyrin synthase from M. truncatula (MtAMY1) and a mixed function triterpene synthase from Lotus japonicus (LjAMY2). A partial cDNA predicted to encode a beta-amyrin synthase (LjAMY1) was also isolated from L. japonicus. The expression patterns of MtAMY1, LjAMY1 and LjAMY2 and of additional triterpene synthases previously characterised from M. truncatula and pea differ in different plant tissues and during nodulation, suggesting that these enzymes may have distinct roles in plant physiology and development.

• Saponins in cereals.

  Authors: Anne E Osbourn

  Phytochemistry. 02/2003; 62(1):1-4.

  Saponins are a diverse family of secondary metabolites that are produced by many plant species, particularly dicots. These molecules commonly have potent antifungal activity and their natural role inSaponins are a diverse family of secondary metabolites that are produced by many plant species, particularly dicots. These molecules commonly have potent antifungal activity and their natural role in plants is likely to be in protection against attack by pathogenic microbes. They also have a variety of commercial applications including use as drugs and medicines. The enzymes, genes and biochemical pathways involved in the synthesis of these complex molecules are largely uncharacterized for any plant species. Cereals and grasses appear to be generally deficient in saponins with the exception of oats, which produce both steroidal and triterpenoid saponins. The isolation of genes for saponin biosynthesis from oats is now providing tools for the analysis of the evolution and regulation of saponin biosynthesis in monocots. These genes may also have potential for the development of improved disease resistance in cultivated cereals.

• Biosynthesis of triterpenoid saponins in plants.

  Authors: Kosmas Haralampidis, Miranda Trojanowska, Anne E Osbourn

  Advances in biochemical engineering/biotechnology. 02/2002; 75:31-49.

  Many different plant species synthesise triterpenoid saponins as part of their normal programme of growth and development. Examples include plants that are exploited as sources of drugs, such asMany different plant species synthesise triterpenoid saponins as part of their normal programme of growth and development. Examples include plants that are exploited as sources of drugs, such as liquorice and ginseng, and also crop plants such as legumes and oats. Interest in these molecules stems from their medicinal properties, antimicrobial activity, and their likely role as determinants of plant disease resistance. Triterpenoid saponins are synthesised via the isoprenoid pathway by cyclization of 2,3-oxidosqualene to give primarily oleanane (beta-amyrin) or dammarane triterpenoid skeletons. The triterpenoid backbone then undergoes various modifications (oxidation, substitution and glycosylation), mediated by cytochrome P450-dependent monooxygenases, glycosyltransferases and other enzymes. In general very little is known about the enzymes and biochemical pathways involved in saponin biosynthesis. The genetic machinery required for the elaboration of this important family of plant secondary metabolites is as yet largely uncharacterised, despite the considerable commercial interest in this important group of natural products. This is likely to be due in part to the complexity of the molecules and the lack of pathway intermediates for biochemical studies. Considerable advances have recently been made, however, in the area of 2,3-oxidosqualene cyclisation, and a number of genes encoding the enzymes that give rise to the diverse array of plant triterpenoid skeletons have been cloned. Progress has also been made in the characterisation of saponin glucosyltransferases. This review outlines these developments, with particular emphasis on triterpenoid saponins.