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Biomedical subjects

Anne Osbourn

Publications and source records attributed to Anne Osbourn.

7 recordsLinked to original sources
PubMed2006

A different function for a member of an ancient and highly conserved cytochrome P450 family: from essential sterols to plant defense.

CYP51 sterol demethylases are the only cytochrome P450 enzymes with a conserved function across the animal, fungal, and plant kingdoms (in the synthesis of essential sterols). These highly conserved enzymes, which are important targets for cholesterol-lowering drugs, antifungal agents, and herbicides, are regarded as the most ancient member cytochrome P450 family. Here we present a report of a CYP51 enzyme that has acquired a different function. We show that the plant enzyme AsCYP51H10 is dispensable for synthesis of essential sterols and has been recruited for the production of antimicrobial compounds (avenacins) that confer disease resistance in oats. The AsCyp51H10 gene is synonymous with Sad2, a gene that we previously had defined by mutation as being required for avenacin synthesis. In earlier work, we showed that Sad1, the gene encoding the first committed enzyme in the avenacin pathway (beta-amyrin synthase), had arisen by duplication and divergence of a cycloartenol synthase-like gene. Together these data indicate an intimate evolutionary connection between the sterol and avenacin pathways. Sad1 and Sad2 lie within 70 kb of each other and are expressed specifically in the epidermal cells of the root tip, the site of accumulation of avenacins. These findings raise intriguing questions about the recruitment, coevolution, and regulation of the components of this specialized defense-related metabolic pathway.

Amino Acid Sequence↗
PubMed2006

The poetry of science.

During the past year, I have taken part in an experiment in which I have been the experimental animal. I was awarded a fellowship that gave me the opportunity to take a sabbatical from science and spend a year in the School of Literature and Creative Writing at the University of East Anglia. The School of Literature and Creative Writing is internationally renowned, and past students include household names such as Ian McEwan, Kazuo Ishiguro, Trezza Azzopardi and Tracy Chevalier. I have a keen interest in creative writing and had written a few short stories. This was a formidable but thrilling challenge. During my adventure, I realized that, in many ways, I was coming home.

Communication↗
PubMed2006

First encounters--deployment of defence-related natural products by plants.

Plant-derived natural products have important functions in ecological interactions. In some cases these compounds are deployed to sites of pathogen challenge by vesicle-mediated trafficking. Polar vesicle trafficking of natural products, proteins and other, as yet uncharacterized, cargo is emerging as a common theme in investigations of diverse disease resistance mechanisms in plants. Root-derived natural products can have marked effects on interactions between plants and soilborne organisms, for example by serving as signals for initiation of symbioses with rhizobia and mycorrhizal fungi. They may also contribute to competitiveness of invasive plant species by inhibiting the growth of neighbouring plants (allelopathy). Very little is known about the mechanisms of release of natural products from aerial plant parts or from roots, although there are likely to be commonalities in these processes. There is increasing evidence to indicate that pathogens and symbionts can manipulate plant endomembrane systems to suppress host defence responses and facilitate accommodation within plant cells. The relationship between secretory processes and plant interactions forms the focus of this review, which brings together different aspects of the deployment of defence-related natural products by plants.

ATP-Binding Cassette Transporters↗
PubMed2006

Dual effects of plant steroidal alkaloids on Saccharomyces cerevisiae.

Many plant species accumulate sterols and triterpenes as antimicrobial glycosides. These secondary metabolites (saponins) provide built-in chemical protection against pest and pathogen attack and can also influence induced defense responses. In addition, they have a variety of important pharmacological properties, including anticancer activity. The biological mechanisms underpinning the varied and diverse effects of saponins on microbes, plants, and animals are only poorly understood despite the ecological and pharmaceutical importance of this major class of plant secondary metabolites. Here we have exploited budding yeast (Saccharomyces cerevisiae) to investigate the effects of saponins on eukaryotic cells. The tomato steroidal glycoalkaloid alpha-tomatine has antifungal activity towards yeast, and this activity is associated with membrane permeabilization. Removal of a single sugar from the tetrasaccharide chain of alpha-tomatine results in a substantial reduction in antimicrobial activity. Surprisingly, the complete loss of sugars leads to enhanced antifungal activity. Experiments with alpha-tomatine and its aglycone tomatidine indicate that the mode of action of tomatidine towards yeast is distinct from that of alpha-tomatine and does not involve membrane permeabilization. Investigation of the effects of tomatidine on yeast by gene expression and sterol analysis indicate that tomatidine inhibits ergosterol biosynthesis. Tomatidine-treated cells accumulate zymosterol rather than ergosterol, which is consistent with inhibition of the sterol C(24) methyltransferase Erg6p. However, erg6 and erg3 mutants (but not erg2 mutants) have enhanced resistance to tomatidine, suggesting a complex interaction of erg mutations, sterol content, and tomatidine resistance.

Alkaloids↗
PubMed2005

Comparative transcriptomics of rice reveals an ancient pattern of response to microbial colonization.

Glomalean fungi induce and colonize symbiotic tissue called arbuscular mycorrhiza on the roots of most land plants. Other fungi also colonize plants but cause disease not symbiosis. Whole-transcriptome analysis using a custom-designed Affymetrix Gene-Chip and confirmation with real-time RT-PCR revealed 224 genes affected during arbuscular mycorrhizal symbiosis. We compared these transcription profiles with those from rice roots that were colonized by pathogens (Magnaporthe grisea and Fusarium moniliforme). Over 40% of genes showed differential regulation caused by both the symbiotic and at least one of the pathogenic interactions. A set of genes was similarly expressed in all three associations, revealing a conserved response to fungal colonization. The responses that were shared between pathogen and symbiont infection may play a role in compatibility. Likewise, the responses that are different may cause disease. Some of the genes that respond to mycorrhizal colonization may be involved in the uptake of phosphate. Indeed, phosphate addition mimicked the effect of mycorrhiza on 8% of the tested genes. We found that 34% of the mycorrhiza-associated rice genes were also associated with mycorrhiza in dicots, revealing a conserved pattern of response between the two angiosperm classes.

DNA, Complementary↗