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SESSION 1 - Discovery - New horizons in plant pathology - page 36 / 65





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Molecular characterisation of the mycoparasite Pythium oligandrum by EST and proteome analysis

Neil R. Horner and Pieter van West

Aberdeen Oomycete Group, College of Life Sciences and Medicine, University of Aberdeen, Foresterhill, Aberdeen, AB24 2ZD, UK. Email: p.vanwest@abdn.ac.uk

Employing biological control strategies to suppress root-infecting oomycetes using bacterial, fungal or oomycete antagonists, is an area of increasing research interest. This work is driven in part by concerns over the use of chemicals in the environment and the drive to look for alternative disease control strategies. Oomycete mycoparasites such as Pythium oligandrum are capable of suppressing various soil-borne oomycete plant pathogens. Growth of P. oligandrum hyphae towards Phytophthora cells induces changes in the host cells, including retraction of the plasma membrane and cytoplasmic disorganisation. Interestingly, P. oligandrum is able to penetrate these thickened host cell walls, suggesting it secretes cellulolytic enzymes. We hypothesise that P. oligandrum produces a range of extra-cellular enzymes, including cellulases, proteases, lipases, and others, that facilitate mycoparasitism of oomycete plant pathogens. Our aims are to sequence 1000 EST’s of a P. oligandrum and P. infestans interaction cDNA libraries and perform proteomic analysis of secreted protein preparations from P. oligandrum. Interesting candidate genes that may be involved in mycoparasitism will be silenced using RNAi and functional characterization of these mutants will be performed. Here we present and discuss our latest results.


A proteomic approach to identify extracellular and cell wall proteins involved in the Phytophthora infestans – plant interaction

Catherine R. Bruce, Laura J. Grenville-Briggs, Alison Williams and Pieter van West

Aberdeen Oomycete Group, College of Life Sciences and Medicine, University of Aberdeen, Foresterhill, Aberdeen, AB24 2ZD, UK. Email: p.vanwest@abdn.ac.uk

A thorough understanding of the molecular events taking place during interactions between Phytophthora infestans and host and non-host plants is crucial for developing new control strategies. At the plant-pathogen interface, an exchange of molecular signals is thought to determine the outcome of the interaction. We anticipate that secreted and cell wall proteins will be rich in important signalling molecules involved in disease resistance or establishing successful infection. A proteomic approach is employed to identify novel extracellular and cell wall proteins from mycelia cultured in vitro and from plant intercellular fluid during P. infestanstomato interaction. At present we have identified over 40 protein spots. Several of these may represent effector molecules and these are characterised further. Here we present our latest results.


The cloning of ATR1Nd, an avirulence gene from Arabidopsis downy mildew

Anne P. Rehmany, Rebecca L. Allen and Jim L. Beynon

Warwick HRI, Wellesbourne, Warwick. CV35 9EF

In Peronospora parasitica (At) (downy mildew), the genetic determinants of cultivar-specific recognition by Arabidopsis thaliana are the ATR (A. thaliana-recognised) avirulence genes. We have used a map-based cloning strategy to target ATR1Nd, an avirulence gene recognised by the RPP1 (recognition of P. parasitica) resistance gene locus in Arabidopsis accession Niederzenz (Nd-1). Co-bombardment assays using plasmids expressing alleles of a candidate ATR1Nd gene together with GUS (each expressed from the 35S promoter) have demonstrated the specific recognition of ATR1Nd in plants carrying RPP1Nd. The RPP1 locus from Arabidopsis accession Wassilewskija (Ws-0) comprises three resistance genes with proven function (Botella et al., 1998; Plant Cell 10: 1847) which recognise a different set of Peronospora isolates from the Nd-1 RPP1 locus. Using co-bombardment assays, w e have tested whether our cloned ATR1Nd alleles are recognised by the RPP1Ws locus i. e. whether ATR1Nd and ATR1Ws are the same


Comparative study of zoospore encystment and pathogenicity of Phytophthora and Pythium species on plant roots

Yannis Raftoyannis1 and Michael W. Dick2

Department of Forestry, TEI Lamias, Karpenisi, 36100, Greece (rafto@teilam.gr), Department of Botany, University of Reading, Whiteknights, Reading RG6 2AS, UK

Eight plant species and twelve Pythium and Phytophthora species were used in a comparative study designed to investigate the effects of plant and fungal inter-specific variation on zoospore encystment density and distribution along root surfaces and pathogenicity. Zoospores showed differential encystment behaviour and they encysted more on dicotyledonous than on monocotyledonous plants. The monocotyledonous plants showed a non significant correlation between zoospore encystment and disease severity while the dicotyledonous plants showed a significant correlation. The fungal species could be separated into three groups according to their encystment-disease severity association: P. aphanidermatum, Ph. cactorum, P. coloratum, P. deliense, P. diclinum and Ph. nicotianae where a positive association between zoospore encystment density and disease severity was found; P. adhaerens, P. aquatile, P. dissimile and P. papillatum where a partial association was found; P. middletonii and P. torulosum where no association existed between zoospore encystment and disease severity.

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