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Garrett Memorial Lecture

“I am a Pathologist”

Professor Hugh Pennington,

Dept of Medical Microbiology, University of Aberdeen, UK

There is a paradox. Thanks to science we are living longer than at any time in history. We are better fed than ever before. And we die mostly of diseases of old age rather than from pathogen attack. Plenty is the problem rather than famine. But the public is afraid. Scientists are seen as Frankenstein-like figures. Why is this so?

In my talk I will try to identify the reasons and will suggest ways forward. My illustrations will include pathogens: prions, E.coli O157, foot and mouth disease and smallpox.

SESSION 1  - Discovery - New horizons in plant pathology

The role of genes and their products in plant pathology

Jim Beynon

Warwick HRI, University of Warwick, Wellesbourne, Warwick, CV35 9EF.

The invasion of plants by biotrophic pathogens is an elegant and co-ordinated process. Lacking an adaptive immune system, the host relies on innate immunity processes and a second line of defence, consisting of receptor/response (resistance) gene proteins, that prevent pathogen growth and reproduction by eliciting a resistance reaction.  These resistance responses can be immediate or involve prolonged and extensive changes in gene expression and often result in local tissue death known as the hypersensitive response.  Faced with these barriers to invasion potential plant pathogens must suppress or avoid triggering the innate immune responses and the resistance gene dependent responses.  Therefore, plant pathogens have evolved a range of proteins (pathogenicity factors or effectors), targeted towards the plant cell, that are necessary for effective colonisation of host tissue.  Understanding the nature of these gene products and their role in planta will reveal key insights not only into the mechanisms of pathogenicity but also host defence.

Isolation of genes expressed during compatible interactions between leaf rust (Puccinia triticina) and wheat using cDNA-AFLP and haustorial isolation

Lin Zhang, Helen Meakin and Matt Dickinson

School of Biosciences, University of Nottingham, Loughborough LE12 5RD, UK

Puccinia triticina is an excellent model system for isolating genes expressed during compatible interactions between obligate biotrophic basidiomycete fungi and plants because of the synchronous infection that occurs when urediospores are inoculated onto a susceptible host. The fungus goes through a number of developmental stages to form intercellular hyphae and haustoria within the plant. We have developed and utilised two techniques to isolate fungal and plant genes expressed during this process. Using cDNA-AFLP, we have isolated fragments of wheat and rust genes that are expressed at specific defined time-points during the infection process. A number of these sequences have been used as probes in northern hybridisations and in real-time PCR to confirm their expression patterns, and have also been characterised by PCR analysis and Southern hybridisations to determine which are of fungal or wheat origin. A full-length cDNA library has been constructed from day 5 and 7 post-inoculation pooled cDNAs, and this library has been screened to isolate full-length cDNAs of selected fungal and wheat sequences. In the second approach, we have purified haustoria from infected plants, and used cDNA from these to isolate additional haustorial-specific sequences from the library. The results from the sequence analysis of these clones, which has revealed significant similarities amongst the fungal genes to a chitinase, an arabitinol dehydrogenase and a metallothionein, and in wheat to a katanin and a cell enlargement protein, will be discussed. Approximately 50% of the sequences obtained had no significant homology to sequences in databases.

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