BSPP News Spring 2000 - Online EditionThe Newsletter of the British Society for Plant Pathology
Number 36, Spring 2000
Conference and Travel Reports
This workshop attracted well over 60 participants from all countries of the world. It was superbly and hospitably organised by CIMMYT staff at the main CIMMYT site near Mexico City. Discussions lasted from Monday 20 to Friday 24 September 1999, but most participants arrived on Saturday or Sunday, and the workshop benefited greatly from the informal discussion this facilitated. Quite why airlines spend less on fuel if the passenger stays over a Saturday is a piece of physics I think I must have slept through as an undergraduate, but in this case at least it was a great help in acclimatising and in making friends. Written papers were prepared in advance and distributed to participants on arrival, but the small size and long duration of the conference avoided the stultifying effect this can have. I would emphasise the excellence of the local arrangements; but I would also stress that this excellence led to genuine good relationships and dialogue that will bear fruit a long time in the future. It is the only meeting I have ever been to where at the banquet everyone ended up dancing.
All aspects of Septoria research were covered but the applied focus of the workshop was probably on breeding for resistance and associated genetic questions such as the extent of pathogen adaptation to different cultivars. Interests in epidemiology and chemical control were less well represented, but I made useful international contacts in these areas (US, Germany, Tunisia for example – not to mention very useful discussions with other UK delegates) and learnt much from the breeders. I gave a talk and poster, the talk enlivened by the embarrassing and instant collapse of a rather attractive theory when I turned out to have misinterpreted some published data: at least the author was there to gracefully correct me! It is a tribute to the spirit of the meeting that I did not feel damned by my mistake.
On the flippant side I was excited to visit the Toluca valley, the ancestral
home of Phytophthora infestans, even though we looked only at wheat,
and to eat maize smut. If you have tourist time I would also
thoroughly recommend the pyramids at Teotihuacan! I am most
grateful to the BSPP for topping up other funding and enabling me to attend
M W Shaw
University of Reading
This symposium was held at the John Innes Centre (JIC) in Colney. 214 delegates attended, from 33 countries, and a wide range of scientific information was presented. As a first year post-graduate, the purpose of my visit was to gain a wider knowledge of the scientific research being carried out in my field, as well as to meet others working on related topics who may be able to pass on useful information. I also prepared a poster of my initial results in collaboration with Dr Sharon Hall (IACR Rothamsted) entitled "Elemental Sulphur Metabolism in Plants and Defence Against Fungal Pathogens".
The first evening we attended the 18th Bateson Memorial Lecture presented by Professor Eugene Nester on "The Agrobacterium Story". Emphasis was placed on looking at the transfer of these foreign components into the host, particularly the involvement of both Ti plasmid and chromosome encoded virulence genes. This system was then compared to that of other plant and animal pathogens also able to transfer proteins into their host cells.
Wednesday morning began with an introduction and welcome by Mike Gale, Director of JIC, and was followed by the first session of the day, entitled "Early Events". Ulla Bonas firstly discussed how the bacterial pathogen Xanthomonas campestris is able to conquer the host, focusing mainly on the connection between bacterial hrp genes and avirulence genes. Dierk Scheel followed with a presentation on the early plant receptor-mediated events in cultured parsley cells treated with an elicitor from the pathogen Phytophthora sojae. Tina Romeis then talked about early signalling events in the Avr9/Cf-9-dependent defence response of tomato to Cladosporium fulvum. In both P. sojae and Cf-9 incompatible systems, the earliest responses appeared to be the same; ion fluxes across the plasma membrane, transient increases in cytosolic calcium levels, activation of mitogen-activated type protein (MAP) kinases and production of reactive oxygen species. Joerg Kämper then presented information on the regulation of pathogenic development in the smut fungus of maize, Ustilago maydis. The final talk of this session, presented by Max Dow, looked at lipopolysaccharides (LPS) and plant responses to phytopathogenic bacteria.
After lunch session two, entitled "Reprogramming Metabolism" began with Julie Scholes describing how Albugo candida was able to alter the regulation of photosynthetic and carbon metabolism in discrete areas of infected Arabidopsis leaves. This presentation was followed by Uwe Sonnewald who was also looking at changes in photosynthesis and carbohydrates but in the interaction between tobacco and potato virus Y (PVY). Andy Maule continued the virus theme by talking about programmed responses to virus infection in plants. The advancing front of virus infection was used to relate cellular responses to virus replication in time and space in two susceptible plants, cucurbit and pea. The final talk of the day was by Anne Osbourn on pre-formed antimicrobial defences in plants. Emphasis was placed on the plant secondary metabolites, saponins. Plant mutants lacking saponins were shown to have compromised disease resistance possibly as a direct consequence of saponin deficiency. It was also found that Gaeumannomyces graminis required the ability to detoxify saponins in order to infect oat. This implied that saponins were very important in disease resistance. This wrapped up the day's presentations and the entertainment for this evening was the conference dinner. I did not attend due to limited funds but was informed that it was a very enjoyable evening by everyone that I spoke to.
Thursday's Session three was entitled "Cellular Responses". First on stage was Michael Lyngkjaer with a presentation entitled "Potentiation of cellular resistance against powdery mildew". Many studies on resistance against powdery mildew have used single inoculation procedures to infect plants, however in the field plants are subject to repeated attacks. Therefore the group were investigating novel resistance mechanisms expressed after a double inoculation procedure. This was followed by a second talk on defence against powdery mildew given by Paul Schulze-Lefert. Here emphasis was placed on the further understanding of resistance mechanisms already in use against this pathogen. The theme then moved to viruses. Vitaly Citovsky began with an insight into movement of plant viruses through cell walls by plasmodesmata. Movement is thought to be mediated by a specialised viral movement protein which was shown to be phosphorylated only by the host. A short section on monopartite geminiviruses then followed where it was demonstrated that the coat protein carried functional nuclear import and export signals implicating it in nuclear shuttling of the viral genomic DNA. The geminivirus theme was continued with a talk by Dave Bisaro on the role of the geminivirus protein (TrAP) in host defence suppression. In the final presentation before lunch Edward Farmer discussed "oxylipin signatures". These were defined as "the global pattern and dynamics of oxylipin" and were found to change dramatically during pathogenesis.
Greg Martin initiated Session four on "Resistance Pathways", with a presentation on pathogen recognition, signal transduction, and gene expression in Pto-mediated disease resistance of tomato to Pseudomonas syringae pv. tomato. In this interaction there is a direct interaction of AvrPto and Pto proteins and it was shown that specific residues in the kinase subdomain VIII were required for this interaction. The second talk, presented by Jane Parker, was on the RPP5-gene mediated signalling pathway between Arabidopsis and Peronospora parasitica. The emphasis then turned to virus resistance. David Baulcombe enlightened us on two types of plant defence where antiviral mechanisms were activated following detection of the pathogen. The first was a gene-for-gene interaction following recognition of the viral coat protein, resulting in either a one or two phase response. The primary phase commonly resulted in suppression of the virus but if unsuccessful and accumulation of the virus occurred a secondary phase was activated resulting in HR. The second defence mechanism discussed was RNA-mediated and initiated by double stranded RNA of the virus in the infected plant. Antisense RNA targeted to the viral genome was found to be produced by the plant to inhibit the virus.
The final talk of the day was given by Simon Covey entitled "The response of Crucifers to virus infection: Attack and Defence or modus vivendi?" He put forward the concept that not all plant-virus interactions resulted in plant death despite systemic infection and development of disease symptoms. Occasionally, as in the case of some Brassica species to CaMV, transient symptoms occur before recovery. It was suggested that there was a balance between viral activity and host defence mechanisms. The day ended with a poster session and BBQ at JIC. There was a very wide range of posters on display each focusing on a different aspect of attack or defence, encompassing many different pathogens and hosts. This was where I contributed to the symposium, by presenting my poster and answering any questions on my research. This evening proved to be invaluable as it provided me with an ideal opportunity to discuss my work in a relaxed atmosphere with other delegates who were all willing to give their thoughts and ideas.
John Pickett started the final session headed Remote Responses with a very interesting view that plants may resist attacking insects through the production of compounds which modify insect development and behaviour without a direct physiological effect. However these same signals could also be exploited by colonising organisms particularly pathogens and insect pests. This was followed by a talk by John Draper on SAR in tobacco, particularly the effect of salicylic acid (SA) suppression. This was followed by information on wound signalling during leaf injury presented by Diana Bowles. Chris Lamb then discussed an activation tagging approach to the dissection of disease resistance signal networks. The final presentation of the conference was the BSPP lecture given by Jeff Dangl on "mechanisms of specific disease resistance: current understanding and future challenges". We were reminded of how research involving heritable disease resistance has evolved from Flor's gene-for-gene hypothesis in the 1940's, to cloning of avirulence genes and isolation and characterisation of disease resistance genes. This evolution is still continuing with more molecular and cellular detail being added to our knowledge of how specific interactions initiate responses leading to disease resistance and induction of systemic responses. Jeff then talked about the work of his own lab involving the relationship between the Rpm 1 gene of Arabidopsis and avrRpm1 of P.syringae pv tomato along with the basic problems that they were struggling with.
All too soon the symposium was declared closed. We attended a final lunch provided by the Sainsbury Laboratory Council to celebrate the tenth anniversary of the opening of the Sainsbury Laboratory before commencing the journey home. The symposium had been tiring but a very worthwhile experience providing me with a wealth of new information, contacts and ideas from which I shall benefit greatly.
The symposium was supported by the John Innes Foundation, British Society
for Plant Pathology, Novartis Crop Protection AG, Unilever Research and
Zeneca Agrochemicals. I would like to thank BSPP for the funding which
enabled me to participate.
University of Bath