BSPP News Summer 2001 - Online Edition

The Newsletter of the British Society for Plant Pathology
Number 39, Summer 2001 

Conference and Travel Reports

BSPP Presidential Meeting 2000 "Plant-pathogen interactions: Understanding mechanisms of resistance and pathogenicity for disease control". Imperial College at Wye, Kent, UK: 18 - 20 December 2000

The BSPP Presidential Meeting, held at Wye, was a successful, well-attended event. Withersdane Hall was a pleasant setting for the event, and the weather was seasonal, with grey, misty mornings (I have no idea how the rest of the days were outside!). Around 200 delegates were present to hear an array of talks on plant-microbe interactions. The speakers dealt with a range of microbial organisms, with the emphasis very clearly on early stages of plant-pathogen interactions. Both compatible and incompatible systems were examined, with several authors seeking to draw parallels between plant and animal responses. In addition, the continuing importance of Agrobacterium and particularly, Arabidopsis, was clear to all.

The Presidential keynote address delivered by Professor John Mansfield (Imperial College), set the stage for the subsequent invited presentations. He reviewed the various aspects of pathogen-host interactions studied using classical examples. His lecture covered his past and present experience in phytoalexins, their biosynthetic pathways and detoxification by fungi, localized plant defence mechanisms and their cellular coordination in a range of plants such as Arabidopsis, bean, lettuce, onion and pepper. He described cellular disorganisation in cells undergoing the hypersensitive reaction (HR), cell wall modification and accumulation of hydrogen peroxide at reaction sites challenged by bacteria. He also described suppression of resistance, hrp genes and type III secretion system and protein injection by plant pathogenic bacteria. His talk was really outstanding and provided an opportunity to hear the most current research and theories in plant-pathogen interactions.

The first session on the opening afternoon was entitled "The Structural Framework". Simon Santa Cruz considered the N-gene response leading to HR induced by TMV in Nicotiana edwardsonii. Using a combination of GFP and blockage of HR at temperatures at or above 30°C, virus responses could be synchronously tracked over time. An attempt was made to link cell death seen in plant cells with that in animals based on Bax. Results suggest that Bax may be indirectly involved in challenged plant cell death. Tim Carver then gave an account of some fascinating experiments on the early stages of Blumeria graminis infection. These described the emergence of primary germ tubes from conidia. One experiment involved allowing conidia to contact leaves, and then turning some after 20 minutes. Virtually 100% of unturned spores germinated such that germ tubes contacted the leaf, whereas those that were turned, missed the leaf on most occasions.

On Tuesday morning a most compelling talk was given by Dr Anne Osbourne, who described some aspects of pathogenicity and host range determinants in root-infecting fungi. She focused on recent developments in knowledge of some selected groups of phytoalexins (i.e. saponins) as well as on the evidence for and against an attributed role for antifungal compounds in plant defence.

Thursday's session concerned pathogenicity of bacteria, fungi and virus. Andy Maule gave a very stimulating talk on the compatible host gene expression induced by virus infection especially cucumber mosaic virus (CMV). He pointed out that virus infection induced immediate and subsequent changes in host gene expression and has an impact on virus replication and movement. John P. Carr continued the virus theme by talking about inducing resistance virus-specific pathways to plant viruses. Emphasis was placed on the role of salicylic acid on resistance to tobacco mosaic virus (TMV). The final talk of this session was by Christian Boucher on the sequence of the genome of the bacteria Ralstonia solanacearum.

Professor Michele Heath (University of Toronto) gave the Garrett Memorial Lecture, entitled "Millennial milestones: concepts, molecules and genes". She traced the history and development of plant-parasite interaction studies in three areas and time periods, and nominated phytoalexins as her millennial molecule. There were three candidates for concept of the millennium, the hypersensitive response, the gene-for-gene hypothesis and induced resistance. However, it was clear in her mind that the most confused concept is non-host resistance, despite the emphasis on research in this area.

Richard Michelmore from the USA talked on natural and artificial evolution of resistance gene clusters in tomato and lettuce. He enlightened us on molecular characterization of the Dm3 and Pto plant resistance genes for Bremia lactucae and Pseudomonas syringae pv. tomato. Talks in this session contained several impressive examples of molecular aspects of plant resistance genes. Those given by J. Beynon and M. Coleman were on function and molecular characterization of resistance genes RPP13 (resistance gene for Peronospora parasitica) and RPW8 (resistance gene for powdery mildew) to two obligate biotroph fungi in Arabidopsis thaliana.

It was then time for the PH Gregory competition, where speakers who had not previously presented to a learned society were given their chance to perform. Alex Appiah from Silwood Park opened proceedings by talking about black pod of cocoa, a disease which causes thousands of millions of pounds worth of damage. Cocoa germplasm clones were being selected for resistance to the disease. Alex Collins from HRI Wellesbourne, presented her work on crucifer isolates of Verticillium dahliae and their interspecific hybridisation with Verticillium albo-atrum. Graeme Down presented his recent work on Spongospora subterranea f. sp. nasturtii, which causes crook root of watercress. Diagnostic, PCR-based testing, and phylogenetic relationships were covered. Sarah Holcroft from Wellesbourne talked about the requirement for basic scientific knowledge of bacterial leaf spot of ivy, focussing on genetic diversity (or lack of it). Hannah Jones of Oxford talked about Oidium lycopersici, a fungal pathogen of 13 host families. The work focussed on early stages of host-pathogen interactions, with penetration being the result of a combination of turgor pressure and cutinase activity.

N-mediated defence responses to TMV was the subject of Jack Pearts presentation. Research at the Sainsbury Laboratory had used a technique known as VIGS (Virus induced gene silencing) to follow this response in tobacco. The premise being that if N-gene function is silenced, resistance will not operate by this mechanism. The approach had revealed crucial roles for EDS1, and a novel gene, NRG1, in this pathway. Jane Williams of Bath, discussed the role of elemental sulphur in the resistance response of plants to Verticillium dahliae. GC-MS was used to follow sulphur accumulation in various host-pathogen interactions. The PH Gregory prize was closely contested, and won by Jack Peart from the Sainsbury Laboratory.

Wednesday's session four, entitled "resistance mechanisms, cellular signaling", began with Murray Grant on the uses of avrRpm1/RPM1 interaction to elucidate the signaling hierarchies associated with hypersensitive cell death caused by Pseudomonas seringae. This was followed by a second talk on plant recognition of Xanthomonas campestris effector proteins given by Eric Marois. Here emphasis was placed on further understanding the mechanisms of resistance in pepper plant carrying the resistance gene Bs3 to bacteria expressing the avirulence protein AvrBs3. The final talk of this session was by Radhika Desikan on signaling mechanisms leading to programmed cell death during the hypersensitive response in Arabidopsis thaliana.
In the next session, "local and systemic resistance", David Baulcombe gave a provoking presentation where he investigated the signaling component involved in Rx and Ry responses by using a system based on virus induced gene silencing. This prompted discussion about the application of this system in different examples of virus resistance.

In the session on local and systemic resistance, the genetics of resistance pathways was dissected. John Turner told delegates about the function of COI1, the mutant of which (coi1) is insensitive to jasmonic acid (JA). COI1 appears to be a F-box protein containing LRRs, with a functional role linking JA to the ubiquitin pathway. John Draper focussed on the interaction between JA and salicylic acid (SA) in resistance. Using the Pseudomonas syringae/ tobacco system, levels of JA and SA were found to fluctuate in areas where lesions would form, and expression of PDF1.2, PR1 and thionin was seen. Studies implied that synergism of JA and SA, was dependent on their concentrations. Chris Lamb then considered the dir1 phenotype, where no SAR is seen in challenged plants. To establish where DIR1 acts, petiole exudate was collected and concentrated from inoculated leaves, and transferred to a new plant of different genotype. DIR1 was then expressed in petiole exudate of the new plant, rather than downstream. Chris' hypothesis was that DIR1 could be the mobile element in SAR, or may be the chaperone or transporter for the mobile signal.

The meeting concluded with an examination of targets for intervention and disease control. Dr Kim Hammond-Kosack (Monsanto UK Ltd) described an applied approach to the control of Fusarium ear blight on cereals and the other final few talks covered the development and signalling of powdery mildew and NIM1/NPR1 as targets for disease control. Robert Dietrich talked about the potential of SAR as a target for exploitation. The Nim1 gene operates downstream of SA and is shown to correlate with PR1 expression. The NIM1 protein has a nuclear localisation signal. Attempts to overexpress Nim1 in Arabidopsis has led to the conclusion that NIM1 operates at an optimal level to cause resistance, and that this resistance in dependent upon SA.

These presentations were a great source of  information about the "exciting" science of gene silencing and transformation experiments going on all over the place. Unfortunately, the desire to identify genes and characterise their function seems to be relegating to the background one of the fundamental roles of plant pathology: finding effective solutions to crop disease problems world-wide. This observation was demonstrated in some of the presentations, where after long and expensive work aimed at identifying and modifying genes responsible for certain factors in the host-pathogen interaction, in vivo tests carried out at the latter stages failed.  Emphasis should still be placed on finding "what will do the job before we spend our time investigating how it did the job".

The meeting was very intensive with many contributions in each session. There was a lot of  discussion both in formal sessions and, especially, outside. I have returned home in an enthused frame of mind with a lot of new information and useful contacts with other scientists involved in plant pathology research. I was impressed by the quality of research that is being carried out in several organizations and institutions especially in Europe. The great future of this research can only be enhanced by the participation and collaboration of developed institutions, scientists and funding.

Compiled from reports by:
Bouchaib Bencharki, University of Hassan 1st, Morocco
Robert Zarnowski, Agricultural niversity of Wroclaw, Poland
Soner Soylu, University of Mustafa Kemal, Turkey
Alexandra Collins, Lucy Nott & Laura Grenville, HRI, Wellesbourne
Graeme Down, HRI East Malling
Alex Appiah, Imperial College

The Presidential Meeting of the British Society for Plant Pathology represented a veritable tour de force of plant pathology. The three-day annual meeting left most of us with innumerable ideas and enough to dwell on for the Christmas and well into the New Year! A broad range of topics were covered including detailed insights into pathogenicity, resistance mechanisms, signalling, structural studies and disease control; in fungal, bacterial and viral systems.

The Garrett Memorial Lecture, 'Millennial milestones: concepts, molecules and genes', given by Michele Heath, provided a historial context to the conference. She underlined with clarity, the developments within the world of plant pathology in the last century, or indeed the last 20 years!

The schedule and pace of the meeting were, at times, somewhat frenetic; and the number of talks was perhaps a little overwhelming. However, the majority of the talks were interesting and well presented. Here we mention a few which were especially enjoyable.

Tim Carver treated us to novel ideas and impressive pictures from the early development of the barley powdery mildew, Blumeria graminis, with an equally provocative title (perhaps not even qualifying as a single entendre)! Perception of the host within minutes after contact of pathogen on plant was clearly demonstrated, and sound arguments were presented for the rejection of previous theories for delayed host detection by fungal pathogen. Much of the pioneering work presented here was done by Tim's graduate student, Alison Wright, who was presenting at another meeting. The first day ended with a treasure hunt to the poster room, where a glass of wine and a plethora of pathological posters awaited us.

Andy Maule gave a highly interesting seminar (even to the uninitiated!), on the 'Complex spatial changes in gene expression in response to virus invasion of compatible hosts', with the developmental stages during virus infection covered with great clarity. Pulses were running high for the P.H. Gregory competition, which had a huge number of applicants compared to previous years. Congratulations to Jack Peart for his winning presentation on the 'Identification of genes required for N-mediated resistance against TMV by virus-induced gene silencing'. His talk was interesting and confidently presented and showed great style in more ways than one, with that fashionable BSPP T-shirt! The prize ceremony was given after the evening meal, together with a picture presented to Roy Johnson for his services to the BSPP council and for his Senior Editorship of Plant Pathology.

The final morning of any conference is always a difficult one, but at the Presidential Meeting, we were given a number of excellent talks, including a presentation by Radhika Desikan on programmed cell death in Arabidopsis thaliana. Radhika gave a lucid presentation of her work on hypersensitive cell death and the involvement of both nitric oxide and hydrogen peroxide. This was, perhaps, the best seminar of the meeting.
The great strengths of the BSPP Presidential Meeting were the diversity and quality of presentations. The meeting did not dwell overly on matters molecular, or mycological, but rather produced an interesting and varied mélange that covered the kingdoms, and all aspects of the host-pathogen interaction. The meeting did well to cover its subtitle "Understanding mechanisms of resistance and pathogenicity for disease control". Signalling processes were considered at the whole organism level, but also at the molecular level and a number of signalling pathways were dissected. Notable in this respect were Nick Talbot's presentation on the MAPK/cAMP pathway in Magnaporthe grisea, and John Turner's discussion of the Arabidopsis jasmonate-signalling pathway in powdery mildew resistance.

No plant pathology meeting would be complete without consideration being given to the evolution of disease resistance. Richard Michelmore provided us with an erudite explanation of current thinking on the evolution of resistance gene clusters. Cutting edge considerations of pathogenicity were given by Ian Toth; detailing the first report of cDNA-AFLPs applied to bacteria. The potential for this technique seems vast.

The 2000 BSPP Presidential Meeting was a full, interesting and informative meeting, and a fitting end to Professor John Mansfield's time as the President of the Society. Scientifically and socially, the days were well filled, and no doubt every delegate went home with new insights and a jaded liver. We would like to thank the BSPP for their travel grant, without which we would have been deprived of this interesting meeting.

Hannah Jones, Emma Perfect, Gemma priddey and Keith Stewart
University of Oxford