BSPP News Autumn 2001 - Online EditionThe Newsletter of the British Society for Plant Pathology
Number 40, Autumn 2001
Conference and Travel Reports
- Molecular Plant-Microbe Interactions 10th International Congress
- International Sclerotinia Workshop
- Modern Fungicides and Antifungal Compounds - 13th Reinhardsbrunn Symposium
- Diagnostics and Disease Control
- 8th International Workshop on Plant Disease Epidemiology
Madison, Wisconsin, USA : July 10 - 14 2001
Almost 1000 conference delegates converged from all points of the globe to attend the MPMI meeting at Madison in July 2001. The location of the conference was superb; a waterfront lecture theatre and meeting place within the University Union building. All this set against a backdrop of oak-lined, flower-bordered streets guarded by timber-boarded houses nestling between tall brick or stone buidlings. Enough prose, what of the science?
As first time visitors to an international conference we had a mixture of fear and exhilaration. We had both read the web page, gasped at the registration fee (relaxed a little when realised it was in dollars!) and had even tackled the write-your-poster-abstract online! We then knew this was no ordinary conference but a post-millennium hi-tech intercommunication forum. Indeed we were not disappointed! At the reception drinks there was a buzz! People not only thirsty for the tasty local ale but to meet and extract as much information out of tired well-travelled fellow pathologists.
The seminars began with David Baulcombe, the keynote speaker, giving an interesting talk on the use of gene silencing as a way to dissect disease resistance. Over the next four days the talks were diverse in content. From Paul Schulze-Lefert's molecular-based presentation on the importance and function of barley's Mla locus in it's resistance to Blumeria graminis, to Nick Talbot's biochemistry-based seminar on the intricacies of turgor generation in appresorial development in Magnaporthe grisea. Richard Michelmore gave a thought provoking talk on the evolution of resistance genes as did Jan Leach when she showed a correlation between pathogen fitness factors and plant resistance gene durability. Barbara Valent gave a very stimulating seminar on the interaction between the rice resistance protein, Pi-ta, and the corresponding M. grisea avirulence protein, AVR-Pita, and when we were just thinking that E. coli was a glorified laboratory reagent, Nicole Perna put us straight showing amongst other things, the complete genomes of a deadly and harmless E. coli strain and the large amount of sequence homology that exists between them!
Apart from the seminars the food was also an eye-opener. As scientists who wholeheartedly supported GM food (and had each day attended seminars where we assumed the application of their research was to produce GM plants) we were rather amused that the majority of the food supplied was from the Organic range! It was delicious all the same, in particular the amazing range of cheeses for which, we found, Wisconsin is famous. There were over 600 posters, and every night each room reverberated with questions and discussions. On the final evening we attended a posh banquet dinner that was followed by music provided by the talented Phat Phunction and everyone merrily bopped the night away.
Jane Byrne and Lucy Nott
The MPMI conference provides a brilliant opportunity to keep in touch with the latest research achievements in different areas of plant-pathogen and plant-symbiont interactions.
The keynote lecture by David Baulcombe on dissecting disease resistance using gene silencing aroused a lot of interest. The ability of viruses to activate RNA silencing has been exploited in his laboratory as a system for dissection of other disease resistance systems in plants. Virus vectors have been constructed to carry fragments of host genes so that RNA silencing in the infected plant is targeted against the corresponding host RNA. Disease resistance in this virus vector-infected plant is reduced if this RNA encodes a protein required for disease resistance.
Vicki Vance gave a related talk on suppression of RNA silencing in plants using the helper component proteinase (HC-Pro) of potyviruses. Several cellular proteins that interact with HC-Pro in the yeast two-hybrid system have been identified. Experiments to over-express or knockout expression of these proteins are providing clues about the regulation of gene silencing in plants.
A series of talks were devoted to local/systemic resistance. Cross-talk between salicylic acid (SA)- and jasmonic acid (JA)-dependent signalling pathways is thought to be involved in fine-tuning of the defense reaction, leading to an optimal mix of defense responses to resist the intruder. Previously it has been demonstrated that there is no significant cross-talk between JA-dependent induced systemic resistance (ISR) triggered by non-pathogenic rhizobacteria, and SA-dependent SAR, triggered by necrotizing pathogens, since simultaneous activation of ISR and SAR results in an enhanced level of protection. However, in other cases SA- and JA-dependent pathways interact negatively.
Jan Leach presented a very interesting talk on pathogen fitness penalty as a predictor of durability of disease resistance genes. This hypothesis has been tested in the field and laboratory by studying interactions between Xanthomonas oryzae pv. oryzae (Xoo), the bacterial blight pathogen, and rice cultivars near-isogenic for different R genes. Adaptation of Xoo to virulence on rice with the Xa7 gene for resistance was associated with a cost in fitness, whereas there was no measurable fitness penalty for adaptation to rice with the Xa10. Although the proportion of strains with partial loss of avrXa7 function has increased significantly in the pathogen population over 12 cropping seasons, disease incidence on rice with Xa7 remains low.
An overview on comparative analyses of enterobacterial genomes was given by Nicole Perna. It is amazing how many differences are in the genome organisation of even such closely related organisms as two strains of Escherichia coli: harmless laboratory strain K-12, and a deadly enterohemorrhagic strain O157:H7.
Michael Gribskov gave us a chance to look into the future showing the scale of bioinformatics application in functional genomics and giving advice on how to cope with a 'tsunami' of experimental data.
Most of the world's main research groups working on Oomycete plant pathogens were represented at this Congress. Sophien Kamoun presented work on functional genomics of Phytophthora-plant interactions. His group has a very productive collaboration with David Baulcombe on using the recently developed Agrobacterium binary PVX vector for functional analyses of pathogen genes at an unprecedented high throughput rate.
After MPMI I attended the Oomycete Genetics 2001 symposium in Wooster, Ohio, hosted by Sophien Kamoun, giving me an extra chance to see the progress made in studying Phytophthora infestans, P. sojae, and Peronospora parasitica.
I would like to thank BSPP for providing me with the financial support to attend this very interesting and useful conference.
Scottish Crop Research Institute, Dundee
With 628 submitted abstracts at this meeting (see http://www.plantpath.wisc.edu/mpmi), there was plenty to get through. Talks were held in pleasant, air-conditioned auditoria - fortunate, given the cloudless skies and blazing sunshine we enjoyed throughout the conference. The main lecture theatre was conveniently located beside Monona lakeside terrace, a favourite spot for 'networking', if the number of delegates equipped with sunglasses and beer was anything to go by.
In the cell biology session, Sondra Lazarowitz (Cornell University) began by describing her work on the geminivirus movement proteins NSP and MP, which interact to move the viral genome from its site of replication in the nucleus to the cytoplasm and across the cell wall. NSP was shown to be responsible for export from the nucleus, and MP for movement across the cell wall. This was followed by a lavishly-illustrated presentation by Stephen Paddock (University of Wisconsin), who explained the use of fluorescence probes in multi-colour confocal imaging. Although in this case the colour patterns of butterfly wings were used as an example, these techniques are applicable to a broad variety of systems.
Raffaella Carzaniga (IACR - Long Ashton) spoke of a novel technique for the detection of melanised pathogens in plant tissues. Melanins are important to a variety of pathogens for both survival (protection from uv, free radicals, etc.) and pathogenicity. Precise information on the location of melanins within fungal cell walls has not previously been available. Raffaella described how, although melanin extraction involved a harsh process, it was possible to produce phage display antibodies to a precursor (1, 8-dihydroxynapthalene). These also bound to naturally-occurring melanin isolated from Alternaria alternata cell walls (but not other phenolics tested), suggesting that epitopes remain accessible in polymerised melanin. Melanin was shown to be restricted to the primary cell wall in A. alternata, implying precise spatial regulation.
Ton Bisserling concluded the session with an engaging and lucid talk describing his work on the rhizobial infection process. As he explained, the sophisticated infection mechanism, involving the curling of root hairs and subsequent formation of infection threads, implies that the colonizing rhizobia provide positional information to the root hair. He used fluorescence correlation microscopy to localise and quantify rhizobial Nod factors, and showed their accumulation in the cell wall, where mobility was reduced - consistent with the hypothesis that locally secreted Nod factors can provide positional information. Infection thread initiation and growth in the root hair was shown to be under the control of the host, the latter step in pea involving Sym2, which acts in a Nod factor structure dependent manner. The region orthologous to Sym2 in Medicago truncatula contains several genes encoding putative receptor kinases and LRR domain containing proteins. Their function in a negative control mechanism was explained: although negative dominant mutation altered host specificity, positive dominants did not increase host range.
At the close of the conference there remained only time to don the glad rags and head for the banquet and dancing, where a number of senior scientists could be found in an advanced state of refreshment. Not only did attending this conference give me an up-to-date summary of work new to me, as well as areas of previous interest, but it also provided the opportunity to discuss my results with others in the field, to mutual benefit. My one minor criticism was that the arrangement of the concurrent sessions meant that presentations of particular interest to me occasionally overlapped, but the only solution would have been a much longer conference. Mind you, I doubt there would have been many complaints.
University of Sheffield
My research interests focus upon durable resistance in wheat to the obligate biotrophic fungus yellow rust (Puccinia striiformis). Although there was nothing on this particular pathogen, there were studies on powdery mildew interactions with a range of hosts and a few posters on wheat leaf rust interactions. I will therefore concentrate on information about resistance genes.
A high standard was set with the opening speaker, David Baulcombe, who gave a well presented talk about virus induced gene silencing (VIGS) to dissect disease resistance in plants. VIGS are being used by a number of other groups to investigate down stream signalling in plant-microbe interactions.
Talks by Jonathen Jones, Paul Shculze-Lefert and Roger Innes looked at known resistance genes with the aim of discovering what signalling mechanisms these genes initiate. Many resistance genes require other genes for signalling to occur - this may be a reason why so few direct interactions between resistance and avirulence genes have been observed. Jonathan Jones suggested a model where Avr2 binds Rcr3 (Cladosporium fulvum), then this complex is recognised by Cf2 (tomato); here Rcr3 is acting as a 'guard'. Paul Shculze-Lefert proposed a model where ubiquitin-dependent removal of cell death protectants is required for Mla resistance in barley. Roger Innes suggested a model for RPS5 protein (Arabidopsis) function; such NBS-LRR type proteins may act as chaperones to 'guard' the targets of pathogen effector molecules.
Shunyuan Xiao and Brian Staskawicz discussed the ability of resistance genes to be transferred to different plant species and retain functionality; one of these, RPW8 (Arabidopsis) confers broad-spectrum resistance to distinct powdery mildew species. Giulia De Lorenzo talked about the possibility of engineering the primary structure of polygalaturonase-inhibiting proteins (PGIPs) to generate novel recognition specificity's to protect crop plants against pathogens, whilst on a similar tack Barbara Valent suggested the Pi-ta genes could be engineered to identify virulent AVR-Pita alleles.
Gene chip analysis was discussed by Andrew Bent and Jane Glazebrook. Andrew Bent is comparing four different R/avr pairings in Arabidopsis with Pseudomonas syringae and Jane Glazebrook is looking for genes effecting signalling by observing the expression profiles from Arabidopsis mutants with altered resistance's to P. syringae. So far, they have found data from gene chip analysis to be reliable.
Jan Leach talked about whether a fitness penalty imposed on a pathogen, when it tries to overcome a resistance gene, will make that resistance gene durable. Their studies with Xanthomonas oryzae and rice cultivars, near-isogenic for different resistance genes, agreed with this prediction.
I concentrated on posters involving gene expression studies. There were a number of techniques covered, including cDNA-AFLP, Microarrays, Suppression Subtractive Hybridisation, Representational Difference Analysis, Differential Display PCR and Single Pass Sequencing. These techniques have identified hundreds of up and down regulated genes during pathogen attack. The genes identified are from both the host plant and the pathogen. Many genes are unique. Known genes are involved in a range of processes from general housekeeping, stress and pathogen-induced, through to involvement in photosynthesis. It will be interesting to see how investigations into the functions of some of these genes progresses and if any of this information will help identify down-stream signalling processes during plant-microbe interactions.
I would like to thank the BSPP for awarding me a travel grant. I was able to meet many new faces and discuss new technologies and concepts in plant-microbe interactions, at this prestigious worldwide gathering.
John Innes Centre, Norwich
My colleagues and I are currently characterizing the genomes of Erwinia carotovora subspecies atropseptica (Eca) and Erwinia carotovora subspecies carotovora (Ecc), with a view to identifying new pathogenicity gene candidates. Therefore this report focuses on progress on both genomics of bacterial phytopathogens and Erwinia pathogenisis.
Complete genome sequences were announced for Ralstonia solanacearum, Agrobacterium tumefascians; Xanthomonas axoponodis pv. citri and Xylella fastidiosa (grape pathogen strain). Completion of the following sequences is imminent: Xanthomonas campestris pv. campestris; Leifsonia xyli (sugarcane pathogen) and Pseudomonas syringae pv. tomato DC3000. Previously only X. fastisosa (citrus pathogen strain) had been sequenced and so major progress has been made. Erwinia spp. are conspicuous by their absence from this list.
Analyses must follow sequencing. Comparative genomics will reveal much about the make-up and evolution of plant pathogens. Preliminary genome comparisons of the xyllelas and xanthomonads were presented. For P. syringae and R. solanacearum bioinformatic and / or mutational screens for "hrp box" regulatory motifs were performed. In both cases several genes (other than the usual set of hrp genes) were found to carry this motif and therefore these may encode hrp-regulated Type III secretory system effector proteins (TTSEs). At this stage it is worth mentioning that new evidence confirms the (long supposed) model of translocation of TTSEs through the hrp pilus directly into host cells.
Much new progress was reported for Erwinia, despite the lack of a sequencing project. Preliminary genomic data has emerged from here at SCRI and from Nicole Perna (Madison). Perna obtained 2000 sample sequences from the E. chrysanthemi (Ech) genome. The findings imply that around 39 % of Ech sequences (1.5 MB) are not present in E. coli. Comparative genomic studies within the Enterobacteriaceae are leading to an emerging model of a shared "backbone" but with large areas of inter-species differences. Surprisingly, Ech sequences included some similar to sequences involved in auxin and phytotoxin synthesis and opine catabolism in unrelated species. Some similar sequences were also identified in Eca here at SCRI.
Steve Beer's group (Cornell) reported much new work, including the first use of signature tagged mutagenesis in a phytopathogen (E. amylovora), giving 79 mutants with reduced virulence. Other studies included characterisation of ORFs around the E. amylovora hrp cluster and evidence that some are hrp-regulated (hrp-boxes again!) and encode TTSEs. Eleven hrp-secreted proteins were found by 2D electrophoresis. One such protein is DspE, which was shown to possess nuclear localization signal motifs and to localise in the nucleus when (artificially) introduced into onion cells.
Noel Keen (UCR) presented microarray data from Ech, obtained by using subcloned random genome fragments as array elements. Fragments showing differential gene expression in vitro cf. in planta were sequenced. Despite the problems of this approach compared to defined microarrays, data obtained suggested up-regulation of candidate pathogenicity genes, iron acquisition genes and genes that may protect against plant response oxidative stress.
More light was shed on the complex regulation of production of plant cell wall-degrading exoenzymes in Ecc, by Hyytiäinen et al. (Helsinki). They described the central role of expAS (required for exoenzyme production) and kdgR (repressor of exoenzyme production).
An Israeli group (Nizan-Koren et al.) and David Coplin's group (Ohio) have partially elucidated hrp regulatory cascades in E. herbicola pv. gypsophilae (Pantoea agglomerans) and Pantoea (Erwinia) stewarti pv. stewartii respectively. Both groups found that HrpY must be phosphorylated to upregulate hrpS. This in turn activates transcription of hrpL whose product is thought to bind to hrp boxes, thus promoting transcription of TTSEs. Phosphorylation of HrpY could be mediated by HrpX (a sensor kinase) but this does not happen in host plants and so an unknown in planta phosphorylation signal is presumed to be involved in triggering the cascade.
As well as exoenzymes and TTSEs, attachment may be an important factor in Erwinia pathogenesis. Alan Collmer and co-workers (Cornell) elegantly demonstrated (with gfp-tagged bacteria) how hecA (which is similar to haemolysins from animal pathogens and was recently identified in Eca by us at SCRI) is necessary for Ech for both attachment to leaves and for autoagglutination. Autoagglutination was required for effective maceration of the host cells, perhaps by allowing effective quorum-dependant signalling. Michael San Francisco's group (Texas) showed that Ech possesses an outer membrane protein (OMP), similar to intimin (required for attachment of enteropathogenic E. coli strains to gastrointestinal cells), that is a putative attachment factor. They also described another Ech homologue of an E. coli OMP, tolC. Mutants of tolC show reduced maceration and tolC may mediate efflux of host cell defence factors from the pathogen.
Posters by both Venisse et al. (INRA) and Beer's group showed data on altered gene expression in apple plants challenged with E. amylovora. The former group used cDNA-AFLP to compare compatible and incompatible interactions whereas the later group sequenced clones from a cDNA library that was screened for changes in regulation, post-inoculation in a susceptible reaction.
Intriguing data emerged from both sides of the E. amylovora - P. agglomerans interaction, where the latter can reduce incidence of fire blight caused by the former. Vanneste et al. (Hort Research, New Zealand) showed that this antagonism is in part due to a small peptide antibiotic from P. agglomerans. E. amylovora was found by Burse and Ullrich (Marburg) to possess mdeE which encodes a multidrug efflux protein that helps relieve inhibition by P. agglomerans, possibly by providing protection from antibiotics.
I would like to thank the BSPP for their generous support, which allowed me to participate in the most interesting meeting I have yet attended.
Scottish Crop Research Institute
A good presentation of the fungal side of the interaction was given in the III plenary session entitled "Plant-Fungal Interactions". Pierre de Wit opened the session with a most compelling and very clearly presented seminar on the molecular basis of co-evolution between Cladosporium fulvum and tomato. The cloning and characterisation of two new avirulence genes, AVR2 and AVR4E, were demonstrated. In addition, comparison of the resistance genes Cf-4 and Cf-9 by swaps and directed mutagenesis resulted in identification of domains that are essential for function and specificity towards AVR4 and AVR9, respectively. Results suggest that specificity is determined by only a few amino acids within the LRR domains of the Cf-4 and Cf-9 proteins.
Another thought-provoking and convincing lecture came from Barbara Valent, who showed evidence for the first report of a direct interaction between the newly isolated AVR-Pita from Magnaporthe grisea and the corresponding resistance gene Pita in rice, which, in contrast to most of the previously examined cases, takes place inside the plant cell. The latest model raised interesting questions on the nature of the plant-fungal interface for intracellular infection hyphae and on the mechanism by which the fungus delivers proteins into the cytosol of healthy plant cells. Remaining on the same theme, directed evolution of Pi-ta to recognise naturally occurring avr-pita- alleles leading to an immediate impact on Pi-ta efficacy in the field was discussed too.
The first cloned gene from Brassica nigra conferring resistance to the blackleg fungus Leptosphaeria maculans was reported by Christina Dixelius, whereas Nancy Keller went back to chemistry, by reporting progress on the lipid-mediated signaling in the Aspergillus/seed interaction. After the morning coffee, we continued with Maria Harrison demonstrating the power of EST sequencing and expression profiling in an attempt to document the molecular changes occurring in the roots of Medicago truncatula during development of the symbiosis with Glomus versiformae. Thomas Boller put some more emphasis on investigating the recognition of "non-self" in plants, by analysing a similarly sensitive and specific perception system for a molecule called flagellin, characteristic of bacteria. It was found out that, once again, an LRR protein was responsible for the binding of the elicitor.
Nick Talbot gave the final talk of this session, a stimulating account on the process of appressorium-mediated infection in Magnaporthe grisea. More specifically, since the appressorium turgor is due to accumulation of glycerol, by studying the contribution of glycogen, lipid and trehalose to glycerol generation, he came up with a working model for the turgor generation and the cuticle penetration.
John Innes Centre, Norwich
Friday's afternoon session concerned secretion of avr/vir factors of nematodes and bacteria. Hans Helder gave a very interesting talk on the identification and function of potato cyst nematode secreted proteins during pathogenesis. Comparison of mRNAs from five developmental stages was compared by cDNA-AFLPs. Forty primer combinations gave rise to 4,500 TDFs (transcript-derived fragments), from which a number of TDFs were up-regulated in the only infective stage of the nematode. This strategy leads to the discovery of several putative pathogenicity factors used by the infective juvenile to penetrate and migrate inside the plant root. Three b-1,4 endoglucanases, a pectate lysate and a xylonase were identified. All the above proteins have their highest homology with genes from bacteria, which makes a strong case of horizontal transfer from bacteria to nematodes.
Yuwei Shen from University of California Davis, talked on the isolation of genes from races of Xanthomonas oryzae pv. oryzae that are required for the AvrXa21 activity on rice lines containing Xa21, a receptor like kinase. Tn5 mutagenesis of the avirulent strain PR6 leads to the identification of two genes raxPQ, which are similar to NodPQ from S. meliloti. raxP and raxQ encode an ATP sulphurylase and adenosine -5'-phosphosulphate (APS) kinase that function together to produce active forms of sulphate, APS and PAPS (3'-phosphoadenosine-5'-phosphosulphate). Interestingly, mutants PR6DraxP and PR6DraxQ lost the ability to produce APS and PAPS. A genomic clone (10.78) from avirulent strain PR6 was able to complement KR1 (virulent strain). Three ORFs, raxST, raxA and raxB, are required for avirulent activity in transconjugant KR1(10.78). RaxST contains sulphotransferase signature domains, whereas RaxA and RaxB are similar to components of the Type I secretion system: a membrane fusion proteins and an ABC transporter.
Sheng Yang He then gave an account on some interesting results on secretion of Type III effector proteins and on responses that overcome a salicylic acid-mediated Arabidopsis response. In situ immunogold labelling of HrpZ suggested that secretion occurs adjacent to the pilus. In an interesting experiment involving uncoupled expression of AvrPto, Seng Yang He's lab was able to show that secretion occurs from the tip of the pilus. A DC3000 hrp mutant carrying a large deletion in the conserved effector locus (CEL) that contains avrE, orf2, orf3, orf4, hrpW and orf5, although eliciting an HR on tobacco, was not able to cause disease in wild type Arabidopsis plants. Interestingly, the same mutant was able to cause disease in NahG plants (defective in salicylic acid-mediated host response). Complementation studies revealed that orf3 and orf4 encoding 18kDa and 65kDa proteins were responsible for the CEL mutant phenotype, respectively. A yeast-two-hybrid analysis showed that Orf3 and Orf4 interact indicating a chaperone role for orf3.
Ulla Bonas gave the last talk of this session. avrBs3 an avr gene from Xanthomonas campestris pv. vesicatoria was immunolocalized in pepper leaf section. Ulla's lab adopted a cDNA-AFLP strategy to isolate and identify Type III effector proteins in X.c. pv. vesicatoria. This interesting approach leads to the isolation of XopA (Xanthomonas outer protein) which is secreted via the Type III secretion system and has homology with psvA, a virulence factor from P. s. pv. eriobotryae, and XopB which shares homology with avrPphD.
Pseudomonas syringae workshop
On July 9th, a workshop was held focusing on Pseudomonas syringae, before the start of the official MPMI program. The workshop was attended by approximately 40 people from a wide range of countries. It was organised by Sheng-Yang He and he opened the session by stating a set of four objectives that he felt were the key areas that the P. syringae community need to be address. These were: 1. Attempt to identify key unresolved questions regarding P. syringae biology (from virulence/avirulence mechanisms to population genetics), 2. Discuss and possibly standardise key experimental procedures, 3. Define the essential aspects of a user-friendly and central plant-P. syringae functional genomics database, 4. Raise issues/questions about current and alternative mechanistic models regarding various aspects of P. syringae biology. There then followed speakers who each gave brief overviews and led a discussion of one area of interest of P. syringae research.
Susan Hirano started with an overview of P. syringae biology in the field (ecology, epidemiology, epiphytic growth). She talked about the populations dynamics of P. syringae in the field and posed questions such as what causes changes in population size over a growing season and what triggers disease to develop? This generated much discussion and highlighted how little we know about the basic biology of this pathogen.
The next overview on avirulence genes was a double act by George Tsiamis and myself. I discussed the current state of our knowledge about the avirulence genes in the pathovars our two groups work on and asked whether we needed to keep on isolating more avirulence genes (the answer from the group was yes) and do we understand the mechanisms by which these genes may be moved around (the answer was no!). George then described "mining" the recently deposited P. syringae pv. tomato strain DC3000 genome sequence. He used the conserved promoter sequence of avirulence/virulence genes to predict the presence of approximately 129 of theses genes in the genome. The audience felt that this was an over-generous prediction and this led to a lot of discussion of how many there might be. It also generated discussion about naming of predicted ORFs and ORFs that then go on to be shown to have a function. The general consensus is that this is going to get very complicated as more genomes are sequenced and needs to be given some serious thought.
Jim Alfano and Carol Bender then gave an overview of virulence systems. Jim concentrated on reviewing aspects of the type III secretion system and suggested a future priority should be to look for secretion signals of the effector proteins. Carol summarised toxins and hormones and suggested we need to be looking at their plant targets. Finally, an overview of host responses was given by Barbara Kunkel who discussed what determines a host response to invasion by a pathogen, for example what are the limiting factors inside the host plant to pathogen growth.
After lunch Alan Collmer talked about the DC3000 functional genomics project which has been responsible for sequencing the DC3000 genome and analysing the data generated. Alan is developing a web site (PPI: Pseudomonas-Plant Interaction) that he hopes will be used as a community-wide resource for Pseudomonas research and will include amongst other things a repository of published data, a bulletin board, bioinfomatics resources and standardised protocols.
Shen-Yang He then concluded by saying that the idea of bringing the P. syringae group together was "to maintain individual creativity while helping each other". This was a very successful workshop generating a lot of discussion, making people who work in one specific area think about other aspects and posing a lot of questions for the future.
University of the West of England, Bristol