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Autumn 2009 Meeting Reports from the XIVth International Congress on Molecular Plant-Microbe Interactions, Quebec 2009
The 2009 MPMI meeting was held in the delightful Quebec City, which cascades over a cliff down to the St Laurence River. It’s pretty winding lanes are reminiscent of old European cities (though extremely clean!). The streets are dotted with cafes and the food is very French, i.e. delicious, with moose and other local specialities added to the mix. The meeting took place in the ‘Centre des Congras de Quebec’ which is very close to the stunning historic walled section of Quebec City, which has been a UNESCO world heritage site since 1985. With large windows and a hill-top position delegates could see views across this historic city, whilst experiencing concurrent and plenary sessions in comfortable seminar rooms. Approximately 1000 participants registered to attend the conference. Nearly 140 talks, the majority in concurrent sessions, and 700 posters from 18 categories were presented. The main scientific topics were diverse and included pathogenic interactions, symbiotic interactions, common host mechanisms, signalling and molecular dialogues, dynamics of plant responses to microbes, plant-microbe interactions and technology transfer, ecology and evolution as well as plant immunity.
A number of BSPP members attended the meeting and here are edited reports from some of these members:
The meeting was opened by Luis Sequeira (University of Wisconsin) who in his talk entitled ‘Facing the issues in agricultural biotechnology’ stressed the need for ‘translational research’ to control plant diseases. The IS-MPMI award for outstanding and innovative research was presented to Jeff Dangl (University of North Carolina) who, after Thomas Boller from the University of Basel, is the second scientist to be awarded this prestigious prize.
Among the many fantastic presentations at the conference two talks from the laboratory of Brian Staskawicz gave an interesting insight into the molecular mechanisms of plant disease resistance. The first talk was presented by Ksenia Krasileva and focused on the interaction between the Arabidopsis resistance protein RPP1B and the cognate Hyaloperonospora arabidopsidis effector ATR1. Evidence for a potential direct interaction between ATR1 and RPP1B was presented. Furthermore, Ksenia showed that RPP1B localises to the cytoplasm and the nuclei. However, the nuclear localisation appears to be dispensable for ATR1 recognition and the signalling leading to the hypersensitive response upon effector detection, suggesting that RPP1B is involved in two different signalling pathways. Brian Staskawicz’s talk focused on the Xanthomonas campestris pv. vesicatoria effector AVRBs2 that is specifically recognised by the pepper resistance protein Bs2. It appears that the recognition event perturbs the bacterial type III secretion system and other effectors such as XopX are no longer delivered. Thus, this talk gave an insight into a potential order of effector delivery and also an interesting mechanism of resistance that could target the bacterial effector delivery system.
Julio Vega-Arreguin from Peter Moffett’s laboratory at the Boyce Thompson Institute for Plant Research presented an interesting poster on the mechanism of non-host resistance found in Nicotiana edwardsonii towards Phytophthora capsici. The poster, entitled ‘Non-host resistance against P. capsici is mediated by both R gene and basal defence mechanisms’, showed that the P. capsici AVR3a homologue originally identified in P. infestans and known in P. sojae as AVR1b, elicits an HR in various Nicotiana species. Virus induced gene silencing studies demonstrated that non-host resistance is mediated by members of the I2/R3a resistance gene family and yielded N. edwarsonii plants with increased susceptibility towards P. capsici.
I presented a poster entitled ‘Exploiting the P. infestans genome to determine targets for sustainable potato protection’ that focused on P. infestans AVR3a in a case study to identify more durable blight resistance. Our strategy relies on the identification of secreted, invariant and functionally essential (and thus non-redundant) effectors that, as the pathogens ‘Achilles heel’, yield resistance that is more difficult to overcome by pathogen variants. Stable gene silencing in P. infestans has shown that some conserved effectors, including Avr3a, are functionally non redundant.
Indeed, silencing Avr3a results in a complete loss of pathogen virulence on normally susceptible potato and N. benthamiana plants. However, this phenotype can be complemented by Agrobacterium-based expression of Avr3a in N. benthamiana prior to infection which subsequently restores full pathogenicity. A screening of the Commonwealth Potato Collection (CPC) has identified potato accessions that recognise both known alleles of AVR3a and display good resistance to diverse blight lineages.
Ingo Hein, SCRI
Needless to say the emphasis on translational agricultural research in Luis Sequeira’s opening address was heartening for those of us who work on crop plants. The application of translational research was immediately obvious in Pierre de Wit’s talk on the tomato pathogen Cladosporium fulvum and a search for effectors homologous to its effectors among the Dothideomycetes. A surprising outcome of the study was that an Avr4 homologue from the banana pathogen Mycosphaerella fijiensis was recognised by the tomato resistance protein Cf-4; providing a route to generating resistant bananas that otherwise contain no R genes to M. fijiensis. Nick Talbot followed with a typically spectacular talk dissecting the requirements for Magnaporthe appresoria formation.
We noted an increase in the number of people discussing pathogen effectors at this MPMI. Regine Kahman talked about Ustilago maydis effectors required at different stages of infection. Peter Dodds described studies in collaboration with Adrienne Hardham on effector translocation, noting that the signals seemed to be quite divergent. Frank Takken described a double-barrelled approach to the host-pathogen arms race by Fusarium oxysporum, evasion of recognition by point mutations in Avr2, or co-expression of Avr1 which blocks the recognition of Avr2 by I2 (among other Avr/R pairs). One of the presentations that had many people talking was that of Ulla Bonas describing the transcription factor effector AvrBs3 which contains a region of 17. 5 repeats of a 34 amino acid sequence involved in binding to UPA boxes. Notably, one of the genes that contains the UPA box is the cognate R gene Bs3. The Bonas group discovered that there was a code relating the amino acid sequence to the nucleotide sequence of the UPA box; each pair of amino acids had a marked preference for certain nucleotides. This allowed them to predict target UPA boxes for given amino acid sequences and to create artificial UPA boxes which they fused to a GUS reporter and showed specific activation of expression by different AvrBs3 homologues. This work and also that presented by T. Lahaye indicate potential utility of UPA boxes (fused to defence genes) for resistance strategies.
Barbara Mauch-Mani presented work exploring the link between ABA and resistance and revealed that in the course of their studies they found that light levels had a significant effect on resistance, with high light levels increasing callose production in response to flg22 and chitosan. For those of us working in the far north this has implications for how our results may differ markedly between the dark winters and the very long days of summer.
I presented a poster entitled ‘Evolutionarily distinct RXLR effectors from distantly related oomycetes target the plant exocyst’ describing some exciting new results from the SCRI Phytophthora group in collaboration with Jim Beynon’s group at Warwick University HRI. Our yeast-2-hybrid (Y2H) analyses have shown that the Phytophthora infestans effector AVR3a and diverse RXLR effectors from Hyaloperonospora arabidopsidis interact with homologues of Sec5 (a component of the exocyst vesicle tethering complex involved in trafficking between Golgi and the plasma membrane) indicating that it is a pivotal target for oomycete pathogenicity. Using fluorescent protein tags, we demonstrated that Sec5 localised to small mobile vesicular bodies and the cytoplasm that accumulate around haustoria during infection. One of the possible reasons for the targeting of the endo- and exocytic pathways by pathogens is the disruption of receptor-mediated signalling; the endocytic recycling of membrane receptors, such as FLS2 (Robatzek et al. , 2006), is thought to be an essential step in their signalling pathways. Linking to this was the poster of Vossen and Joosten in which they provide further evidence of the role of endocytosis in resistance signalling.
They showed that Cf resistance receptor proteins of tomato contain a tyrosine based endocytosis signal and that this motif is essential for the Cf protein interaction with m-adaptins in yeast-2- hybrid. Cf mediated resistance was also compromised after silencing the madaptins C and D.
A couple of other posters piqued my interest due to their relevance to our work. Mukhtar et al. from the Dangl lab in collaboration with M. Vidal describing some of the results of the matrix-2- hybrid screen in which Pseudomonas syringae type III effectors from different strains and various receptor types, were tested against 9,500 cloned Arabidopsis ORFs. The poster gave an overview of the interactome showing major categories of interactors including transcription factors (16% of interactors found), enzymes (17%), and F-box proteins. As with our much smaller scale study their results included examples “of Arabidopsis proteins targeted by multiple type III effectors” but in addition they found interactions of these targets with receptor proteins, which we have not yet looked into.
Schipper et al. from the Kahman lab focussed on one of the effectors mentioned in Regine’s talk, Stp1, and the poster contained some nice plasmolysis results showing the effector in the apoplastic space between the host and pathogen. Their plasmolysis solution, 1 M NaCl might be a bit brutal for Nicotiana benthamiana or potato (they used maize), but their images have further encouraged me to try plasmolysis with some of our transgenic P. infestans although with alternative solutions.
Ingo and I, very grateful for the BSPP support and wanting to do our little bit for the society, spent some hours at the BSPP stand telling anyone who paused what a great society it is, handing out the high quality freebies and past issues of BSPP journals and seeing who could fly the cute MPP foam planes the furthest.
The final party saw some enthusiastic dancing by the likes of Murray Grant, Volkan Cevik and Antonio Molina that began in the conference hall and continued to the sounds of an 80’s tribute band in a nightclub with the largest disco ball we had ever seen. The music at the conference party was provided by a local Quebec family group who mixed some virtuoso musical talent with vigorous clowning, and woodcutting! The latter was surreal but I guess in a land full of trees and lumberjacks…
Paul (husband) and I took advantage of a few extra days in Quebec to go down the St Laurence River to the lovely village of Tadoussac where the population and variety of whales and dolphins has to be seen to be believed.
Petra Boevink, SCRI
My own particular interests meant that the plenary session on Common Host Mechanisms and Signalling and Molecular Dialogues on the Tuesday morning were particularly relevant. A number of the presentations were especially interesting. The first presentation of the morning was given my Jonathan Jones (Sainsbury Laboratory) on recent advances using pathogen effectors to understand host resistance mechanisms. The focus here was on the effectors of the downy mildew pathogen Hyaloperonospora parasitica and their role in non-host resistance. He presented recent data on genome sequencing and how this is providing insights into host deference mechanisms. This was followed by S-Y He from Michigan State University who presented work on Pseudomonas syringae pathogenesis in Arabidopsis.
Their studies of the molecular action of effector proteins and coronatine is revealing a fascinating array of host cellular functions associated with vesicle traffic, stomatal function, jasmonate signalling, and senescence-associated leaf chlorosis. The challenges ahead are how to disable these virulence factors for disease control. He also emphasised that, generally, people are studying effectors as individuals and their roles are likely to be more complex when we begin to look at them in combinations.
Roger Innes, Indiana University, also presented interesting work on the molecular mechanisms underlying pathogen recognition. The ‘guard model’ of effector protein recognition was proposed several years ago now but still little is known about the downstream signalling from this recognition that leads to plant resistance. Using ‘super’ bright CFP and RFP constructs they have shown changes in the subcellular location of resistance proteins before and after activation and are investigating this to see if it has functional significance.
A theme that seemed to be emerging though these sessions and indeed the congress in general was that the use of second generation high throughput sequencing techniques has moved on a lot since the last IS-MPMI meeting two years ago. At that meeting, the sequences were only really just starting to be generated and there was a lot of talk about the technical difficulties on mining all the data that was being produced. Now we are seeing some really interesting biological insights coming out of all this information. For example, Brain Staskawicz gave a presentation on the recognition of pathogen effector proteins by NB-LRR immune receptors. This group is interested in using molecular breeding to develop durable resistance in agricultural crops. They are sequencing the genomes of a number of Xanthamonas vesicatoria genomes and have been using the data to look for conserved effector genes that may be essential for virulence of the pathogen.
They then use these genes as molecular probes to identify host targets controlling plant innate immunity and aim to use the identified resistance genes in plant breeding programmes. In these programmes the aim is to “stack” up the resistance genes in order to develop durable resistance. He finished with a question that even if this work produces new resistant plant varieties will they be economically viable in the current climate of mistrust of GM plants, which is a sobering thought.
Although the congress was quite intense, there was an afternoon boat trip including views of the Montmorency Falls, which are taller than the ones at Niagara, and a final banquet and show which was, well, interesting!!! I would like to thank BSPP for the financial support to attend this meeting.
Dawn Arnold, University of the West of England, Bristol.
In his introductory talk, Luis Sequira stressed the need to fulfil our (IS-MPMI) responsibility to look at agriculturally relevant problems rather then focus heavily on fundamental plant pathology. He highlighted the successes in securing funding for research in “translational” areas from governments and other sources, as exemplified by medical colleagues. His view was that a similar strategy should be mimicked by plant pathologists. He presented a cogent and provocative overview of topics such as: the status of biotechnology in developing countires; antagonism to GM in Europe; patenting in biotechnology; the “select agent’ issue; the food population issue; funding for agricultural research and the environmental costs of biotechnology.
This was a timely reminder at the very start of the meeting that the science, although crucially important, is conducted in a climate that is inextricably linked with policy issues, politics, economics, agendas, social structures and even religion.
In the quorum sensing session, Ann Hirsch presented work on the role of quorum sensing (QS) in Sinorhizobium meliloti with ExpR acting as a repressor of biofilm formation. Her evidence was that QS was important is the free living state rather than during nodulation. During this session there were also presentations on the varied roles of QS in Xanthomonas, Pantoea and in rice bacterial grain rot due to Burkholderia glumae. In the technology transfer session, Gonsalves gave a very impressive review of the “science and art” of developing a commercial product in agrobiotech. He used virus-resistant transgenic papaya as his case study and covered the key issues pertaining to the successful application of GM to a real life problem of economic, social and political import. Loper discussed the use of genomics and metabolic profiling systems to identify new bioactive secondary metabolites from Pseudomonas fluorescens strains potentially useful as biocontrol agents from suppressive soils. She highlighted the importance of bioinformatics interrogation searching for candidate NRPS and PKS sequences, and informed chemistry profiling. Belanger continued this biocontrol theme but with more emphasis on plant – pathogen interactions and antifungals. He brought home the salutary fact that exciting “novel” bioactive compounds are sometimes rediscovered from the literature of decades earlier, after a lot of expensive contemporary research!
In the biocontrol session, Hofte gave an overview of the roles of biosurfactants in Pseudomonas-mediated biocontrol. This also covered roles of phenazines and their effects on soil-borne fungi. Interestingly, these were from P. aeruginosa isolates from chickpea roots but the strains were not of direct use in agriculture because of the human pathogenic potential of this species. He highlighted the impacts of temperature on the regulation of such metabolites in P. aeruginosa and P. fluorescens.
Overall, this was a big and successful meeting with a wide spectrum of talks and a large hall full of posters on diverse topics. It had good hospitality and the venue was quite compact with easy access and movement between lecture rooms. Because the rooms all had flat floors it was occasionally less than ideal for viewing the lectures. The format of the meeting with the main plenary lectures in the mornings and specific sessions in the afternoon was standard for the MPMI Congress. The final banquet at the end of the meeting was a good ending to the meeting but seemed rather less impressive and engaging than in Sorrento or Merida.
This may have been, in part, because the after-dinner socialising, music and dancing was not generally indulged in to the same extent as in previous meetings. The somewhat bizarre procedures for alcohol purchase – and the prices (even for water) – may just have contributed to that!
George Salmond, University of Cambridge
My initial impressions were very good thanks to the location and atmosphere of Quebec and the dedicated conference venue and facilities. However there were some definite negatives. No hard copy abstracts were supplied (so who is really going to find time to locate and print out the ones you want, as suggested by the organizers?). On the same theme, if you were a dedicated attendee, there was insufficient time to think, sleep or eat. An 8 am start through until 21.30 or beyond for posters (650) with little time to grab food or contacts. Exhausting.
Scientifically the programme reflected the remarkable rate of progress, especially with pathogen effectors; the field is exciting and may hold keys to new pathways and resistances. Thus effectors tended to dominate; therefore and unfortunately, sometimes speakers’ expectations of the audiences were unrealistic. Many do work on other things! Some key points that were addressed included: Are effectors recognized in non-hosts or ineffective in these? Can we turn crops into nonhosts (J. Jones)? Effectors may be useful as molecular probes for novel sources of resistance, followed by stacking of resistance genes for durable disease control (B. Staskawicz). The Phytophthora infestans genome has just been published and reveals >450 RXLR effectors. It is clearly adapted to overcome resistance with its “plastic” genome, containing a high number of repeats, and enriched in secretory proteins and effectors. Also it has a larger genome (240 Mb) than other Phytophthoras, a mixed reproductive system, high potential gene flow, large population and high mutation rate (S. Kamoun). Effector expression and function is beginning to explain the biotrophy-necrotrophy switch (P. Birch).
Not everyone agreed, but I was pleased to have the inclusion of more applied aspects alongside the increasingly hardline molecular offerings. Trichoderma remains a big story as its beneficial effects go far beyond biological control, as plants clearly benefit from interactions with some selected isolates.
Over 100 “biofertilizer” products exist on the market and large scale production, especially in developing countries, was described by G. Harman. The development of GM control of papaya ring spot virus in Hawaii was enthusiastically described as an example of a success story by D. Gonsalves. Also he detailed the complex steps involved in registration, such as is currently ongoing for the Japanese market. Another worthwhile inclusion was the incorporation of other pathogen-host systems, such as invertebrate pathogens. However, I consider what was chosen was rather limited in its scope as much more is out there for a meeting such as this. One exception was an approach showing that bacterial plant pathogens appear to be adapted to survive in and be spread by predators such as nematodes, insect larvae and amoebae. Some of these anti-predation genes are being unravelled by F. Dorati in joint work involving universities of Reading, Bath and West of England.
Richard Cooper, University of Bath
The opening address by Prof. Luis Sequeira set a sobering tone – in 20 years of major advances in scientific understanding little progress has been made in the field at a “grass-roots level”, i. e. we have not provided the agricultural community with new and effective methods of disease control. Can we begin doing “translational research” as the medical community do? The charismatic Dennis Gonsalves also encouraged delegates to work harder at getting transgenic plant varieties to commercialisation. He warned, “don’t change your approach too often as timing is critical”.
So with our wrists firmly slapped we entered the plenary and concurrent sessions. With the last Congress’s focus being firmly on PAMPs and the Zig-Zag model, emphasis this year moved to RxLR motif-containing effectors and the search for other motifs, for example the CHxC and CxxC motifs of Albugo identified by J. Jones et al. Also widely discussed were the structures of active and inactive conformations of effector recognition proteins (R-proteins) carrying nucleotide binding domains (NB) and leucine rich repeats (LRRs) – NB-LRRs.
One of the plenary session highlights was Ulla Bonas’s lecture entitled “How Xanthomonas manipulates the plant cell”. This lecture in fact turned out to be the Congress’s version of The Da Vinci Code! The transcription factor and effector protein, AvrBs3, contains repeat regions of up to 30 amino acids (aa) with 16 repeats. The aa at positions 12 and 13 correspond to nucleotides in plant promoter motifs, e.g. if 12 & 13 are H & D then the plant nucleotide will be adenosine. Thus a code can be written to design both model boxes and artificial effectors. It is interesting that AvrBs3 targets promoters rather than the R gene encoded protein.
On Wednesday afternoon there was the chance to explore the 17th century theme park that is Old Quebec. For some Europeans the fortress walls and chateau may have looked rather shiny and new, however the quaintness and attractiveness is undeniable. Others were taken by boat to see Quebec from the Saint Lawrence River and also saw some impressive waterfalls.
The vast array of posters on show demonstrated the wide reach of the Congress’s appeal and relevance and the great interest caused the viewing times to be extended. From plants using metal ions for pathogen defence to a primitive form of the Type III Secretion system found in a P. syringae strain there were many new ideas and results to interest the delegates.
At the poster session my work on P. syringae hrp gene regulation led to some interesting discussions concerning a possible post-transcriptional regulation event on two of the proteins I study – HrpV and HrpG. These proteins are expressed from the same operon, and are therefore presumably at a 1:1 ratio, however HrpG negatively regulates HrpV. I will be exploring the timing of their expression using realtime RT-PCR as well as testing the strength of their binding when also in the presence of HrpS, an AAA+ enhancer binding protein, affected by HrpV.
Finally the conference ended with the closing ceremony where numerous awards and thanks were presented. Then it was the banquet with the final chance to talk to your favourite elusive researcher. With some delegates off on their summer holiday in Canada or the USA and others making their way home we all look forward to the XV Congress in Kyoto 2011.
Ellen James, Imperial College