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Molecular Plant-Microbe Interactions (MPMI) conferences take place every two years, and the 16th International Congress of the International Society for Molecular Plant-Microbe Interactions was hosted by the Agricultural University of Athens in Rhodes, Greece and co-organised by the Hellenic Phytopathological Society and the Hellenic Society of Phytiatry.
Over five days, 1100 registered participants from 55 countries, including reportedly nearly 400 research MSc or PhD students, attended the scientific program included seven plenary session, 32 different themed concurrent sessions as well as 3 evening poster sessions displaying over 750 posters. This made it immediately clear the massive amount of research taking place into plant-microbe interactions. There was an appealing choice as the program covered a wide range of topics and provided excellent opportunities for networking with many world leading researchers in this field. In addition, attendees of the congress celebrated the 20th and 30th anniversaries of the first cloning of plant immune receptor genes and first isolation of avirulence effector gene, respectively.
Below is a compilation of some of the highlights of the meeting as seen through the eyes of a number of these BSPP-funded participants, all of whom have expressed their thanks to the BSPP for partially funding their attendance at the Congress.
Laura Boyden, University of the West of England
I was particularly interested in talks discussing the motivation and long term goals of research into plant pathology. Brian Staskawicz discussed the importance of translating the research into disease resistance into marketable products to create durable resistance in the field. Xanthamonas perforans is responsible for Tomato Spot and is an important plant pathogen in the US, affecting 92% of growing areas in Florida and 40% in the US as a whole. He described his work surrounding the insertion of a resistance gene from pepper, Capiscum annum into tomato plants, conferring resistance to Xanthamonas perforans. I was particularly interested in his discussion on the importance of providing education to the general public regarding the use of genetically modified organisms as this is an important topic for all of us working in plant pathology. He suggested that perhaps the general public would be more comfortable with this system of inserting resistance genes from one popular crop into another. It was fascinating to hear this important subject discussed by one of the leading researchers in the field.
Many of the talks during the conference surrounded the mechanisms of pathogen associated molecular pathogens (PAMPS) which I found fascinating coming from a biomedical science and immunology background. I was able to draw parallels with the animal immune system and the host pathogen interface from my previous work. Cyril Zipfel’s talk centred around pattern recognition receptors (PRRs) and how they stimulate the downstream effects of the immune response. He gave an excellent overview of the work carried out so far into the progress made in elucidating the pathways involved in the plant immune response, in par ticular focussing on the phosphocode of early PAMP-Triggered Immunity (PTI) signalling. He pointed to recently published work from his lab which described the importance of PRR tyrosine phosphorylation. HopAO1, a tyrosine phosphatase from Pseudomonas syringae can reduce the phosphorylation of EF-TU RECEPTOR (EFR) thereby preventing a subsequent immune response. Better understanding of the negative regulation of PPR complex activity can contribute to work in the field, engineering the PTI response can be used for broad spectrum disease resistance in crops. Zipfel described the possibilities of transferring PAMP perception across plant families to generate this resistance. I thought this went well with the discussions from Brian Staskawicz’s talk regarding the insertion of resistance genes across plant families. I was interested to hear about the idea of pyramiding PRRs for a more efficient and durable resistance. I think it is always important to keep in mind the field aspects and long term goals of our work in plant pathology so it was fascinating hearing it being discussed by such prominent researchers.
Jacquelyne Poon, University of Cambridge
The opening lecture was given by Professor Fred Ausubel, who gave an interesting overview of his career as a prominent scientist. To imitate the well described zigzag model of interactions between host plants and pathogens, he described his career as a zigzag career. Throughout the course of his career, Professor Ausubel touched upon various critical topics in biological sciences that were not limited to plant sciences, albeit he began his research in this area. His talk was rather inspiring for young, emerging scientists, who yet have to commit to a specific research topic. Instead, he encouraged young scientists to explore various topics and to not be afraid to revisit previously explored topics.
Besides these plenary talks, concurrent sessions gave attendees the chance to hear about top notch findings in the same research field and also other diverse research areas. Many of these talks were very fascinating and covered too many topics to be covered in this meeting report. Just to name a few, there have been rapid developments in pathogen effector biology, the modulation of hormone signalling pathways, and vesicular trafficking of membrane-localised immune receptors. Amongst the many striking talks, I would like to highlight a couple that I found interesting and refreshing. These included but are not limited to the identification of immune receptors using a MAMP-based receptor capture approach by Dr Patrick Boyle and the intercellular movement of turnip mosaic virus replication complexes by Dr Jean- Francois Laliberte
I had a chance to present my findings at the International Congress and was given the opportunity to discuss some ideas with other scientists from across the globe. These ideas would help shape my scientific thoughts as I continue my doctoral studies. Indeed, the opportunity to attend this International Congress was quite rewarding as a young, emerging scientist.
Louise Gamble, The James Hutton Institute
There were many diverse and outstanding talks throughout the conference, many of which were beneficial and of interest to my work. In addition the conference also provided a great opportunity to gain insight into other areas outside of my PhD project. I was interested to learn about new EU directives that will promote the progression of biocontrol agents to full scale applications. The talk highlighted some of the biologicals being used and how the area is developing and discussed whether we are technically and scientifically ready for them to play a larger role in agricultural systems. Another fascinating talk based on Albugo sp. – a genus of oomycete pathogens causing white rust disease, suggested that this pathogen infection promoted the growth of prokaryotic endophytes and questioned the enrichment of species such as Pseudomonas during colonisation of the apoplast. It was proposed that Albugo sp. specifically enrich for bacteria containing less cell wall degrading enzymes, influencing microbe-microbe interactions and ultimately, determining the plant microbiome.
There was three poster sessions throughout the conference which offered an opportunity to discuss my research and also to gain insights into what is being researched in phytopathology across the globe. It provided a good atmosphere to network and interact with other students and world-leading scientists. I presented a poster of my research on identification and characterisation of Avr genes in Rhynchopsorium commune. R. commune is an apoplastic fungal pathogen and little is known about the resistant mechanisms against this fungus. One particular poster which caught my attention was ‘Effector triggered defence against apoplastic fungal pathogens’ which proposes a new concept of plant response to invading apoplastic pathogens. I was introduced to a paper which had just been published on this work in Cell Press and highlighted some important points which I am incorporating into my research.
Lucy McCann, The Sainsbury Laboratory
Within my studies I have a particular interest in tomato-fungal pathogen interactions. During the conference we heard from Ioannis Stergiopoulos on the similarities of the structure of Cladosporium fulvum‘s Avr4 effector to other carbohydrate binding modules (CBM) including CBM14. Avr4 is present in multiple fungal species independent of their lifestyle, and conservation of structure and not amino acid sequence enables its conserved chitin binding function. In contrast, the Ave1 effector from Verticillium dahliae interacts with plant chitinases. Bart Thomma demonstrated that the Ave1 effector sequence resides within the pathogen’s unstable genomic region, with its sequence lost multiple times throughout evolution.
The cloning and characterisation of resistance genes to grass pathogens is of specific importance in the current climate, whereby wheat, barley and rice pathogens cause significant annual loss of yield. Patrick Schweizer’s group demonstrated that bombardment of select BACs carrying Receptor-like kinase (RLKs) from barley, up-regulated during barley powdery mildew infection, in to wheat enhanced resistance to wheat powdery mildew. Furthermore, Beat Keller’s group demonstrated that the durable wheat Lr34 gene, encoding an ABC transporter, increased resistance in rice to rice blast. However, Lr34 causes leaf tip necrosis, significantly reducing yield. To overcome this, they have selected a transformant, which has late onset of Lr34 expression, enabling delayed leaf tip necrosis. Such plants have yet to be tested for resistance to rice blast.
Within the field of plant-microbe interactions once resistance proteins are activated little is known about the signalling pathways and consequent transcriptional changes. Frank Takken shed some light on this with a stimulating talk regarding the tomato CC-NBLRR I2, which recognises the Avr2 effector of Fusarium oxysporum. They demonstrated that the NBARC domain of I2 binds double stranded DNA. Such binding was enhanced in the ATP bound state and decreased in the ADP bound state, with DNA binding stimulating ATPase activity. Similar binding was observed for R1 of Rice and Rx of potato. Furthermore, binding of the full length Rx to DNA only occurred in the presence of its cognate Avr (the Potato Virus X coat protein), and causes local strand separation. Such work provided potential insight into a very short signalling pathway from cytosolic resistance gene activation to altered gene regulation.
Georgia Mitrousia, University of Hertfordshire
Attending an important international conference such as MPMI in my home country has been a great experience. It was a very enjoyable conference for many reasons. The conference was partially organised by members of my previous lab in the Agricultural University of Athens. I have to admit that I really enjoyed introducing Syrtaki and other traditional Greek dances to the participants during the gala dinner. It was also great for me to introduce delegates to Greek food and to explore a little bit of the beautiful island of Rhodes with them.
I was particularly interested in the presentations on plant immunity and apoplastic defences. Presentations on programmed cell death and signalling were also very enlightening. It was exciting to be exposed to the latest developments in research on so many important plant pathogens. Meeting the people who wrote important publications in the field was very fascinating. Another interactive experience was manning the BSPP stand during coffee breaks. This gave me the chance to introduce the society to delegates from all around the world and to talk about the benefits of being a member.
The poster sessions were a very interesting experience. There were so many posters being presented during each of the sessions and it was great to see enthusiastic researchers communicating their results. I presented two posters that gave me the chance to talk about my recent research findings as well as to discuss a recently published Opinion article about Effector Triggered Defence in Trends in Plant Science.
Graham Motion, James Hutton Institute
My research as a PhD student is focused on Phytophthora capsici effector biology, with my project specifically aiming to use computational predictions to identify candidate DNA binding effectors to be validated in the lab. I was therefore particularly interested by sessions focusing on effector biology and large scale (OMICS) approaches. From the offset of the first concurrent sessions I was already finding interesting topics being covered. In the Large Scale ‘omics’ Approaches session Michael Udvardi discussed functional genomics of transcription factors that were involved in nodule development and symbiotic nitrogen fixation in Medicago truncatula. Through RNA-seq experiments they identified a set of genes required for nodule vascular bundle development. One of the particularly interesting effector talks was given by Lennart Wirthmueller from the Sainsbury Laboratory, who presented findings on the Hyaloperonospora arabidopsidis effector HaRxL106. He showed that this effector suppresses immunity through interaction with RADICAL INDUCED CELL DEATH1 (RCD1) from Arabidopsis.
Another highlight of the conference were the talks by Peter Palukaitis and Donato Gallitelli. Their talks were focused on the use of plant viruses to infect and silence genes in filamentous fungi and oomycetes. It has already been shown that using tobacco mosaic virus (TMV), the filamentous fungi Colletotrichum acutatum could be infected and caused to express a foreign gene, in this case GFP. Peter Palukaitis showed that using this same system Phytophthora capsici could be infected, with no detrimental effects to P. capsici growth. They were exploring use of this system to knockdown P. capsici endogenes, with results showing that targeting the autophagocytosis gene Atg3 caused a reduction in P. capsici growth. Donato Gallitelli’s presentation showed that they were working up a pathway for TMV movement and replication in infected C. acutatum cells. He also showed results of other plant viruses including Cucumber mosaic virus (CMV), Artichoke mottled crinkle virus (AMCV) and Potato virus X (PVX), being able to infect C. acutatum. Overall, these results suggested a new potential use of plant movement deficient viruses as tool for studying functional genomics of filamentous fungi, or possibly even as a means of biocontrol for these plant pathogens e.g. P. capsici.
Stefan Engelhardt, University of Dundee
Despite the fact that Greece’s agriculture is not a thriving economic sector due to the lack of many natural resources, it is still a major EU producer of cotton and tobacco, and its olives are the country’s most renowned export crop. But also the Greek agriculture faces a variety of plant pathogenic threats, e. g. the Verticillium wilt of olives. So Greece in general and Rhodes in particular was a fantastic choice of being the host for this meeting.
Endosomal trafficking clearly emerged as one upcoming topic of general interest in plant-microbe interaction research, not only because it’s important for my own work. Silke Robatzek gave a fascinating insight into endosomal transport of cell surface PAMP receptors like FLS2, EFR and PEPR1/2. Additionally, also autophagy becomes more and more a part of research that is worth having a look at. Talks by Mark Banfield and Tolga Bozkurt introduced the Phytophthora infestans effector protein PexRD54 which activates autophagy by binding and stabilising host ATG8 via its C terminus. Dingzhong Tang presented evidence that the exocyst component Exo70B1 contributes to autophagy related membrane traffic and is monitored by the TIR-NBS-LRR resistance protein TN2.
Other talks which I followed with great interest included Natalia Requena’s story about the influence of arbascular mycorrhiza fungal extract on the hormonal balance, Bostian Kobe’s protein structure analysis of the flax rust effectors AvrL367, AvrM and AvrP, and prokaryotic communities presented by Eric Kemen, where he showed that Pseudomonas are highly abundant endophytes in Albugo infections, indicating that Albugo significantly reshapes the host microbial community.
For my own work which I presented as a poster, “Chasing the candidate virulence targets of the effector protein Avr3a from the plant pathogenic oomycete Phytophthora infestans“, I got some very helpful discussions and valuable input. All in all this meeting was a fantastic and memorable experience, especially because immediately before the MPMI Conference I also attended the OMGN (Oomycete Molecular Genetics Network) Meeting in Norwich, so these 2 weeks have been fully packed with loads of brilliant scientific talks and discussions.
Susan Breen, The Australian National University
My research focuses on the effector proteins Tox1 and Tox3 from Stagonospora nodorum so Tim Friesen’s presentation on ‘The S. nodorum necrotrophic effector SnTox1 elicits recognition in wheat and then protects from the resulting host defence response’ was of great interest to me. He presented data showing that this effector stays on the surface of host cells and that its corresponding susceptibility gene, Snn1 which is required to induce cell death, is a wall associated kinase. Richard Oliver also gave a talk on S. nodorum and Pyrenophora tritici repentis, both fungi contain the effector protein ToxA. Richard discussed how breeders in Australia are using ToxA as a screening tool to test >100,000 wheat lines for resistance against P. tritici repentis. I thought Richard’s talk was interesting as it showed how fundamental research can be taken and applied to the field to identify resistant wheat lines to increase yield and food security.
Another talk which I found interesting was by Caitilyn Allen entitled Bacterial extracellular DNase: A novel virulence factor. She presented data showing that root boarder cells release extracellular DNA which forms NET-like structures which protect the roots and can trap bacterial cells within it. In response to these NET-like structures the bacteria secrete DNAses via the type two secretion system which degrade these structures and therefore act as a virulence factor.
Lieselotte De Bruyne talked about her PhD work entitled ‘Ophiobolin A is involved, but is not essential to Brown Spot Disease in Rice’. The Ophiobolin A synthase gene, CmOS, was knocked out in Cochliobolus myabeanas which resulted in no Ophiobolin A production. These knock out strains had significant reduction in lesion type and size. She also showed that for C. myabeanas, Ophiobolin A is linked to virulence during the first stage of infection which is a short biotrophic phase before the fungus turns necrotrophic.
Mark Derbyshire, Rothamsted Research
The main focus of my PhD research is fungal metabolism, and in particular the role of secondary metabolites in plant infection. Two concurrent sessions at MPMI entitled ‘Toxins’ and ‘Secondary metabolism’ catered to my interests very well as they covered the varying roles of secondary metabolism in numerous plant pathosystems including several plant-fungus interactions.
A particularly interesting plenary lecture entitled ‘Evolution of Fungal Chemodiversity’ was given by Antonis Rokas. The main focus of research in the Rokas lab is the evolution of the eukaryotic genome, which they investigate using both computational and experimental approaches. The talk given at MPMI was on a large scale computational analysis of secondary metabolite-producing genes in fungal genomes. Using data already available on EC50 values (a measure of toxicity) of fungal secondary metabolites and the numerous fungal genomes that have been sequenced, Prof Rokas and colleagues were able to show that genes encoding enzymes responsible for successive steps in the biosynthesis of secondary metabolites were more likely to be grouped together if the intermediate compounds produced by their cognate enzymes were toxic. Based on this finding it was hypothesised that toxicity of intermediate compounds is a major evolutionary force driving the clustering of secondary metabolite genes.
I would highly recommend the MPMI conference to anybody with an interest in molecular plant pathology and the next one will be held in the fabulous city of Portland, Oregon in 2016!
Yan Ma, The Sainsbury Laboratory
Plants have evolved resistance (R) proteins that recognize specific pathogen effectors to trigger immunity. In many occasions, R proteins (NB-LRR proteins) function together to mediate disease resistance. Functional mechanisms of the ‘paired’ R proteins are drawing rising interest in the field. In this meeting, talks on ‘paired’ R proteins are particularly relevant for my PhD project and very inspiring for me. Simon Williams and Jonathan Jones focused on different aspects to address the question of how the paired R proteins RPS4 and RRS1 from Arabidopsis function together to provide resistance to distinct pathogens. The former linked structural and functional studies, showing the first co-crystallization of the TIR domains from RPS4 and RRS1, and revealed the distinct role of TIR/TIR hetero- and homo-dimerization in receptor complex formation and defense signalling. The latter focused more on the recognition mechanism of this NB-LRR pair in which one member (RRS1) carries an additional protein domain (WRKY domain) enabling perception of pathogen effectors (AvrRps4 and PopP2) that target the WRKY domain. Laurent Deslandes independently showed evidence that Ralstonia solanacearum effector PopP2 acetylates RRS1 WRKY domain and also targets host WRKY proteins implicated in plant defense. These talks revealed an interesting phenomenon that one member of the paired NB-LRR proteins can adopt domains that are ‘decoys’ of effector targets for direct effector perception. Similarly, RGA4/RGA5 from rice also perceive effectors via an integrated RATX1 domain of RGA5 (Thomas Kroj). For less specific ‘pairs’, Chih-Hang Wu proposed a signalling hub model for NB-LRR protein NRB1, which is required for a subset of NB-LRRs (Rpi -blb2, R1 and Mi). Such ‘hub’ or ‘helper’ R proteins (NRB1, ADR1) may function differently compared to the specific pairs like RRS1/RPS4 or RGA4/RGA5.
How can the study of plant microbe interactions apply to translational research? In this meeting, the outlook of translational research was highlighted in many talks. To name a few prospects:cross-species engineering PRRs to provide a broader range of resistance; identifying elements that determine host range in an attempt to transform host to nonhost; engineering R proteins with novel resistance function with integrated additional domains. Exploring the practicalities of these ideas is an exciting goal for the future.
Claire Stoker, University of Warwick
Speakers within the hormone session included Corna Pieterse, whose work I find fascinating, after giving a general overview of hormonal cross talk, Pieterse went into greater detail on the interactions between jasmonic acid and salicylic acid. One finding I was very interested by was the revelation that the GCC-box motif, which binds ERFs, can be either repressed or activated by salicylic acid or jasmonic acid, respectively.
One talk that really stood out to me was Hailing Jin’s talk on the involvement of small RNAs (sRNAs) in fungal attacks. Previously it has been shown sRNAs regulate defence responses against pathogens and induce gene silencing by binding to AGO proteins and directing the RNA-induced silencing complex to specific genes. Jin’s group showed the fungus, Botrytis cinerea, secretes small RNAs (Bc – sRNAs) capable of suppressing host genes during infection. This was then confirmed as the group observed binding of the small RNAs to the host AGO proteins during ChIPseq and also B. cinerea lacking these small RNAs had decreased pathogenicity.
The conference closed on the Thursday evening after a wonderful set of plenary talks. The closing ceremony was then followed by the conference dinner held in a large beautiful room with a central pool, entertainment at the conference dinner was provided in the form of traditional Greek dancing! This was a very fun way to network and get to know the eminent scientists in my research area.
Laurence Bindschedler, Royal Holloway University of London
My suitcase was full of scientific take home messages. It started high with the opening lecture from Fred Ausubel, wrapping up science and anecdotes, from an impressing career. I can’t believe that he is really retiring, being still so active at the forefront of research. First we are thankful to Fred Ausubel for establishing Arabidopsis and C. elegans as model systems, as a start, then using Pseudomonas, as the model pathogen, and then many more systems, including Pseudomonas pathogenic to humans. No need to say that his legacy to plant pathology is colossal, including the cloning the RPS2 Arabidopsis R gene to investigate their mode of action or elucidating the biosynthetic pathway of salicylic acid.
There was also plenty of talks on PAMPs percept ion, and the molecular understanding of PTI, in particular in the Arabidopsis-Pseumomonas pathosystem, and this was incontestably dominated by the group of C. Zypfel. Once again this was accompanied by talks on effectors affecting PTI as well as ETI. I was particularly interested by the talk of G. Felix who clearly explained the concept that you first needs to discover the PAMPs to find the PAMPs recognition receptors (PRRs), and by studying motifs on the PRRs, how it is possible to understand the interaction with the PAMPs. I liked his long term vision that by understanding how the proteinprotein interactions works between the PAMPs and the PRRs, it will be possible to design new PRRs to improve the plant perception of PAMPs and there downstream signalling pathways for improved resistance. I believe this to be a clever strategy, as pathogens might have more difficulty to overcome an efficient multiple PTI to a specific ETI, relying on a single gene product on the plant and on the pathogen side.
Symbionts were also represented in excellent talks on symbionts-plant interactions. N. Requena investigated the mechanisms on how Arbuscular Mycorrizal Fungi (AMF) reorganise the host plasma membrane without triggering the host defence response. This is inhibited via stringolactone. GRAS transcription factors (TF) are expressed in host colonised cells, then affecting the Giberellin (GA) and auxin hormones metabolism. And DELLA protein, which inhibit GA pathway is required for AMF establishment. A series of (putative) effectors have been decribed: several SP7 and SP31 proteins, 7 NLS effectors, and 5 putative Crinkler effectors (CRNs), are required for AMF colonisation and symbiosis but surprisingly, CRN3 induces cell death in Nicotiana benthiamana. I was particularly impressed by the work of Maria Harrison, to describe the plant perception of Arbuscular Mycorrizal Fungi (AMF), describing the role of GRAS-TF required for AMF invasion.
Richard Cooper, University of Bath
The meeting sections were well thought through, often breaking the traditional format, and overall it provided much to digest and enjoy. It was good to catch up with the local organizer Eris Tjamos and family as we date back to PhDs at Imperial College in the 70s. I also approve of the venue. It was time to see the Greek islands again. My interests are broad so I will only offer a few selected personal highlights. Seeking acceptable alternatives to chemical control of disease is increasingly clear at least in a European context, and M. Lorito reviewed the contribution of and prospects for biocontrol. Also, alternatives to conventional breeding with R genes came through loud and clear with finding, transferring and pyramiding PRRs and NLRs rather than relying on one. For example in describing “effector -driven breeding”, V. Vleeshouwers, with potato late blight as her target, described the widespread effector recognition in diverse Solanum spp. ELR from wild potato S. microdontum mediated extracellular recognition of elicitin domain, a molecular pattern conserved in Phytophthora spp, including four from P. infestans. Wild Solanum recognize SCR74 a highly polymorphic apoplastic effector in P. infestans undergoing diversifying selection. Receptor identification is ongoing.
How to achieve durable resistance in the face of the staggering range and combinations of almost 200 effectors in genomes of Bremia lactucae populations (according to R. Michelmore), is another matter. K. Posthuma represented the horticultural industry and described the use of gene KO, silencing and EMS mutagenesis against the serious problem downy and powdery mildews. Their experience showed that R genes fail repeatedly in the face of new races. Non host resistance (NHR) has been a black box for so long but associated expressed genes are being identified and can be up-regulated. Reduced infection of soybean rust has been obtained in this way described by C. Langenbach.
I presented a paper in the session on diagnostics, which is not my usual habitat . The paper described development of a specific DNA-based detection system for Fusarium oxysporum f. sp. elaeidis, cause of the devastating vascular wilt of oil palm in Africa. I guess the talk was invited because it is a good example of application of in-depth understanding of plant-pathogen interactions. Thus we found a unique, putative virulence effector based on the f. sp. lycopersici genome and its SIX (secreted in xylem) effectors. The PCR test will be used for example at quarantine to prevent interregional and -continental disease spread on exported African seed and pollen used for breeding purposes, especially in SE Asia and S and C America.
