BSPP News Summer 2002 - Online EditionThe Newsletter of the British Society for Plant Pathology
Number 42, Summer 2002
Interactions in the Microbial
World: 9th International Symposium on Microbial Ecology
Amsterdam, The Netherlands : 26 - 31 August 2001
This was a very big meeting indeed! As the title suggests, it covered extremely diverse areas of microbiology. The Introductory lecture was given by Rita Colwell, setting the scene for the treats in store. Under the catholic banner of "microbial ecology" the symposium programme contained session topics on Biodiversity, Strategies for adaptation and survival, Bioremediation, Interactions between bacteria and fungi, Ecotoxicology, Microbial ecology of the gastrointestinal tract, Active but not culturable micro-organisms, Interactions in gradients and biofilms, Experimental evolution, Growth in extreme environments and Reaction to stress and perception to the environment. Perhaps more importantly from the point of view of the BSPP interests, there were full sessions on Synergistic interactions, Control of plant pathogens and pests, Predation and parasitism, Interaction of bacteria with their biotic and abiotic environment, Interactions between plants and micro-organsims, Microbial ecology in agricultural production and the food industry, and (the main reason for my attendance) Cell-to-cell communication. Obviously there was significant overlap in some of these parallel sessions and so it was simply impossible to get to everything that looked interesting – total information overload! Furthermore, main talks were supplemented by multiple round table sessions and a massive spectrum of posters relating to the main sessions and more general topics in microbial ecology and methodology.
There were plenary sessions too, for example Lugtenberg on plant-microbe interactions in the rhizosphere, Timmis on the microbial community as a biological catalyst and deLong on functional genomics in microbial ecology. There were also talks and posters on insect pathogens, biocontrol via antibiotics and toxins, antibiotic resistance gene dissemination (from hospital to soil and water), viral and protozoal control of bacterial populations, and environmental cue sensing. There were presentations on metagenomics, biogeochemical cycling, costs and benefits of pathogenicity, chemical signalling in plant-beneficial rhizobacteria, microbial gene transfer in soils, endophytic bacteria in potatoes, chitinases from marine bacteria, use of microarrays to investigate mixed microbial communities, chemotaxis and root colonisation, proteomics in the analysis of potato scab, endosymbiosis and endosymbionts, adaptation of plant pathogenic bacteria to low temperatures – and the list goes on and on.
Given the sheer diversity of things on offer, there could be little surprise that there was great variation in quality of the presentations and content. There also seemed to be considerable redundancy, with lots of groups investigating related issues, using very similar techniques. As I am not an ecologist, I went to the meeting with the intention of taking in the broadest possible sweep of presentations. However, the sheer volume on offer meant that I had no option but to be semi-selective about what I went to see, or hear about. [The geography of the buildings didn't always help in this regard, as some of the sessions were some considerable distance apart and delegates were commonly seen running between sessions!]
Apart from the complete sessions on cell-cell communication and some of the sessions on plant pathology-related themes, I was able to hear or read about interesting work on bacteriophage-host evolution, resuscitation methods for VNC-type pathogens, bioluminescent fungi, regulation of cyanobacterial toxin production, uses of variant GFPs in transient and single cell gene expression studies and fluorescent pseudomonad diversity in the rhizosphere. Further presentations included secondary metabolites from marine organisms, co-regulation of cholera toxin and pilus genes, peptide pheromones in gut bacteria, plasmids in insect pathogenic Serratia spp., surface sensing in microbes, plant-inducible genes, lipopeptides and phloroglucinols in biocontrol, capturing large gene clusters by metagenomics, pH stress sensing, bdellovibrios, biosurfactants, Type III protein secretion systems in non-pathogens, chemotaxis, squid-Vibrio symbiosis and, finally, the discovery of a fascinating, novel (perhaps unique) algal virus.
By "skimming" through as many sessions and posters as I could, I got a general feel for the rich diversity of microbial ecology research. It would be impossible to summarise the details of such a panorama of microbiological topics in a short report. However, for someone with less than a comprehensive background in microbial ecology, this was a very illuminating meeting as it introduced me to a wide range of topics, sometimes very peripheral indeed to my main interests. This gave me useful ideas about research avenues that I would not have considered before this meeting.
I enjoyed the symposium and I thank the BSPP for their very generous award allowing me to get to the full meeting.
University of Cambridge
Salt Lake City, USA : 25 - 29 August 2001
Sitting in Aberystwyth in the mid-winter rain, my thoughts drifted to
memories of my visit to the Annual Meeting of the APS. The
meeting was held in Salt Lake City, the state capital of Utah, where it
didn't rain for the whole six days of my stay, the sun was out, and the
temperature was in the 30's centigrade.
The city lies in a high valley between two incredible mountain ranges, the Oquirrhs to the west and the Wasatch to the east. It is the religious centre of the Mormons (Latter Day Saints) and alcohol is banned. Apparently, it is illegal to be in possession of a beer keg in the state, and local bar-owners brew their own beers in huge silver-coloured casks. Some of these are very strange concoctions e.g. lager made with fresh chillies. Nearby is the Great Salt Lake. It is a remnant of a much larger freshwater lake, but following a fall in the water table this was left with no outlet and shrank as a result of evaporation leaving the Great Salt Lake Desert. The combination of evaporation with the inflow of surface water rich in minerals led the salt content of the lake to rise steadily.
The conference was held in the splendid Salt Palace Convention Center, where several scientific sessions ran simultaneously. Over the four days, the talks were very diverse in content with sessions including: What is a fungal species?, The biology of pathogens, The role of fungal extracellular matrix in host infection, Diseases of plants, Plant microbe interactions at the molecular and cellular level, and The importance of plant pathology in global trade.
I attended too many presentations to list, but a few highlights deserve mention. I particularly enjoyed the presentation by H. K. Ngugi from the University of Georgia, Athens who discussed mummy berry disease of blueberry flowers due to infection by Monilinia vaccinii-corymbosi. The conidia germinate on the stigmatic surface and invade the ovary through the stylar canal. The rate of conidial germ tube growth is greatest on newly opened flowers and decreases with flower age; pollination increases the rate of conidial germ tube growth; and stigmatic exudate strongly increased conidial germination in vitro. Much of my own work has investigated the directional emergence and growth of conidial germ tubes and fungal exudate release, so Ngugi's report was especially interesting.
During one of the poster sessions, I was fascinated to learn that ozone gas has been proposed as a potential alternative to methyl bromide to fumigate stored grain (Mendez et al., Purdue University, West Lafayette). Fumigation is required to control pests such as larval Indian meal moth, adult maize weevil and adult red flour beetle. I thought it was an attractive proposal as it simply breaks down to oxygen, leaving no residue behind and of course it can be used repeatedly with no detrimental effects. In addition, it can be generated relatively easily on site eliminating the need for storage and disposal of chemical containers.
For me, one of the main highlights of the meeting was listening to Harvey Hoch, Cornell University, New York report on the applications and opportunities for nanobiotechnology in cell biology. It is an emerging area of science and technology, and brings together collective efforts of biologists, engineers, physicists, and chemists. Nanobiotechnology is based on the ability to fabricate materials and pattern surface chemistry at small dimensions. Among the explorations being pursued are tools to detect and analyse small numbers of biologically relevant molecules, bioselective filtration devices for separating complex mixtures of molecules, and molecular motors to power micro-devices useful in cell biology.
On the Monday afternoon I presented an oral paper entitled 'Surface sensing and response in Blumeria graminis – micro-manipulation and geometric modelling'. It was the first time I had spoken at an international symposium and although I was very nervous, I felt greatly honoured and thoroughly enjoyed the challenge. I am very grateful to the BSPP for the travel award that enabled me to attend the meeting.
Institute of Grassland & Environmental Research
Spots, Blights and Scalds in Syria:
2nd International Barley Leaf Blight Workshop
ICARDA, Aleppo, Syria : 7 - 11 April 2002
"Rather you than me" was a comment I received when I said I was going to a Workshop in Syria in April, when things were getting somewhat volatile in the neighbouring areas of Palastine and Israel. However, we all received nothing but excellent hospitality; in fact, ICARDA set a standard which it is difficult to match. The people of Aleppo were similarly welcoming and made the whole trip very enjoyable.
The First International Barley Leaf Blight Workshop had been held nine years previously with no date set for a follow-up. Eventually a group of people at the International Barley Genetics Symposium in Adelade in November 2000 decided that a Scald workshop should take place. This grew into 'barley leaf blights' and the 'Second International Barley Leaf Blight Workshop' was conceived.
ICARDA is the International Center for Agricultural Research in the Dry Areas, serving in particular the CWANA (Central and Western Asia and North Africa) region. It is a well funded institute which clearly knows its mission. All of its research work is carried out in collaboration with the relevant groups worldwide, and its training role in arid region agriculture is obviously very effective. The facilities for these roles are of a high quality and it was great to see an organisation properly equipped and funded to carry its function. The later visits to the laboratories: Biotechnology and Genetic Resources, and the field visits: Pathology and Breeding, were similarly interesting and impressive.
The papers sessions were generally headed 'Disease Epidemiology', 'Disease Management', 'Resistance Breeding & Genetics', 'Ramularia' and 'Biotechnology & Barley Diseases', although there was overlap which made for good continuity. There were also four workshops: 'Update & status of spot blotch', ''Work on genetics of scald resistance', 'Ramularia', and 'Net blotch', the latter two running concurrently. The workshops all resulted in various collaborations forming, or agreements on standard methods, nomenclature or genetic material such as differential cultivars. The scald workshop, for example, continues as an 'International Barley Scald Working Group' with its own web site: www.crpmb.org/scald which I will look after (I never learn!).
It is difficult to write about any particular 'highlights' without going on for pages about each paper as there were so many valuable contributions. Perhaps it is best to highlight the whole day we devoted to 'Ramularia'. Ramularia collo-cygni, for those not in the barley world, is the causal agent (?) of a disease (?) which has enjoyed great prominence in the last few years. Why the "(?)"? We had first to establish whether the symptoms observed or recorded as 'Ramularia' were indeed caused by this pathogen, or were they forms of 'spot blotch', 'net blotch', 'spotting form of net blotch', 'physiological leaf spots', 'sun scorch', any combination of these or what. As someone who has never worked on this disease but thought I might have seen it, I ended up convinced that it is a real disease in its own right after all. Some excellent papers clarified its epidemiology, and why various other diseases or physiological and genetical factors have confused its diagnosis in the past. The following workshop session filled in many of the practical points and raised many questions which will facilitate future research. There is clearly still a need for a much greater understanding of this pathogen's epidemiology before it can be effectively controlled through either fungicides, agronomy or resistance.
Finally I want to express my thanks, firstly to ICARDA, especially Amor Yahyaoui the Chair of the Local Organising Committee, and his team. Whilst his team were brilliant, it was Amor who was the first to initiate the solution to any problem we came up with. We tried our best to test his patience but somehow he engineered an effective solution to every problem. We discovered the secret of his patience later: imported Danish beer at 10.5% alcohol (or was that barley wine?), even the Danes were impressed with that! Secondly to the International Organising Committee and its Chair, Andy Tekauz, who did an excellent job with the programme. Thirdly, to all the participants who did what they were supposed to do, i.e. participate in all the discussions. It was a very effective exchange of ideas and information of great relevance to the research we all do. And finally to BSPP of course for a contribution to my costs. Without this I would not have been able to attend what was probably the most useful meeting I have attended for several years - thanks.
Adrian C Newton,
Scottish Crop Research Institute
Cambridge : 12th April 2002
The 2002 Powdery Mildew meeting held in April at Trinity College Cambridge attracted a wide range of contributions from many of the UK and European research groups working on powdery mildews. Presentations were both highly informative and interesting, covering subjects such as fungicide resistance, pathogen virulence and transformation technology, as well as host and non-host defence responses.
During the first session on fungicide resistance, Alison Hall (Syngenta) outlined the current status of resistance in commercially important pathogens, including Blumeria graminis of wheat and barley, to the QoI class of fungicides alternatively known as 'Strobilurins'. Syngenta use a combination of field monitoring techniques, spore germination assays and allele-specific real-time PCR technology (ARMS-SCORPION™ assay) to detect the extent, and rate of spread of resistance in Europe. Resistance is associated with a single base pair mutation (G143A) in the mitochondrial Cytochrome b gene. Bart Fraaije (IACR, Rothamsted) described the use of a RT-PCR Taqman probe assay to study the dynamics of the stobilurin resistant allele in field populations of B.graminis f.sp. tritici (Bgt) The use of molecular techniques to monitor resistance in Chinese populations of Bgt to a different class of fungicides the triazoles, specifically triadimefon, was described by Xiayu Duan (Chinese Academy of Agricultural Sciences, Beijing). The evolution of cereal pathogens to overcome host resistance genes deployed in common varieties was reported by John Clarkson (NIAB, Cambridge). Perhaps of most interest is the recent evidence that field isolates of Bgh have evolved partial virulence to mlo. However, importantly, there had been no breakdown of mlo resistance in the field to date.
The second session of talks focused on the current status of research into the molecular and genetic characterisation of barley powdery mildew (Bgh). Groups in the UK and Denmark, represented by Chris Ridout (JIC, Norwich) and Solvieg Christiansen (Risø), have independently generated a genetic map for Bgh and are currently attempting to delimit avirulence gene loci closely linked to molecular markers. The use of transformation technology to test the function of putative avirulence genes has been hampered by the lack of a stable transformation system. The common problem, as explained by Sabine Eckert (Imperial College, London) is selection, using Bialaphos (BAR gene) or Benomyl as the selectable marker. Both gold particle bombardment and Agrobacterium-mediated transformation frequently yield false positives, i.e. transformants that cannot be confirmed by PCR or southern analysis. The possible use of a 'surrogate' non-biotrophic pathogen e.g. Magnaporthe grisea for transformation with Bgh avr genes was proposed. Ziguo Zhang (University of Oxford, UK) outlined how a 'Primer walking' technique has been used to identify a large number of Bgh genes involved fungal cell wall generation and turnover, plant cell wall penetration, and nutrient uptake. Transformation and gene silencing using the RNAi complex were used to further test gene function.
The focus of presentations in the afternoon session shifted to powdery mildew of Arabidopsis. Evolutionary and functional analysis of the RPW8 (Resistance to Powdery Mildew) locus in Arabidopsis, has been undertaken by researchers in John Turner's group (Kumrop Ratanasut & Piyavadee Charoenwattana) at the University of East Anglia, Norwich. Homologues of the RPW8 locus have been identified in important crop plants including Brassica rapa and B. oleracea, tobacco and tomato.
Factors determining non-host resistance are also being investigated using Arabidopsis, infected with barley powdery mildew. Arabidopsis mutants hampered in their penetration resistance to Bgh have been developed at Risø in Denmark (Hans Thordal-Christiansen) and at the Max Planck Institute in Germany (Volker Lipka). Two mutations, causing enhanced cell wall penetration (Pen1-1 and Pen1-2), have been identified, mapped and partially characterised.
The presentation given by Anna-Liisa Laine (University of Helsinki, Finland) on the spatial dynamics of host plant-fungus interactions in a fragmented landscape provided a refreshing diversion from molecular resesarch on powdery mildew. Anna-Liisa described her work on the temporal and spatial variation in susceptibility of Plantago lanceolata to infection by the powdery mildew pathogen Podosphaera (syn. Sphaerotheca) plantaginis, in the Aland islands of Finland. The practical applications of powdery mildew research was highlighted by Charles Lane (CSL, Sand Hutton), who described how recent technical advances in electron microscopy and molecular biology facilitate the accurate taxonomic classification of powdery mildews based upon characteristics of the anamorph. Charles gave the example of how this enables the efficient monitoring of new introductions of powdery mildew species e.g. powdery mildew of Poinsettia, into the UK. John Russell (HRI, East Malling / University of Kent, Canterbury) explained how the study of genetic diversity and host specificity in Ampelomyces quisqualis may improve the use of this powdery mildew hyperparasite as a biocontrol agent.
The final session concentrated on cellular host-defence responses and signalling pathways. Michael Lyngkjaer (Risø) outlined the novel approach of single-cell extraction to study how individual barley cells respond to mildew attack. The contents of the infected cell are removed by a capillary needle and used to make an uncloned single cell library, which can then be hybridised against known barley genes to identify any which are down-regulated or suppressed in response to pathogen haustoria formation etc in the cell. Peter Roberts (IGER, UK) then went on to describe the affect of silicon in induced (in)accessibility in oat epidermal cells. The rate and amount of silicon deposition is of vital importance in conferring host resistance to powdery mildew infection. However, double-inoculation experiments demonstrate that the presence or absence of silicon does not affect the percentage of haustoria or papillae formed by a challenger in previously induced cells.
The last two talks detailed components involved in host-defence signalling pathways. Ralph Panstruga (Max Planck, Germany) described how 7 Trans-Membrane helices of the Mlo protein function as receptors for signalling molecules independently of GPCR proteins, but regulated in-vitro by the cytoplasmic Ca2+ sensor calmodulin. The defence signalling complex involved in Mla determined resistance of barley to Bgh, specifically the interaction between the RAR1 and Sgt1 protein components of the complex, was explained by Ken Shirasu (Sainsbury Laboratory, Norwich).
The general consensus of all participants was that the 2002 Powdery Mildew meeting was highly successful. Grateful acknowledgements go to the meeting's organiser James Brown (JIC, Norwich) and to the meeting's sponsor, the British Society for Plant Pathology.
John Innes Centre