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The XIV International Congress of Virology (ICV) was held in the beautiful city of Istanbul, from 10-15 August 2008. Istanbul is the only city in the world built on two continents, Europe and Asia, and was an imperial capital for 1600 years. For one week about 1000 virologists from around the world came together to discuss recent advances in basic and applied virology covering all current aspects of research on human, animal, plant viruses and bacteriophages. As a meeting of such magnitude and diversity, the XIV ICV afforded participants the opportunity not only to discuss with others their own field of interest, but also to broaden their vision of the whole field of Virology. Given the generality in structure and functions of all viruses regardless of their hosts, the exchange of knowledge and ideas between animal and plant virologists enriches both sides with new tools and approaches.
The five conference days were split into five plenary sessions, 68 (!) parallel symposia and poster sessions. With these many competing talks, one felt the inevitable frustration of having to decide which of several equally interesting talks to attend. Among the traditional plant virology highlights were the sessions on virus replication and translation, virus suppression of RNA silencing, resistance mechanisms, virus movement and plant virus-vector interactions as well as specialized symposia on particular virus groups such as closteroviruses, plant DNA viruses, viroids and satellite viruses. The short format of this report does not allow me to mention all the interesting and important talks, and hence I will focus on my own scientific preferences.
RNA silencing is a fast developing area of molecular biology which plays a very important role in our understanding of the key antiviral defence mechanisms in plants. Viruses can induce RNA silencing, which subsequently targets the viral genome. In return, viruses have employed protein-mediated suppression as a common means to counter silencing defence during infection. J. Burgyan (Agricultural Biotechnology Center) and V. Vance (University of South Carolina) presented excellent overviews of the molecular mechanisms and side effects of viral RNA silencing suppressors and the role of host factors in viral suppression of silencing. Another type of antiviral resistance mechanisms in plants is innate immunity which is controlled by plant resistance genes and characterized by the hypersensitive response (HR). S. Dinesh Kumar (Yale University) focused on the tobacco resistance gene N that encodes a member of the so called TIR-NBS-LRR class of proteins. N gene-containing plants specifically recognize the 50 kDa helicase domain of tobacco mosaic virus and trigger signal transduction cascades leading to the induction of HR, restriction of virus spread and onset of systemic acquired resistance. C.
Caranta (INRA) presented several lines of evidence showing that translation initiation factor eIF4E plays an important role in resistance to potyviruses. The virulence determinant toward this recessive resistance is the potyvirus-encoded VPg protein and failure of eIF4E alleles to bind VPg correlates with resistance. Anne Simon (University of Maryland) who chaired a symposium on virus replication and translation presented a new concept of the switch between translation and replication in a plus-strand RNA virus. She demonstrated that a conformational re-arrangement in the RNA that occurs upon binding by RNA replicase, precludes 60S ribosome interaction with the RNA template leading to the switch from translation to replication in turnip crinkle virus.
The next step of plant virus infection is systemic spread or movement of the virus over the infected plant. A very interesting talk on how potato leafroll virus (PLRV) invades infected plants was presented by P. Palukaitis (Scottish Crop Research Institute). Usually this virus is restricted to the phloem and cannot be transmitted mechanically. It was generally accepted that the virus lacks either a cell-to-cell movement protein or a plant defence suppressing protein. However, Palukaitis presented clear evidence that deletion of the translational read through portion (or its C-terminal part) of the major coat protein allows the virus to invade mesophyll cells and to be mechanically transmissible, suggesting that virus directed phloem limitation of PLRV and other poleroviruses may have evolved to facilitate its (their) transmission by phloem-feeding aphids. My talk also addressed mechanisms of phloem associated systemic spread of viruses and focused on the involvement of subnuclear compartments, the nucleolus and Cajal bodies, in systemic infection of umbraviruses. After a plant has been infected and virus progeny has been generated, a virus spreads from plant to plant often using vectors. On the epidemiological level, this process is likely related to a number of phenomena affecting virus populations and their evolution. S. Blanc (INRA) described mechanisms of noncirculative transmission of plant viruses by aphid vectors which represent the predominant strategy for virus-vector interaction. In particular, he characterized aphid receptors involved in transmission of cauliflower mosaic virus.
Traditionally the central focus of plant virus research has concerned their prominent role as pathogens. However, recently plant viruses have become used as tools in newly emerging fields of biotechnology (expression vectors for production of pharmaceuticals and industrial proteins in bio-farming), and even nanotechnology (virus particles as templates for materials production, etc.). These novel and intriguing issues were the focus of the session organised by S. Lommel (North Carolina State University). In conclusion I would like to thank BSPP for the travel grant giving me the opportunity to attend the XIV ICV. The next International Congress of Virology will be held in Sapporo Japan in September 2011.
Michael Taliansky, Scottish Crop Research Institute
Thanks to the BSPP for providing a Travel Grant which allowed me to attend the XIVth International Congress of Virology in Istanbul, Turkey on the 10-15th August 2008. The Congress covered both animal and plant viruses. Plenary and concurrent sessions included topics such as virus suppression of RNA silencing, virusvector interactions, and virus movement in plants. Strategies for replication and translation and the secondary structure of viral RNAs featured heavily in the plant virus sessions. One of these talks was presented by Andrew Firth (University College, Cork, Ireland) whose group identified a new short overlapping gene in Turnip mosaic virus termed ‘pretty interesting potyviral ORF’ (PIPO), which is essential for infection in Nicotiana benthamiana. This gene is embedded within the P3 cistron of the polyprotein, but is translated in the +2 reading frame. Bioinformatic analyses suggest PIPO is present in genomes of all other members of Potyviridae family. Andrew Firth’s group is now trying to identify the precise biological role of PIPO, and to identify potential overlapping ORFs in genomes of other viruses using a bioinformatics approach. The group has already identified a new overlapping ORF in the genome of waikaviruses in the family Sequiviridae.
I was given the opportunity to orally present my PhD work, which resulted in discovery of a novel type of resistance to furoviruses in barley and its importance as a potentially novel furovirus-resistance source for hexaploid wheat breeders, in the ‘Plant virus: resistance mechanisms’ session. The pathosystem I have presented was more applied than the others described at the congress, and provoked interesting discussions especially with other scientists working on other agronomically important viruses. In the same session, Savithramma Dinesh- Kumar revealed the subcellular mechanisms of resistance to Tobacco mosaic virus (TMV) in Nicotiana benthamiana. Using the microscopic technique FLIP – FRAP (Fluorescence Loss in Photobleaching – Fluorescence Recovery after Photobleaching), he showed movies of the N receptorinteracting protein 1 (NRIP1) moving from the chloroplast to the cytoplasm and nucleus, where it could interact with the N resistance gene product. He showed that NRIP1 was recruited by the TMV avirulence protein p50, and that recognition between NRIP1 and N only occurred when NRIP1 was bound to p50. Carole Caranta (INRA, France), gave an overview of her findings on the co-evolution arm race between plant translation initiation factors (eIFs) and viruses in different pathosystems. Data was also presented in the poster sessions on the structural properties of eIFs and viral proteins known to interact with them, such as the potyviral genome-linked protein (VPg). This was of particular interest because our group is aiming to identify novel natural eIF variants in barley germplasm providing broad-spectrum resistance to bymoviruses, which belong to the Potyviridae family.
The plant virus-vector interaction session was chaired by Stephane Blanc (INRA, France), who described a previously unidentified anatomical zone located at the extreme distal tip of the of the aphid maxillary stylet that specifically interacted with the P2 protein of Cauliflower mosaic virus (CaMV). This interaction is essential for successful virus transmission. He then provided evidence that the specific receptor for CaMV in the aphid vector was a non-glycosylated protein deeply embedded in the chitin matrix. The search is now on to see if other aphid transmitted viruses utilise similar receptors. In the session on virus movement in plants Peter Palukaitis (SCRI, Dundee, Scotland) presented a fascinating story about another aphid transmitted virus, Potato leafroll virus (PLRV), which is normally limited to the phloem. He showed that when parts of the PLRV coat protein read-through domain were mutated, systemic accumulation of the mutant PLRV was delayed and in the first few weeks after inoculation the virus also moved out of the phloem into the surrounding mesophyll cells. Interestingly, however, during the later stages of infection the mutant virus reverted back to the wildtype, phloem-limited version. The hypothesis proposed to explain this phenomenon was that phloem limitation increases the efficiency of virus systemic movement and acquisition by the phloem-feeding aphid vector.
Steven Lommel (North Carolina State University, USA) provided a fascinating overview on how plant viruses can be exploited in nanotechnology. His research focussed on using Red clover mosaic virus (RCMV) particles for drug delivery. By altering cation strength, the RCMV virion can be opened, the drug or other ‘cargo’ added into the empty cavity, and then closed up again. The cargo-carrying virions can be targeted to specific animal cell types by attaching receptor peptides onto the outer surface of virus particles. He showed that when delivered via RCMV, the drug had 10 fold more toxicity in cancerous cells than when the free drug was injected and that the virus itself caused no acute toxicity to the mouse. Shri-Dong Yeh (National Chung Hsing University, Taiwan) used the genome of Turnip mosaic virus to express the dust mite allergen, Der 5, in the leaves of edible crops for use in immunotherapy. His presentation attracted some concerns from the audience regarding biosafety, considering the infectious nature of the recombinant virus. TuMV is mechanically as well as aphid transmissible, and thus manipulation of the virus to attenuate infectivity or aphid transmissibility is essential before release to the public.
I was slightly concerned about safety in the Istanbul city after the recent bombings in the news. However, security at the Congress was tight, with metal detectors and a number of machine-gun toting soldiers to pass before entrance to the building. In my opinion, however, the confiscation of my peach and sandwich at the door was a step too far. During the congress I met up with Nazli Kutluk Dide Yilmaz, a Turkish scientist who worked previously in our lab as an EMBO fellow. I stayed for an extended break for some sightseeing after the congress, and she and her family (who live over the Asian side of the Bosphorus) showed me the delights of the city. Istanbul was a wonderful vibrant place to visit, and much fun was had cruising up the Bosphorus, visiting the mosques, and sampling the food, spices, teas and the local tipple, ‘raki’, which turned out to be slightly more potent than expected. Attendance at this Congress was a great opportunity to meet with eminent animal and plant virologists, to present my work to an international audience and to visit Turkey for the first time.
Rebecca Lyons, Rothamsted Research