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Two important hallmarks of RNA silencing in plants are (1) its ability to self amplify by using a mechanism called transitivity and (2) its ability to spread locally and systemically through the entire plant. Crucial advances have been made in recent years in understanding the molecular mechanisms of these phenomena. We review here these recent ??ndings and we highlight the recently identi??ed endogenous small RNAs that use these advantageous properties to act either as patterning signals in important developmental programs or as a part of regulatory cascades.

To successfully infect plants viruses must counteract small RNA based host defense responses. During infection of Arabidopsis Cauliflower mosaic pararetrovirus (CaMV) is transcribed into pregenomic 35S and subgenomic 19S RNAs. The 35S RNA is both reverse transcribed and also used as an mRNA with highly structured 600 nt leader. We found that this leader region is transcribed into long sense and antisense RNAs and spawns a massive quantity of 21 22 and 24 nt viral small RNAs (vsRNAs) comparable to the entire complement of host encoded small interfering RNAs and microRNAs. Leader derived vsRNAs were detected bound to the Argonaute 1 (AGO1) effector protein unlike vsRNAs from other viral regions. Only negligible amounts of leader derived vsRNAs were bound to AGO4. Genetic evidence showed that all four Dicer like (DCL) proteins mediate vsRNA biogenesis whereas the RNA polymerases Pol IV Pol V RDR1 RDR2 and RDR6 are not required for this process. Surprisingly CaMV titers were not increased in dcl1/2/3/4 quadruple mutants that accumulate only residual amounts of vsRNAs. Ectopic expression of CaMV leader vsRNAs from an attenuated geminivirus led to increased accumulation of this chimeric virus. Thus massive production of leader derived vsRNAs does not restrict viral replication but may serve as a decoy diverting the silencing machinery from viral promoter and coding regions.

Many scientists if not all feel that their particular plant virus should appear in any list of the most important plant viruses. However to our knowledge no such list exists. The aim of this review was to survey all plant virologists with an association with Molecular Plant Pathology and ask them to nominate which plant viruses they would place in a ‘Top 10’ based on scientific/ economic importance.The survey generated more than 250 votes from the international community and allowed the generation of a Top 10 plant virus list for Molecular Plant Pathology.The Top 10 list includes in rank order (1) Tobacco mosaic virus (2) Tomato spotted wilt virus (3) Tomato yellow leaf curl virus (4) Cucumber mosaic virus (5) Potato virus Y (6) Cauliflower mosaic virus (7) African cassava mosaic virus (8) Plum pox virus (9) Brome mosaic virus and (10) Potato virus X with honourable mentions for viruses just missing out on the Top 10 including Citrus tristeza virus Barley yellow dwarf virus Potato leafroll virus and Tomato bushy stunt virus. This review article presents a short review on each virus of the Top 10 list and its importancewith the intent of initiating discussion and debate amongst the plant virology community as well as laying down a benchmark as it will be interesting to see in future years how perceptions change and which viruses enter and leave the Top 10.

A framework for comparative studies of binaurally resynthesized acoustical environments is presented. It consists of a software-controlled, automated head and torso simulator with multiple degrees of freedom, an integrated measurement device for the acquisition of binaural impulse responses in high spatial resolution, a head-tracked realtime convolution software capable to render multiple acoustic scenes at a time, and a user interface to conduct listening tests according to different test designs. Methods to optimize the measurement process are discussed, as well as different approaches to datareduction. Results of a perceptive evaluation of the system are shown, where acoustical reality and binaural resynthesis of an acoustic scene were confronted in direct A/B comparison. The framework permits, for the first time, to study the perception of a listener instantaneously relocated to different binaurally rendered acoustical scenes.

Le Banana streak virus ou BSV, responsable de la mosaïque en tirets des bananiers est la contrainte majeure de la filière banane du fait de la présence de séquences virales endogènes au génome bananier. Ces bananiers d'apparence saine, sous l'action d'un stress se révèlent infectés, exprimant le virus et la maladie. Une approche ARN interférant (ARNi) basée sur le blocage du promoteur BSV a été initiée afin de stopper toute possibilité de multiplication virale tant à partir du virus que des séquences endogènes. Ainsi une construction constituée d'une région de 332pb de la zone promoteur du BSV souche Obino l'Ewai (BSV-Ol) sens et antisens séparée par un intron a été obtenue. Elle a été mise sous le contrôle du promoteur du CaMV 35S et d'un signal PolyA permettant la restitution d'ARN double brins type "hairpin" aberrants. Cette construction a été ensuite bombardée sur des feuilles de bananier cavendish (AAA) agés de 10 jours ne possédant pas d'EPRV BSV et présentant une infection BSV-Ol. La diminution de la multiplication virale attendue a été suivie par PCR et IC-PCR semi quantitative sur la feuille bombardée et toute nouvelle feuille émise pendant 3 semaines. La technique de bombardement sur bananier a été adaptée en utilisant le gène rapporteur de la GFP. Les premiers résultats montrent une diminution significative de la multiplication virale dans un faible nombre de bananiers bombardés par PCR semi quantitative. Les autres analyses sont en cours de traitement. (Texte intégral)

Cauliflower mosaic virus (CaMV) open reading frame III (ORF III) codes for a virion-associated protein (Vap), which is one of two viral proteins essential for aphid transmission. However, unlike the aphid transmission factor encoded by CaMV ORF II, Vap is also essential for systemic infection, suggesting that it is a multifunctional protein. To elucidate the additional function or functions of Vap, we tested the replication of noninfectious ORF III-defective mutants in transfected turnip protoplasts. PCR and Western blot analyses revealed that CaMV replication had occurred with an efficiency similar to that of wild-type virus and without leading to reversions. Electron microscopic examination revealed that an ORF III frameshift mutant formed normally structured virions. These results demonstrate that Vap is dispensable for replication in single cells and is not essential for virion morphogenesis. Analysis of inoculated turnip leaves showed that the ORF III frameshift mutant does not cause any detectable local infection. These results are strongly indicative of a role for Vap in virus movement.