Structural Insights into Viral Determinants of Nematode Mediated Grapevine fanleaf virus Transmission

Many animal and plant viruses rely on vectors for their transmission from host to host. Grapevine fanleaf virus (GFLV), a picorna-like virus from plants, is transmitted specifically by the ectoparasitic nematode Xiphinema index. The icosahedral capsid of GFLV, which consists of 60 identical coat protein subunits (CP), carries the determinants of this specificity. Here, we provide novel insight into GFLV transmission by nematodes through a comparative structural and functional analysis of two GFLV variants. We isolated a mutant GFLV strain (GFLV-TD) poorly transmissible by nematodes, and showed that the transmission defect is due to a glycine to aspartate mutation at position 297 (Gly297Asp) in the CP. We next determined the crystal structures of the wild-type GFLV strain F13 at 3.0 Å and of GFLV-TD at 2.7 Å resolution. The Gly297Asp mutation mapped to an exposed loop at the outer surface of the capsid and did not affect the conformation of the assembled capsid, nor of individual CP molecules. The loop is part of a positively charged pocket that includes a previously identified determinant of transmission. We propose that this pocket is a ligand-binding site with essential function in GFLV transmission by X. index. Our data suggest that perturbation of the electrostatic landscape of this pocket affects the interaction of the virion with specific receptors of the nematode's feeding apparatus, and thereby severely diminishes its transmission efficiency. These data provide a first structural insight into the interactions between a plant virus and a nematode vector

Activités d'éveil scientifiques à l'école élémentaire - 2 : première approche des problèmes écologiques

Est-il possible, est-il utile de donner une formation écologique aux jeunes enfants ? Comment peut-on développer très tôt une prise de conscience des responsabilités de l'homme vis-à-vis de son environnement ? Une éducation des comportements individuels pourra-t-elle permettre une exploitation rationnelle des ressources naturelles ? Les équipes de recherche du Service d'Etudes et de Recherches Pédagogiques de l'I.N.R.D.P. (section « activités d'éveil scientifiques à l'école élémentaire ») proposent des éléments de réponse à ces questions en présentant un compte rendu des travaux conduits dans plus d'une centaine de classes expérimentales. L'initiation écologique ne peut dépasser le niveau du conditionnement, du matraquage publicitaire que si elle se situe dans une perspective d'éducation générale telle qu'elle est définie actuellement dans le cadre général des activités d'éveil. D'autre part, elle est inséparable de l'acquisition de certaines compétences scientifiques — méthodes et connaissances — acquises au cours d'une démarche de découverte et formulées selon le niveau de développement de l'enfant. Pour ces deux raisons, ce numéro de la Recherche Pédagogique est le prolongement direct du n° 62 « Activités d'éveil scientifiques - I. Objectifs, méthodes et moyens ».287 pages, figures, tableau

Grapevine Resistance to the Nematode Xiphinema index

Breeding for varieties carrying natural resistance (R) against plant-parasitic nematodes is a promising alternative to nematicide ban. In perennial crops, the long plant-nematode interaction increases the risk for R breaking and R durability is a real challenge. In grapevine, the nematode has a high economic impact by transmitting (GFLV) and, to delay GFLV transmission, rootstocks resistant to this vector are being selected, using in particular as an R source. To optimize this strategy, the durability has been studied under controlled conditions in F1 and BC1 muscadine-derived resistant accessions previously obtained from either hardwood-cutting or in vitro propagation. After inoculation with a mix, in equal proportions, of four lines representative of the diversity, multiplication on plants has been monitored 3 to 6 years. The nematode reproduction factor remained lower than 1 in resistant plants obtained from hardwood cuttings while it increased at values far beyond 1 in resistant plants of in vitro origin. Data for nematode numbers per gram of roots mostly paralleled those obtained for the reproduction factor. The effect of the propagation type on resistance over years was also evaluated for the ratio female/juvenile and the frequency of males. Altogether our results illustrate that the muscadine-derived resistance based on hardwood cuttings is durable. By contrast, in resistant and reference accessions obtained from in vitro, our data suggest that the increased nematode multiplication might be mainly due to the modification of root architecture consecutive to this propagation method