Cell-to-cell progression of tobacco mosaic virus (TMV) infection in plants depends on virus-encoded movement protein (MP). Here we show that a conserved sequence motif in tobamovirus MPs shares similarity with a region in tubulins that is proposed to mediate lateral contacts between microtubule protofilaments. Point mutations in this motif confer temperature sensitivity to microtubule association and viral-RNA intercellular-transport functions of the protein, indicating that MP-interacting microtubules are functionally involved in the transport of vRNA to plasmodesmata. Moreover, we show that MP interacts with microtubule-nucleation sites. Together, our results indicate that MP may mimic tubulin assembly surfaces to propel vRNA transport by a dynamic process that is driven by microtubule polymerization.

Background: In traditional vine areas, the production should present a typicity that partly depends on the grapevine variety. Therefore, vine improvement is considered difficult because of the limited choice in the natural variability of the cultivars within the limits of their characteristics. A possibility to circumvent this problem is the use of somatic variability. In vitro somatic embryogenesis and organogenesis can lead to genotypic and phenotypic variations, described as somaclonal variation, that could be useful for the selection of improved grapevine genotypes.

BackgroundGenes belonging to the pathogenesis related 10 (PR10) group have been studied in several plant species, where they form multigene families. Until now, such an analysis has not been performed in Vitis vinifera, although three different PR10 genes were found to be expressed under pathogen attack or abiotic stress, and during somatic embryogenesis induction. We used the complete genome sequence for characterising the whole V. vinifera PR10 gene family. The expression of candidate genes was studied in various non-treated tissues and following somatic embryogenesis induction by the auxin 2,4-D.ResultsIn addition to the three V. vinifera PR10 genes already described, namely VvPR10.1, VvPR10.2 and VvPR10.3, fourteen different PR10 related sequences were identified. Showing high similarity, they form a single cluster on the chromosome 5 comprising three pseudogenes. The expression of nine different genes was detected in various tissues. Although differentially expressed in non-treated plant organs, several genes were up-regulated in tissues treated with 2,4-D, as expected for PR genes.ConclusionsPR10 genes form a multigene family in V. vinifera, as found in birch, apple or peach. Seventeen closely related PR10 sequences are arranged in a tandem array on the chromosome 5, probably reflecting small-scale duplications during evolution. Various expression patterns were found for nine studied genes, highlighting functional diversification. A phylogenetic comparison of deduced proteins with PR10 proteins of other plants showed a characteristic low intraspecific variability. Particularly, a group of seven close tandem duplicates including VvPR10.1, VvPR10.2 and VvPR10.3 showed a very high similarity, suggesting concerted evolution or/and recent duplications.

Little is known about the genes expressed during grapevine somatic embryogenesis. Both groups of Somatic Embryogenesis Receptor Kinase (SERK) and Leafy Cotyledon (LEC and L1L) genes seem to play key roles during somatic embryogenesis in various plant species. Therefore, we identified and analysed the sequences of VvSERK and VvL1L (Leafy cotyledon1-Like) genes. The deduced amino acid sequences of VvSERK1, VvSERK2 and VvSERK3 are very similar to that of registered SERK proteins, with highest homologies for the kinase domain in the C-terminal region. The amino acid sequence of VvL1L presents all the domains that are characteristic for LEC1 and L1L proteins, particularly, the 16 amino acid residues that serve as signature of the B-domain. Phylogenetic analysis distinguishes members of subclass LEC1 and subclass L1L, and VvL1L is closely related to L1L proteins. Using semi-quantitative RT-PCR, we studied gene expression of VvSERK1, VvSERK2, VvSERK3 and VvL1L in calli and somatic embryos obtained from anther culture of Vitis vinifera L. cv Chardonnay. Expression of VvSERK2 is relatively stable during in vitro culture. In contrast, VvSERK1, VvSERK3 and VvL1L are expressed more 4 to 6 weeks after transfer of the calli onto embryo induction medium, before the visible appearance of embryos on the calli as seen by environmental scanning electron microscopy. Later on (8 weeks after transfer) VvSERK1 expression is maintained in the embryogenic calli and VvSERK3 in the embryos, whereas VvL1L expression is very low. All together, these data suggest the involvement of VvSERK and VvL1L genes in grapevine somatic embryogenesis.

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