The hypersensitive reaction to a pathogen is one of the most efficient defense mechanisms in nature and leads to the induction of numerous plant genes encoding defense proteins. These proteins include: 1) structural proteins that are incorporated into the extracellular matrix and participate in the confinement of the pathogen; 2) enzymes of secondary metabolism, for instance those of the biosynthesis of plant antibiotics; 3) pathogenesis-related (PR) proteins which represent major quantitative changes in soluble protein during the defense response. The PRs have typical physicochemical properties that enable them to resist to acidic pH and proteolytic cleavage and thus survive in the harsh environments where they occur: vacuolar compartment or cell wall or intercellular spaces. Since the discovery of the first PRs in tobacco many other similar proteins have been isolated from tobacco but also from other plant species, including dicots and monocots, the widest range being characterized from hypersensitively reacting tobacco. Based first on serological properties and later on sequence data, the tobacco PRs have been classified in five major groups. Group PR-1 contains the first discovered PRs of 15-17 kDa molecular mass, whose biological activity is still unknown, but some members have been shown recently to have antifungal activity. Group PR-2 contains three structurally distinct classes of 1,3-beta-glucanases, with acidic and basic counterparts, with dramatically different specific activity towards linear 1,3-beta-glucans and with different substrate specificity. Group PR-3 consists of various chitinases-lysozymes that belong to three distinct classes, are vacuolar or extracellular, and exhibit differential chitinase and lysozyme activities. Some of them, either alone or in combination with 1,3-beta-glucanases, have been shown to be antifungal in vitro and in vivo (transgenic plants), probably by hydrolysing their substrates as structural components in the fungal cell wall. Group PR-4 is the less studied, and in tobacco contains four members of 13-14.5 kDa of unknown activity and function. Group PR-5 contains acidic-neutral and very basic members with extracellular and vacuolar localization, respectively, and all members show sequence similarity to the sweet-tasting protein thaumatin. Several members of the PR-5 group from tobacco and other plant species were shown to display significant in vitro activity of inhibiting hyphal growth or spore germination of various fungi probably by a membrane permeabilizing mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)

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SUMMARYThe most economically important diseases of grapevine cultivation worldwide are caused by the fungal pathogen powdery mildew (Erysiphe necator syn. Uncinula necator) and the oomycete pathogen downy mildew (Plasmopara viticola). Currently, grapegrowers rely heavily on the use of agrochemicals to minimize the potentially devastating impact of these pathogens on grape yield and quality. The wild North American grapevine species Muscadinia rotundifolia was recognized as early as 1889 to be resistant to both powdery and downy mildew. We have now mapped resistance to these two mildew pathogens in M. rotundifolia to a single locus on chromosome 12 that contains a family of seven TIR-NB-LRR genes. We further demonstrate that two highly homologous (86% amino acid identity) members of this gene family confer strong resistance to these unrelated pathogens following genetic transformation into susceptible Vitis vinifera winegrape cultivars. These two genes, designated resistance to Uncinula necator (MrRUN1) and resistance to Plasmopara viticola (MrRPV1) are the first resistance genes to be cloned from a grapevine species. Both MrRUN1 and MrRPV1 were found to confer resistance to multiple powdery and downy mildew isolates from France, North America and Australia; however, a single powdery mildew isolate collected from the southeastern region of North America, to which M. rotundifolia is native, was capable of breaking MrRUN1-mediated resistance. Comparisons of gene organization and coding sequences between M. rotundifolia and the cultivated grapevine V. vinifera at the MrRUN1/MrRPV1 locus revealed a high level of synteny, suggesting that the TIR-NB-LRR genes at this locus share a common ancestor.

A genetic linkage map of grapevine was constructed using a pseudo-testcross strategy based upon 138 individuals derived from a cross of Vitis vinifera Cabernet Sauvignon x Vitis riparia Gloire de Montpellier. A total of 212 DNA markers including 199 single sequence repeats (SSRs), 11 single strand conformation polymorphisms (SSCPs) and two morphological markers were mapped onto 19 linkage groups (LG) which covered 1,249 cM with an average of 6.7 cM between markers. The position of SSR loci in the maps presented here is consistent with the genome sequence. Quantitative traits loci (QTLs) for several traits of inflorescence and flower morphology, and downy mildew resistance were investigated. Two novel QTLs for downy mildew resistance were mapped on linkage groups 9 and 12, they explain 26.0-34.4 and 28.9-31.5% of total variance, respectively. QTLs for inflorescence morphology with a large effect (14-70% of total variance explained) were detected close to the Sex locus on LG 2. The gene of the enzyme 1-aminocyclopropane-1-carboxylic acid synthase, involved in melon male organ development and located in the confidence interval of all QTLs detected on the LG 2, could be considered as a putative candidate gene for the control of sexual traits in grapevine. Co-localisations were found between four QTLs, detected on linkage groups 1, 14, 17 and 18, and the position of the floral organ development genes GIBBERELLIN INSENSITIVE1, FRUITFULL, LEAFY and AGAMOUS. Our results demonstrate that the sex determinism locus also determines both flower and inflorescence morphological traits.