No abstract

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 leucine aminopeptidase (EC 3.4.11.1) cDNA clone (DR57) that was induced in response to Pseudomonas syringae pv. tomato (P.s. tomato) infection was isolated using a subtractive hybridization-enriched cDNA probe. Genomic DNA blot analysis showed that the tomato genome had two leucine aminopeptidase genes. The levels of DR57 mRNAs after P.s. tomato infection and mechanical wounding were determined in two inbred tomato lines that exhibit susceptibility and resistance to P.s. tomato. DR57 mRNAs were detected 12 hours after infection and 4 hours after wounding. Furthermore, DR57 mRNAs were systemically induced in response to wounding. DR57 mRNAs were induced in leaves after Spodoptera littoralis feeding but were not detected in detached leaf controls. Possible roles for the DR57 leucine aminopeptidase in the defense reactions are discussed.In response to pathogen invasion, a large number of plant genes coding for proteins involved in the creation and deposition of physical barriers and development of mechanisms that actively antagonize pathogen growth are induced (for reviews, see refs.

Genotyping by sequencing (GBS) provides opportunities to generate high-resolution genetic maps at a low genotyping cost, but for highly heterozygous species, missing data and heterozygote undercalling complicate the creation of GBS genetic maps. To overcome these issues, we developed a publicly available, modular approach called HetMappS, which functions independently of parental genotypes and corrects for genotyping errors associated with heterozygosity. For linkage group formation, HetMappS includes both a reference-guided synteny pipeline and a reference-independent de novo pipeline. The de novo pipeline can be utilized for under-characterized or high diversity families that lack an appropriate reference. We applied both HetMappS pipelines in five half-sib F1 families involving genetically diverse Vitis spp. Starting with at least 116,466 putative SNPs per family, the HetMappS pipelines identified 10,440 to 17,267 phased pseudo-testcross (Pt) markers and generated high-confidence maps. Pt marker density exceeded crossover resolution in all cases; up to 5,560 non-redundant markers were used to generate parental maps ranging from 1,047 cM to 1,696 cM. The number of markers used was strongly correlated with family size in both de novo and synteny maps (r = 0.92 and 0.91, respectively). Comparisons between allele and tag frequencies suggested that many markers were in tandem repeats and mapped as single loci, while markers in regions of more than two repeats were removed during map curation. Both pipelines generated similar genetic maps, and genetic order was strongly correlated with the reference genome physical order in all cases. Independently created genetic maps from shared parents exhibited nearly identical results. Flower sex was mapped in three families and correctly localized to the known sex locus in all cases. The HetMappS pipeline could have wide application for genetic mapping in highly heterozygous species, and its modularity provides opportunities to adapt portions of the pipeline to other family types, genotyping technologies or applications.

Bud dormancy and cold hardiness are critical adaptations for surviving winter cold stress for temperate perennial plant species. In grapevine, acquisition of cold hardiness requires dormancy induction in the early winter and careful maintenance of dormancy state throughout winter. With sufficient exposure to low, non-freezing temperatures (chilling requirement), grapevine buds transition between early (endodormant) and late winter (ecodormant) states. The objective of this study was to uncover the relationship between fulfilment of the chilling requirement and the effects of various temperatures on loss of cold hardiness (deacclimation). The relationship between chilling requirement and temperature as it affects the rate of deacclimation ( k deacc ) was examined for dormant cuttings of Vitis vinifera , V. aestivalis , V. amurensis and V. riparia . The effect of temperature on k deacc was exponential at low and logarithmic at high temperatures. Deacclimation rates also increased in magnitude as chilling accumulated demonstrating a change in deacclimation potential (Ψ deacc ), following a logarithmic response. The combination of Ψ deacc and k deacc indicates genotype-specific thermal efficiency for deacclimation and growth in Vitis that may be overlooked by simple growing degree-day computations. The Ψ deacc and k deacc parameters are genotype-specific and will greatly increase the refinement of models predicting effects of climate change on phenology. Deacclimation rates represent a quantitative determinant of dormancy transition and budbreak in grapevine and will assist researchers in selecting germplasm for differences in chilling requirement and thermal efficiency.