Functional effect of grapevine 1-deoxy-D-xylulose 5-phosphate synthase substitution K284N on Muscat flavour formation

Grape berries of Muscat cultivars (Vitis vinifera L.) contain high levels of monoterpenols and exhibit a distinct aroma related to this composition of volatiles. A structural gene of the plastidial methyl-erythritol-phosphate (MEP) pathway, 1-deoxy-D-xylulose 5-phosphate synthase (VvDXS), was recently suggested as a candidate gene for this trait, having been co-localized with a major quantitative trait locus for linalool, nerol, and geraniol concentrations in berries. In addition, a structured association study discovered a putative causal single nucleotide polymorphism (SNP) responsible for the substitution of a lysine with an asparagine at position 284 of the VvDXS protein, and this SNP was significantly associated with Muscat-flavoured varieties. The significance of this nucleotide difference was investigated by comparing the monoterpene profiles with the expression of VvDXS alleles throughout berry development in Moscato Bianco, a cultivar heterozygous for the SNP mutation. Although correlation was detected between the VvDXS transcript profile and the accumulation of free monoterpenol odorants, the modulation of VvDXS expression during berry development appears to be independent of nucleotide variation in the coding sequence. In order to assess how the non-synonymous mutation may enhance Muscat flavour, an in vitro characterization of enzyme isoforms was performed followed by in vivo overexpression of each VvDXS allele in tobacco. The results showed that the amino acid non-neutral substitution influences the enzyme kinetics by increasing the catalytic efficiency and also dramatically affects monoterpene levels in transgenic lines. These findings confirm a functional effect of the VvDXS gene polymorphism and may pave the way for metabolic engineering of terpenoid contents in grapevine

Regulation of flavonol content and composition in (Syrah×Pinot Noir) mature grapes: integration of transcriptional profiling and metabolic quantitative trait locus analyses

8openInternationalFlavonols are a ubiquitous class of flavonoids that accumulate preferentially in flowers and mature berries. Besides their photo-protective function, they play a fundamental role during winemaking, stabilizing the colour by co-pigmentation with anthocyanins and contributing to organoleptic characteristics. Although the general flavonol pathway has been genetically and biochemically elucidated, the genetic control of flavonol content and composition at harvest is still not clear. To this purpose, the grapes of 170 segregating F1 individuals from a ‘Syrah’×’Pinot Noir’ population were evaluated at the mature stage for the content of six flavonol aglycons in four seasons. Metabolic data in combination with genetic data enabled the identification of 16 mQTLs (metabolic quantitative trait loci). For the first time, major genetic control by the linkage group 2 (LG 2)/MYBA region on flavonol variation, in particular of tri-hydroxylated flavonols, is demonstrated. Moreover, seven regions specifically associated with the fine control of flavonol biosynthesis are identified. Gene expression profiling of two groups of individuals significantly divergent for their skin flavonol content identified a large set of differentially modulated transcripts. Among these, the transcripts coding for MYB and bZIP transcription factors, methyltranferases, and glucosyltranferases specific for flavonols, proteins, and factors belonging to the UV-B signalling pathway and co-localizing with the QTL regions are proposed as candidate genes for the fine regulation of flavonol content and composition in mature grapesopenMalacarne, G.; Costantini, L.; Coller, E.; Battilana, J.; Velasco, R.; Vrhovsek, U.; Grando, M.S.; Moser, C.Malacarne, G.; Costantini, L.; Coller, E.; Battilana, J.; Velasco, R.; Vrhovsek, U.; Grando, M.S.; Moser, C

Berry and phenology-related traits in grapevine (<it>Vitis vinifera </it>L.): From Quantitative Trait Loci to underlying genes

Abstract Background The timing of grape ripening initiation, length of maturation period, berry size and seed content are target traits in viticulture. The availability of early and late ripening varieties is desirable for staggering harvest along growing season, expanding production towards periods when the fruit gets a higher value in the market and ensuring an optimal plant adaptation to climatic and geographic conditions. Berry size determines grape productivity; seedlessness is especially demanded in the table grape market and is negatively correlated to fruit size. These traits result from complex developmental processes modified by genetic, physiological and environmental factors. In order to elucidate their genetic determinism we carried out a quantitative analysis in a 163 individuals-F1 segregating progeny obtained by crossing two table grape cultivars. Results Molecular linkage maps covering most of the genome (2n = 38 for Vitis vinifera) were generated for each parent. Eighteen pairs of homologous groups were integrated into a consensus map spanning over 1426 cM with 341 markers (mainly microsatellite, AFLP and EST-derived markers) and an average map distance between loci of 4.2 cM. Segregating traits were evaluated in three growing seasons by recording flowering, veraison and ripening dates and by measuring berry size, seed number and weight. QTL (Quantitative Trait Loci) analysis was carried out based on single marker and interval mapping methods. QTLs were identified for all but one of the studied traits, a number of them steadily over more than one year. Clusters of QTLs for different characters were detected, suggesting linkage or pleiotropic effects of loci, as well as regions affecting specific traits. The most interesting QTLs were investigated at the gene level through a bioinformatic analysis of the underlying Pinot noir genomic sequence. Conclusion Our results revealed novel insights into the genetic control of relevant grapevine features. They provide a basis for performing marker-assisted selection and testing the role of specific genes in trait variation.</p

A candidate gene association study on muscat flavor in grapevine (<it>Vitis vinifera </it>L.)

<p>Abstract</p> <p>Background</p> <p>The sweet, floral flavor typical of Muscat varieties (Muscats), due to high levels of monoterpenoids (geraniol, linalool and nerol), is highly distinct and has been greatly appreciated both in table grapes and in wine since ancient times. Muscat flavor determination in grape (<it>Vitis vinifera </it>L.) has up to now been studied by evaluating monoterpenoid levels through QTL analysis. These studies have revealed co-localization of 1-deoxy-D-xylulose 5-phosphate synthase (<it>VvDXS</it>) with the major QTL positioned on chromosome 5.</p> <p>Results</p> <p>We resequenced <it>VvDXS </it>in an <it>ad hoc </it>association population of 148 grape varieties, which included muscat-flavored, aromatic and neutral accessions as well as muscat-like aromatic mutants and non-aromatic offsprings of Muscats. Gene nucleotide diversity and intragenic linkage disequilibrium (LD) were evaluated. Structured association analysis revealed three SNPs in moderate LD to be significantly associated with muscat-flavored varieties. We identified a putative causal SNP responsible for a predicted non-neutral substitution and we discuss its possible implications for flavor metabolism. Network analysis revealed a major star-shaped cluster of reconstructed haplotypes unique to muscat-flavored varieties. Moreover, muscat-like aromatic mutants displayed unique non-synonymous mutations near the mutated site of Muscat genotypes.</p> <p>Conclusions</p> <p>This study is a crucial step forward in understanding the genetic regulation of muscat flavor in grapevine and it also sheds light on the domestication history of Muscats. <it>VvDXS </it>appears to be a possible human-selected locus in grapevine domestication and post-domestication. The putative causal SNP identified in Muscat varieties as well as the unique mutations identifying the muscat-like aromatic mutants under study may be immediately applied in marker-assisted breeding programs aimed at enhancing fragrance and aroma complexity respectively in table grape and wine cultivars.</p

Berry and phenology-related traits in grapevine (L.): From Quantitative Trait Loci to underlying genes-0

He left (Italia) and right (Big Perlon) and the consensus map is in the centre. Markers common between parental and consensus maps are indicated by lines. Distorted markers have an asterisk showing the level of distortion (* = P ≤ 0.1, ** = P ≤ 0.05, *** = P ≤ 0.01; **** = P ≤ 0.005; ***** = P ≤ 0.001; ****** = P ≤ 0.0005; ******* = P ≤ 0.0001). Underlined markers are EST-based markers analyzed in the progeny Moscato bianco × and mapped for synteny in the maps of Italia and Big Perlon. Distances of markers from the top are indicated on the left in cM Kosambi.<p><b>Copyright information:</b></p><p>Taken from "Berry and phenology-related traits in grapevine (L.): From Quantitative Trait Loci to underlying genes"</p><p>http://www.biomedcentral.com/1471-2229/8/38</p><p>BMC Plant Biology 2008;8():38-38.</p><p>Published online 17 Apr 2008</p><p>PMCID:PMC2395262.</p><p></p

Regulation of flavonol content and composition in (Syrah×Pinot Noir) mature grapes: integration of transcriptional profiling and metabolic quantitative trait locus analyses

Flavonols are a ubiquitous class of flavonoids that accumulate preferentially in flowers and mature berries. Besides their photo-protective function, they play a fundamental role during winemaking, stabilizing the colour by co-pigmentation with anthocyanins and contributing to organoleptic characteristics. Although the general flavonol pathway has been genetically and biochemically elucidated, the genetic control of flavonol content and composition at harvest is still not clear. To this purpose, the grapes of 170 segregating F1 individuals from a ‘Syrah’×’Pinot Noir’ population were evaluated at the mature stage for the content of six flavonol aglycons in four seasons. Metabolic data in combination with genetic data enabled the identification of 16 mQTLs (metabolic quantitative trait loci). For the first time, major genetic control by the linkage group 2 (LG 2)/MYBA region on flavonol variation, in particular of tri-hydroxylated flavonols, is demonstrated. Moreover, seven regions specifically associated with the fine control of flavonol biosynthesis are identified. Gene expression profiling of two groups of individuals significantly divergent for their skin flavonol content identified a large set of differentially modulated transcripts. Among these, the transcripts coding for MYB and bZIP transcription factors, methyltranferases, and glucosyltranferases specific for flavonols, proteins, and factors belonging to the UV-B signalling pathway and co-localizing with the QTL regions are proposed as candidate genes for the fine regulation of flavonol content and composition in mature grape