A candidate gene association study on muscat flavor in grapevine (Vitis vinifera L.).
BACKGROUND
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 (Vitis vinifera 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 (VvDXS) with the major QTL positioned on chromosome 5.


RESULTS
We resequenced VvDXS in an ad hoc 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.


CONCLUSIONS
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. VvDXS 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.
Research and Innovation Center, Fondazione Edmund Mach-Istituto Agrario di San Michele all'Adige, Via E, Mach 1, 38010 San Michele all'Adige (TN), Italy. francesco.emanuelli@iasma.it
Francesco
F
Emanuelli
Juri
J
Battilana
Laura
L
Costantini
Loïc
L
Le Cunff
Jean-Michel
JM
Boursiquot
Patrice
P
This
Maria S
MS
Grando
D019747:Aldose-Ketose Isomerases / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D005787:Gene Frequency; D017343:Genes, Plant / Q000235:genetics*; D014644:Genetic Variation; D005838:Genotype; D006239:Haplotypes; D015810:Linkage Disequilibrium; D008969:Molecular Sequence Data; D039821:Monoterpenes / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013649:Taste; D027843:Vitis / Q000145:classification / Q000235:genetics* / Q000378:metabolism*
D039821:Monoterpenes; D009097:Multienzyme Complexes; D010940:Plant Proteins; D010088:Oxidoreductases; C114231:1-deoxy-D-xylulose 5-phosphate reductoisomerase; D019747:Aldose-Ketose Isomerases