Abstract
BackgroundProanthocyanidins (PAs), or condensed tannins, are flavonoid polymers, widespread throughout the plant kingdom, which provide protection against herbivores while conferring organoleptic and nutritive values to plant-derived foods, such as wine. However, the genetic basis of qualitative and quantitative PA composition variation is still poorly understood. To elucidate the genetic architecture of the complex grape PA composition, we first carried out quantitative trait locus (QTL) analysis on a 191-individual pseudo-F1 progeny. Three categories of PA variables were assessed: total content, percentages of constitutive subunits and composite ratio variables. For nine functional candidate genes, among which eight co-located with QTLs, we performed association analyses using a diversity panel of 141 grapevine cultivars in order to identify causal SNPs.ResultsMultiple QTL analysis revealed a total of 103 and 43 QTLs, respectively for seed and skin PA variables. Loci were mainly of additive effect while some loci were primarily of dominant effect. Results also showed a large involvement of pairwise epistatic interactions in shaping PA composition. QTLs for PA variables in skin and seeds differed in number, position, involvement of epistatic interaction and allelic effect, thus revealing different genetic determinisms for grape PA composition in seeds and skin. Association results were consistent with QTL analyses in most cases: four out of nine tested candidate genes (VvLAR1, VvMYBPA2, VvCHI1, VvMYBPA1) showed at least one significant association with PA variables, especially VvLAR1 revealed as of great interest for further functional investigation. Some SNP-phenotype associations were observed only in the diversity panel.ConclusionsThis study presents the first QTL analysis on grape berry PA composition with a comparison between skin and seeds, together with an association study. Our results suggest a complex genetic control for PA traits and different genetic architectures for grape PA composition between berry skin and seeds. This work also uncovers novel genomic regions for further investigation in order to increase our knowledge of the genetic basis of PA composition.
Highlights
Proanthocyanidins (PAs), or condensed tannins, are flavonoid polymers, widespread throughout the plant kingdom, which provide protection against herbivores while conferring organoleptic and nutritive values to plant-derived foods, such as wine
PA content variables reached higher values in seeds than in skin regardless of the unit, as illustrated for Total content in mg/g fresh weight (concP) (Figure 2B), which exhibited the largest difference between tissues
All three ratio variables assessing the flux between 2,3-trans and 2,3-cis forms (Ftrancis series) pointed to different kinetics for extension and terminal positions: trans subunits were more abundant in skin for terminal units/monomers (Ftranscis_T) while they were much reduced in seeds when considering extension positions alone (Ftranscis_Ex) or extension plus terminal subunits/monomers (Ftranscis_all, Figure 2D-F)
Summary
Proanthocyanidins (PAs), or condensed tannins, are flavonoid polymers, widespread throughout the plant kingdom, which provide protection against herbivores while conferring organoleptic and nutritive values to plant-derived foods, such as wine. Proanthocyanidins (PAs), or condensed tannins, are flavonoid polymers widespread throughout the plant kingdom They accumulate in many organs and tissues to provide protection against pests [1]. They are determinant in food quality and their beneficial effects on human health are increasingly investigated [1,2]. Few studies are available on the genetic basis of PA composition quantitative variation [6,7]
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