Genetic and genomic investigation on phenolic acids in durum wheat

Wheat species contain a variety of polyphenols including phenolic acids, flavonoids, proanthocyanidins, condensed tannins, catechins and lignans. Phenolic acids represent the most common phenolic compounds found in whole wheat grains and can be found as soluble free, soluble conjugated bound to low molecular mass components (e.g. saccharides or organic acids); and insoluble bound forms, linked to polymers of the plant cell wall. Despite their high value for human health, only few studies have been carried out on the genetics and genomics of these bioactive compounds in durum wheat. The objectives of the present work were i) the estimation of genetic variability for phenolic acids composition and concentration in a set of 111 tetraploid wheat genotypes (Triticum turgidum L.), comprising durum cultivars, landraces and wild accessions; and ii) the detection of regions attributable to individual phenolic acids and total phenolic acids concentration by the means of a genome wide association study (GWAS). Phenolic acids were extracted from whole-meal flour and identified by DAD-HPLC analysis. A total of six major phenolic acids were quantified across the durum wheat genotypes, namely: ferulic, sinapic, p-coumaric, vanillic, syringic and p-hydroxibenzoic acids. The amount of total bound phenolic acids, ranged from 341 to 1700 ?g g-1 of whole-meal flour, with a mean value of 800 ?g g-1. The soluble free fraction (measured spectrophotometrically after Folin Ciocalteu reaction) ranged from 1280 to 3150 ?g g-1 as ferulic acid equivalents. The analysis of variance (ANOVA) revealed the effects of genotype, year and year x genotype that were significant for all phenolic acids. The ratio of genotypic variance to total variance was moderately high suggesting that phenolic acids concentration can be further improved by breeding approaches in durum wheat. The GWAS was based on the detection of correlations between genotype and phenotype in the durum germplasm collection by using a high-density wheat SNP iSelect array including approximately 90,000 gene associated SNPs. Results showed several significant marker-trait associations (MTA), identifying eight quantitative trait loci (QTL) associated with phenolic acids concentration. The highest number of MTAs was identified on chromosome 7A, where one QTL region was associated with phenolic acids content. The lowest number of MTAs was detected on chromosomes 3A and 5B, where only one MTA identified a single locus. Conservation of synteny between SNPs and the annotated genes and proteins in Brachypodium distachyon, Oryza sativa and Sorghum bicolor allowed the identification of two QTLs coincident with two different candidate genes.