Genome-wide association mapping for phenolic acids concentration and composition in a collection of tetraploid wheats

Phenolic acids are major components of plant cell walls in wheat and have important implications on human health as antioxidants with anti-tumor activity. They occur in wheat grains as: i) soluble free phenolic acids; ii) soluble conjugated phenolics bound to low molecular mass components such as saccharides or organic acids; iii) insoluble bound forms of phenolics, linked to polymers of the plant cell wall (Li et al., 2008). Despite their high value for human health, few studies have been carried out on the genetics of phenolic acids in durum wheat. The genetic variability of phenolic acids composition and concentration was investigated, over two years, in a set of 111 tetraploid wheat genotypes, belonging to seven Triticum turgidum L. subspecies, including cultivars, landraces and wild accessions. Regions attributable to individual phenolic acids and total phenolic acids concentration were identified through a genome wide association study (GWAS). A total of six phenolic acids were identified by DAD-HPLC analysis across the 111 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 (Laddomada et al, 2016). The soluble free fraction (measured spectrophotometrically after Folin Ciocalteu reaction) ranged from 1280 to 3150 ?g g-1 as ferulic acid equivalents. The effects of genotype, year and year x genotype were estimated by ANOVA and resulted significant for all phenolic acids. The ratio of genotypic variance to total variance was moderately high suggesting that a breeding approach could be considered to increase phenolic acids concentration in durum wheat. The GWAS revealed a total of 29 significant marker-trait associations (MTA), identifying eight quantitative trait loci (QTL) associated with phenolic acids content. The highest number of MTAs was identified on chromosome 7A, where one QTL region was associated with phenolic acids content, while the lowest number of MTAs was detected on chromosomes 3A and 5B, where only one MTA identified a single locus. Conservation of synteny between SNP marker sequences 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.