GENOME-WIDE ASSOCIATION MAPPING OF PHENOLIC ACIDS COMPOUNDS IN DURUM WHEATS

Phenolic acids are major components of cell walls in wheat and have important implications on human health as antioxidants with anti-tumor activity. Understanding the genetic basis of phenolic acids content and composition of wheat grain, and identifying associated markers provide the basis for improving wheat quality by molecular breeding. The objective of this study was: a) to identify phenolic acids genes in wheat by exploiting genomic resources and SNPs detected within the coding sequences of candidate genes; and b) to identify chromosomal regions associated to single phenolic acids and total soluble phenolic compounds by genome-wide association study (GWAS) and candidate gene approaches using a tetraploid wheat collection coupled with the 90K iSelect SNP genotyping array. A set of candidate genes involved in the biosynthesis of hydroxycinnamic acid derivatives (p-coumaric acid, ferulic acid and sinapic acid) and in the total soluble phenolics have been identified in wheat by comparative genomics. Single nucleotide polymorphisms (SNPs) found in the coding sequences of six candidate genes (PAL1, PAL2, C4H, C3H, COMT1 and COMT2) allowed to determine their chromosomal location and accurate map position on two reference consensus linkage maps. The genome-wide association study based on genotyping a tetraploid wheat collection with 81,587 gene-associated SNPs revealed several significant marker-trait associations, identifying 22 quantitative trait loci (QTLs) associated with individual phenolic acids and total soluble phenol compounds distributed on almost all durum wheat chromosomes. A QTL for p-coumaric acid was found to be coincident with the candidate gene phenylalanine ammonia-lyase (PAL2) on chromosome arm 2AL. The availability of perfect, candidate gene-based markers can allow elucidating the mechanism of phenol acids accumulation in the wheat kernels and exploiting the genetic variability of phenol acids content for the nutritional improvement of wheat end-products.