*Article* **Genome-Wide Association Analysis of Mucilage and Hull Content in Flax (***Linum usitatissimum* **L.) Seeds**

**Braulio J. Soto-Cerda 1,\* , Sylvie Cloutier <sup>2</sup> , Rocío Quian <sup>1</sup> , Humberto A. Gajardo <sup>1</sup> , Marcos Olivos <sup>1</sup> and Frank M. You 2,3**


Received: 14 August 2018; Accepted: 18 September 2018; Published: 21 September 2018

**Abstract:** New flaxseed cultivars differing in seed mucilage content (MC) with low hull content (HC) represent an attractive option to simultaneously target the food and feed markets. Here, a genome-wide association study (GWAS) was conducted for MC and HC in 200 diverse flaxseed accessions genotyped with 1.7 million single nucleotide polymorphism (SNP) markers. The data obtained for MC and HC indicated a broad phenotypic variation and high (~70%) and a moderate (~49%) narrow sense heritability, respectively. MC and HC did not differ statistically between fiber and oil morphotypes, but yellow-seeded accessions had 2.7% less HC than brown-seeded ones. The genome-wide linkage disequilibrium (LD) decayed to *r* <sup>2</sup> = 0.1 at a physical distance of ~100 kb. Seven and four quantitative trait loci (QTL) were identified for MC and HC, respectively. Promising candidate genes identified include *Linum usitatissimum* orthologs of the *Arabidopsis thaliana* genes *TRANSPARENT TESTA 8*, *SUBTILISIN-LIKE SERINE PROTEASE*, *GALACTUROSYL TRANSFERASE-LIKE 5*, *MUCILAGE-MODIFIED 4*, *AGAMOUS-LIKE MADS-BOX PROTEIN AGL62*, *GLYCOSYL HYDROLASE FAMILY 17*, and *UDP-GLUCOSE FLAVONOL 3-O-GLUCOSYLTRANSFERASE*. These genes have been shown to play a role in mucilage synthesis and release, seed coat development and anthocyanin biosynthesis in *A. thaliana*. The favorable alleles will be useful in flaxseed breeding towards the goal of achieving the ideal MC and HC composition for food and feed by genomic-based breeding.

**Keywords:** flaxseed; *Linum usitatissimum*; GWAS; seed mucilage content; seed hull content; single nucleotide polymorphism (SNP)
