Mapping Quantitative Traits Loci for Seed Glucosinolate Content inBrassica napusUsing High-density SNP Map

Fine mapping and candidate gene analysis of a seed glucosinolate content QTL, qGSL-C2, in rapeseed (Brassica napus L.)

QTL mapping and candidate gene analysis indicate that allelic variations in BnaC2.MYB28 resulted from homeologous exchange and determine difference in seed glucosinolate content. A low seed glucosinolate content has long been an important breeding objective in rapeseed improvement. However, the molecular mechanisms underlying seed GSL content variations remain to be elucidated in allotetraploid Brassica napus. Here, we developed a double haploid population from a cross between two B. napus accessions that possess relatively low, but significantly different seed GSL contents and identified a major QTL, qGSL-C2, on chromosome C02 that explains 30.88-72.87% of the phenotypic variation observed in five environments. Using near-isogenic lines, we further delimited qGSL-C2 to a physical region of 49 kb on the B. rapa chromosome A02 which is highly homologous to the target C02 interval. Among five candidate genes, BnaC2.MYB28, a homologue of the Arabidopsis MYB28 encoding a putative R2R3-MYB-type transcription factor functioning in aliphatic methionine-derived GSL synthesis, was most likely to be the target gene underlying the QTL. Sequence analysis revealed multiple insertion/deletion and SNP variations in the genomic region between the alleles of the NILs. Furthermore, the allelic variations in BnaC2.MYB28 in the natural B. napus population were significantly associated with seed GSL content. Remarkably, the phylogenetic analysis and sequence comparison suggested that while the BnaC2.MYB28 allele from the parental line G120 was inherited from B. oleracea BolC2.MYB28, its counterpart from the other parent, 9172, most likely evolved from B. rapa BraA2.MYB28 via possible homeologous exchange. Our study promotes greater understanding of the molecular regulation of seed GSL content and provides useful molecular markers for seed GSL improvement in B. napus.

Identification of Candidate Genes for Seed Glucosinolate Content Using Association Mapping in Brassica napus L

Rapeseed contains glucosinolates, a toxic group of sulfur-containing glucosides, which play critical roles in defense against herbivores and microbes. However, the presence of glucosinolates in rapeseed reduces the value of the meal as feed for livestock. We performed association mapping of seed glucosinolate (GS) content using the 60K Brassica Infinium single nucleotide polymorphism (SNP) array in 520 oilseed rape accessions. A total of 11 peak SNPs significantly associated with GS content were detected in growing seasons of 2013 and 2014 and were located on B. napus chromosomes A08, A09, C03, and C09, respectively. Two associated regions of GS content covered by these markers were further verified, and three B. napus homologous genes involved in the biosynthesis and accumulation of GS were identified. These genes were multigene family members and were distributed on different chromosomes. Moreover, two genes (BnGRT2 and BnMYB28) associated with GS content were validated by the qRT-PCR analysis of their expression profiles. The further identification and functionalization of these genes will provide useful insight into the mechanism underlying GS biosynthesis and allocation in B. napus, and the associated SNPs markers could be helpful for molecular maker-assisted breeding for low seed GS in B. napus.