Abstract

Key message A novel quantitative trait locus for early flowering in spring oilseed rape, BnaC08cqDTF , was mapped to an 86-kb region on chromosome C08, and its causal gene, CRY2 , was uncovered. Abstract Days to flowering is a very important agronomic and adaptive trait of Brassica napus oilseed rape (AACC, 2 n  = 38). We previously identified BnaC08cqDTF as a novel candidate quantitative trait locus (QTL) for early flowering in spring oilseed rape. Here, we present fine mapping of the locus and a study of its causal gene. Initial mapping was performed by QTL sequencing of DNA pools of BC 3 F 2 plants with extreme flowering times derived from crosses between the spring-type cv. No. 4512 (early flowering) and cv. No. 5246 (late flowering), along with fine mapping by target sequencing of the BC 3 F 2 and BC 4 F 2  populations. Fine mapping narrowed down BnaC08cqDTF to an 86-kb region on chromosome C08. The region harbored fifteen genes. After comparative analyses of the DNA sequences for mutation between A and C syntenic regions and detected by RNA-seq and qRT-PCR between the two parents, we found that BnaC08G0010400ZS harbors an A/G nonsynonymous mutation in exon 3. This single nucleotide polymorphism (SNP) haplotype was also correlated with early flowering in a 256 accession panel. BnaC08G0010400ZS is a homolog of the AT1G04400 gene ( CRY2 ) in Arabidopsis . The analyses of transgenic Arabidopsis verified that BnaC08G0010400ZS is responsible for early flowering. Our results contribute to a better understanding of the genetic control mechanism of early flowering in spring Brassica napus and will promote the breeding for early mature varieties.