title: A large insertion in bHLH transcription factor BrTT8 resulting in yellow seed coat in Brassica rapa.
abstract: Yellow seed is a desirable quality trait of the Brassica oilseed species. Previously, several seed coat color genes have been mapped in the Brassica species, but the molecular mechanism is still unknown. In the present investigation, map-based cloning method was used to identify a seed coat color gene, located on A9 in B. rapa. Blast analysis with the Arabidopsis genome showed that there were 22 Arabidopsis genes in this region including at4g09820 to at4g10620. Functional complementation test exhibited a phenotype reversion in the Arabidopsis thaliana tt8-1 mutant and yellow-seeded plant. These results suggested that the candidate gene was a homolog of TRANSPARENT TESTA8 (TT8) locus. BrTT8 regulated the accumulation of proanthocyanidins (PAs) in the seed coat. Sequence analysis of two alleles revealed a large insertion of a new class of transposable elements, Helitron in yellow sarson. In addition, no mRNA expression of BrTT8 was detected in the yellow-seeded line. It indicated that the natural transposon might have caused the loss in function of BrTT8. BrTT8 encodes a basic/helix-loop-helix (bHLH) protein that shares a high degree of similarity with other bHLH proteins in the Brassica. Further expression analysis also revealed that BrTT8 was involved in controlling the late biosynthetic genes (LBGs) of the flavonoid pathway. Our present findings provided with further studies could assist in understanding the molecular mechanism involved in seed coat color formation in Brassica species, which is an important oil yielding quality trait.
authors.affiliation: National Key Laboratory of Crop Genetic Improvement, National Center of Rapeseed Improvement in Wuhan, Huazhong Agricultural University, Wuhan, PR China.
authors.forename: Xia
authors.initials: X
authors.lastname: Li
authors.forename: Li
authors.initials: L
authors.lastname: Chen
authors.forename: Meiyan
authors.initials: M
authors.lastname: Hong
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Feng
authors.initials: F
authors.lastname: Zu
authors.forename: Jing
authors.initials: J
authors.lastname: Wen
authors.forename: Bin
authors.initials: B
authors.lastname: Yi
authors.forename: Chaozhi
authors.initials: C
authors.lastname: Ma
authors.forename: Jinxiong
authors.initials: J
authors.lastname: Shen
authors.forename: Jinxing
authors.initials: J
authors.lastname: Tu
authors.forename: Tingdong
authors.initials: T
authors.lastname: Fu
mesh_terms: D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D029741:Brassica rapa / Q000196:embryology* / Q000235:genetics*; D002874:Chromosome Mapping; D003433:Crosses, Genetic; D018744:DNA, Plant / Q000235:genetics; D005419:Flavonoids / Q000096:biosynthesis; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D056726:Genetic Association Studies; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional / Q000235:genetics*; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010802:Phylogeny; D010858:Pigmentation / Q000235:genetics*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D019655:Quantitative Trait, Heritable; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000196:embryology / Q000235:genetics*
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D018744:DNA, Plant; D005419:Flavonoids; D010940:Plant Proteins; D012333:RNA, Messenger