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.

Genetics and Biochemistry of Zero-Tannin Lentils

“…rapa . However, the amounts of mRNA for DFR , anthocyanidin synthase ( ANS ), and anthocyanidin reductase ( ANR ) are not statistically significant in transparent seed coat phenotypes [31]. Arabidopsis thaliana tt3 mutant seeds have transparent seed coats, and visible anthocyanidins or proanthocyanidins are not detected in the tt3 mutant because it lacks DFR mRNA [32].…”

Regulation of anthocyanin and proanthocyanidin biosynthesis by Medicago truncatula bHLH transcription factor MtTT8

“…S1; Notes S1). Distance analysis revealed that these bHLH transcription factors, including Arabidopsis TT8, BrTT8 (Brassica rapa), are clustered in an AN1/TT8 clade (Li et al, 2012). Less identity was seen with potential monocot orthologs such as maize IN1 and rice Rc (Fig.…”

The effect of transposable elements on phenotypic variation: insights from plants to humans

“…Cs1 excision from Y causes the pericarp to revert to red (Chopra et al, 1999). TE-mediated insertional mutations also cause alterations of seed coat color and flower color in Ipomoea purpurea (Clegg and Durbin, 2000;Park et al, 2007), changes in seed coat color in Brassica rapa , changes in hull and internode color in rice (Hong et al, 2012), and differences in grape skin color (Kobayashi et al, 2004).…”