Abstract
The proanthocyanidin (PA) is the main flavonoids which affect the seed coat color in Brassica species. In this paper, characteristics of color development and accumulation of flavonoids were analyzed in the seeds of brown-seeded (B147) and yellow-seeded (B80) heading Chinese cabbage (Brassica rapa L. ssp. Pekinensis). It is found that the content of phenolic compounds in B147 were significantly more than that of B80 by using dimethylaminocinnamaldehyde (DMACA) staining and toluidine blue O (TBO) staining. In previous studies, the locus associated with seed coat color has been mapped. The results of whole genome re-sequencing showed that there are large fragment deletions variation in the mapping region between the brown-seeded parent ‘92S105’ and the yellow-seeded parent ‘91-125.’ Based on the B. rapa genome annotation information, the TRANSPARENT TESTA GLABRA 1 (TTG1), is likely to be the candidate gene controlling seed coat color. A 94-base deletion was found in the 96th base downstream of the initiation codon in the TTG1 of yellow seed, thus, the termination codon TGA was occurred in the 297th base which makes the full length of TTG1 of yellow seed is 300 bp. Based on the differential sequences of TTG1 of brown and yellow seed, a functional marker, Brsc-yettg1, was developed to detect the variation of TTG1. Quantitative real-time PCR analysis of BrTTG1 in different tissues showed that expression levels of BrTTG1 was not tissue-specific. During the whole seed development period, the expression of BrTTG1 in B147 was higher than that of B80. The expression levels of four structural genes, BrDFR, BrANS, BrANR1, and BrANR2 in B147 were also higher than those in B80. The co-segregation molecular markers obtained in this report and TTG1 related information provide a basis for further understanding of the molecular mechanism of seed coat color in heading Chinese cabbage.
Highlights
Yellow seed coat and brown seed coat are two kinds of seed coat color which were universally existed in Chinese cabbage
The expression of BrANR1 and BrANR2 in B147 were nearly 500-fold and 50-fold higher than those in B80, respectively. All these results indicated that the TTG1Y mutation seriously debased the transcript level of late biosynthetic genes (LBGs) in flavonoids pathway, and maybe results in the formation of yellow seed coat
In Brassicaceae, Lepiniec et al (2006) reported that the formation of brown seed coat was due to the accumulation of PAs in the endothelium layer of the inner integument
Summary
Yellow seed coat and brown seed coat are two kinds of seed coat color which were universally existed in Chinese cabbage Proanthocyanidins (PAs), the oligomeric and polymeric end products synthesized via the flavonoid biosynthesis pathway (Winkel-Shirley, 2001; Dixon et al, 2005), are commonly found in the plant kingdom and generally have protective effects on predation and pathogen attack (Scalbert, 1991; Harborne and Grayer, 1993). Their beneficial effects on human health have been demonstrated in several studies (Bagchi et al, 2000; Manach et al, 2005; Georgiev et al, 2014). In Brassicaceae, PAs were accumulated in the endothelium layer of the inner integument of seed coat, which caused the formation of brown seed coat color (Lepiniec et al, 2006)
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