Characteristics of Color Development in Seeds of Brown- and Yellow-Seeded Heading Chinese Cabbage and Molecular Analysis of Brsc, the Candidate Gene Controlling Seed Coat Color

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.

Identification and validation of major and minor QTLs controlling seed coat color in <i>Brassica rapa</i> L.

“…A09, three minor QTLs on Chr. A06 were detected in this study, and they do not co-localize with a gene ( BrTTG1 ) that was previously identified as being responsible for yellow seed coat color in B. rapa (Ren et al . 2017a, Zhang et al .…”

“…In general, the seed coat color trait is mainly controlled by few genes or major QTLs in B. rapa and brown seed coat color is dominant to yellow seed coats. In recent years, several important genes underlying seed coat color, such as BrTTG1 (Ren et al . 2017a, Zhang et al .…”

Fine mapping of the major QTL for seed coat color in Brassica rapa var. Yellow Sarson by use of NIL populations and transcriptome sequencing for identification of the candidate genes

“…Several studies on seed coat color indicated that a major locus is capable of regulating the formation of seed coat pigments in B . rapa [17, 22, 28, 33, 35, 78]. In the present study, genetic analysis and molecular mapping of seed coat color by use of NILs further supported this, and confirmed the major QTL SCA9-2 located on the chromosome A9.…”

“…Cloning and functional analysis of this gene showed that three missense mutations in BrTT1 are responsible for the yellow seed trait in Dahuang. Zhang et al [22] and Ren et al [35, 36] mapped a major seed coat color locus on A6 (≈R6) of Chinese cabbage ( B . rapa ) and provided evidence that a 94-base deletion in Transparent Testa Glabra1 ( TTG1 ) gene resulted the yellow seed color in this variant of B .…”

Comparative transcriptome and flavonoids components analysis reveal the structural genes responsible for the yellow seed coat color of Brassica rapa L.

“…Seed coat color formation is mainly due to the accumulation of proanthocyanidins (PAs), the end product of the flavonoid biosynthetic pathway, which are mainly deposited in the innermost cell layer of the testa (chalaza, micropyle and endothelium) (Debeaujon et al, 2003;Dixon, Xie & Sharma, 2005;Lepiniec et al, 2006). Different results of many studies on the seed coat color of Brassica species showed that seed coat color was controlled by different transcription factors and structural genes, such as TT10 (Fu et al, 2007), TT8 (Li et al, 2012), TT2 (Zhou et al, 2016), TT6 (Huang et al, 2016), TT1 (Wang et al, 2016) and TTG1 (Ren et al, 2017).…”