Abstract
Yellow seeds are a favorable trait for Brassica crops breeding due to better quality than their black-seeded counterparts. Here, we compared the Brassica napus seed coat transcriptomes between yellow- and brown-seeded near-isogenic lines (Y-NIL and B-NIL) that were developed from the resynthesized yellow-seeded line No. 2127-17. A total of 4,974 differentially expressed genes (DEG) were identified during seed development, involving 3,128 up-regulated and 1,835 down-regulated genes in yellow seed coats. Phenylpropanoid and flavonoid biosynthesis pathways were enriched in down-regulated genes, whereas the top two pathways for up-regulated genes were plant–pathogen interaction and plant hormone signal transduction. Twelve biosynthetic genes and three regulatory genes involved in the flavonoid pathway exhibited similar expression patterns in seed coats during seed development, of which the down-regulation mainly contributed to the reduction of proanthocyanidins (PAs) in yellow seed coats, indicating that these genes associated with PA biosynthesis may be regulated by an unreported common regulator, possibly corresponding to the candidate for the dominant black-seeded gene D in the NILs. Three transcription factor (TF) genes, including one bHLH gene and two MYB-related genes that are located within the previous seed coat color quantitative trait locus (QTL) region on chromosome A09, also showed similar developmental expression patterns to the key PA biosynthetic genes and they might thus potentially involved participate in flavonoid biosynthesis regulation. Our study identified novel potential TFs involved in PAs accumulation and will provide pivotal information for identifying the candidate genes for seed coat color in B. napus.
Highlights
Brassica napus is one of the most important oilseed crops across the world which provides vegetable oils and biofuels for human life and high-quality proteins for livestock feed
No differences were observed in the undamaged seeds or embryos of the four lines before or after staining (Supplementary Figure 1), indicating the differences in PAs between black/brown and yellow seeds distinctively occurred in the inner endothelium. These results are similar to previous studies that showed that PA content differs between black/brown and yellow seed coats of B. napus and A. thaliana (Dixon et al, 2005; Auger et al, 2010; Jiang et al, 2013; Qu et al, 2013)
To identify the candidate genes for the D locus, we investigated the transcriptomes of the yellow and brown seed coats in the pair of B. napus near-isogenic lines (NILs), which carried the major quantitative trait locus (QTL) Bnsc-9a
Summary
Brassica napus is one of the most important oilseed crops across the world which provides vegetable oils and biofuels for human life and high-quality proteins for livestock feed. Breeding B. napus cultivars with yellow seed coats is a desirable method for improving the oil content and meal quality of rapeseed, because yellow seeds have a number of advantages that include a thinner. PAs are synthesized as one of end products of the flavonoid biosynthesis pathway (Figure 1), which has been well described in some reviews (Lepiniec et al, 2006; Saito et al, 2013; Appelhagen et al, 2014; Xu et al, 2014). More than 27 genes have been identified to participate in or affect flavonoid biosynthesis, mainly including biosynthetic and regulatory genes. Anthocyanin biosynthesis is regulated by different MBW complexes comprised of PRODUCTION OF
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