Brassica napus is an important cash crop broadly grown for the vegetable and oil values.  Yellow-seeded B. napus is preferred by breeders due to its improved oil and protein quality, less pigments and lignin compared with the black-seeded counterpart.  This study compared the differences in flavonoid and fatty acid contents between yellow rapeseed from the progenies of B. napus–Sinapis alba somatic hybrids and the black-seeded counterpart using RNA-seq analysis.  Through HPLC-PDA-ESI(−)/MS² analysis, it was found that phenylpropanoids and flavonoids (i.e., isorhamnetin, epicatechin, kaempferol, and other derivatives) in yellow seed were significantly lower than those in black seed.  The fatty acid (FA) content in yellow rapeseed was higher than that in black rapeseed due to the variation of C16:0, C18:0, C18:1, C18:2, and C18:3 contents.  RNA-seq analysis of seeds at four and five weeks after flowering (WAF) indicated that differentially expressed genes (DEGs) between black and yellow rapeseeds were enriched in flavonoid and FA biosynthesis, including BnTT3, BnTT4, BnTT18, and BnFAD2.  Also, genes related to FA biosynthesis, desaturation and elongation (FAD3, LEC1, FUS3, and LPAT2) in yellow seed were up-regulated compared to those in black seed, while genes involved in beta-oxidation cycle (AIM1 and KAT2) of yellow seed were down-regulated compared to those in black seed.  The DEGs related to the variation of flavonoids, phenylpropanoids, and FAs would help improve the knowledge of yellow seed character in B. napus and promote rapeseed improvement.

This paper reviews research advances in cytogenetics and germplasm innovation in Brassica allopolyploids, particularly oilseed rape (Brassica napus), in China.  Three naturally evolved Brassica allotetraploid species are cytologically stable but tend to preferentially lose several chromosomes from one subgenome when induced by alien chromosome elimination.  A-subgenome is extracted from B. napus, and the ancestral Brassica rapa was restituted after the total loss of C-subgenome chromosomes.  Genome-wide genetic and epigenetic alterations were observed in both natural and synthetic Brassica allotetraploids.  B. napus was subjected to extensive interspecific hybridization with landraces of B. rapa and Brassica juncea, which exhibit abundant phenotype variations, to widen the genetic diversity in breeding and select numerous elite germplasm resources and cultivars; these cultivars include the representative Zhongyou 821, which also parented numerous other varieties.  Novel B. napus genotypes were obtained using Brassica trigenomic hybrids and allohexaploids (2n=54, AABBCC) by combining subgenomes from extant allotetraploids and diploids as bridge.  Alien additions, substitutions, and translocations of the B. napus genome were developed by intergeneric/intertribal sexual and somatic hybridizations with several crucifers.  Furthermore, mitochondrial DNA recombination promoted the production of novel cytoplasmic male sterile lines.  

    DNA methylation, an important epigenetic modification, serves as a key function in the polyploidization of numerous crops. In this study, early generations of resynthesized Brassica napus (F₁, S₁–S₃), ancestral parents B. rapa and B. oleracea were analyzed to characterize their DNA methylation status during polyploidization, applying DNA methylation-sensitive amplification polymorphism (MSAP) and high-performance liquid chromatography methods. In F₁, 53.4% fragments were inherited from both A- and C-genomes. Besides, 5.04 and 8.87% fragments in F₁ were inherited from A- and C- genome, respectively. 5.85 and 0.8% fragments were newly appeared and disappeared in resynthesized B. napus, respectively. 13.1% of these gene sites were identified with methylation changes in F₁, namely, hypermethylation (7.86%) and hypomethylation (5.24%). The lowest methylation status was detected in F₁ (38.7%) compared with in S₁–S₃. In S₃, 40.32% genes were methylated according to MSAP analysis. Sequencing of methylated fragments indicated that genes involved in multiple biological processes were modified, including transcription factors, protein modification, and transporters. Expression ananlysis of DNA methyltransferase 1 and DNA methyltransferase chromomethylase 3 in different materials was consistent to the DNA methylation status. These results can generally facilitate dissection of how DNA methylation contributes to genetic stability and improvement of B. napus during polyploidization.