Embryonal Control of Yellow Seed Coat Locus ECY1 Is Related to Alanine and Phenylalanine Metabolism in the Seed Embryo of Brassica napus

Abstract

Seed coat color is determined by the type of pigment deposited in the seed coat cells. It is related to important agronomic traits of seeds such as seed dormancy, longevity, oil content, protein content and fiber content. In Brassica napus, inheritance of seed coat color is related to maternal effects and pollen effects (xenia effects). In this research we isolated a mutation of yellow seeded B. napus controlled by a single Mendelian locus, which is named Embryonal Control of Yellow seed coat 1 (Ecy1). Microscopy of transverse sections of the mature seed show that pigment is deposited only in the outer layer of the seed coat. Using Illumina Hisequation 2000 sequencing technology, a total of 12 GB clean data, 116× coverage of coding sequences of B. napus, was achieved from seeds 26 d after pollination (DAP). It was assembled into 172,238 independent transcripts, and 55,637 unigenes. A total of 139 orthologous genes of Arabidopsis transparent testa (TT) genes were mapped in silico to 19 chromosomes of B. napus. Only 49 of the TT orthologous genes are transcribed in seeds. However transcription of all orthologs was independent of embryonal control of seed coat color. Only 55 genes were found to be differentially expressed between brown seeds and the yellow mutant. Of these 55, 50 were upregulated and five were downregulated in yellow seeds as compared to their brown counterparts. By KEGG classification, 14 metabolic pathways were significantly enriched. Of these, five pathways: phenylpropanoid biosynthesis, cyanoamino acid metabolism, plant hormone signal transduction, metabolic pathways, and biosynthesis of secondary metabolites, were related with seed coat pigmentation. Free amino acid quantification showed that Ala and Phe were present at higher levels in the embryos of yellow seeds as compared to those of brown seeds. This increase was not observed in the seed coat. Moreover, the excess amount of free Ala was exactly twice that of Phe in the embryo. The pigment substrate chalcone is synthesized from two molecules of Ala and one molecule of Phe. The correlation between accumulation of Ala and Phe, and disappearance of pigment in the yellow seeded mutant, suggests that embryonal control of seed coat color is related with Phe and Ala metabolism in the embryo of B. napus.

TRANSPARENT TESTA 4‐mediated flavonoids negatively affect embryonic fatty acid biosynthesis in Arabidopsis

“…For several decades, yellow‐coloured seeds have been of particular interest to oilseed breeders because of the increased oil content of these seeds, which is considered to be a consequence of thinner seed coats, which contain decreased levels of pigments, melanin, polyphenols, lignin, and crude fiber (Wang et al, ; Yu, ). However, the mechanisms via which pale‐coloured seeds generate high seed FA content are not completely understood.…”

Alanine aminotransferase controls seed dormancy in barley

“…It is known that the hard seed coat of legumes prevents germination by restricting the supply of oxygen in the embryo. The yellow seed coat locus ECY1 in Brassica napus also controls dormancy and has been implicated in alanine metabolism 35 . This is consistent with the use of hydrogen peroxide (H 2 O 2 ) to break dormancy in barley seeds 36 but little is known about the oxygen status of mature barley grain and whether the release of low oxygen levels is an important early event in germination or whether the various isoforms of barley AlaAT play a direct role in breaking dormancy is not clear at this stage.…”

Grain dormancy genes responsible for preventing pre-harvest sprouting in barley and wheat

“…Chalcone is an intermediate metabolite made during the synthesis of proanthocyanidin. Free alanine residues in the embryo are used to make chalcone for pigmentation synthesis in the seed coat of Brassica napus ( Wang et al 2016 ). Thus, different AlaAT genotypes might affect dormancy through regulation of grain color; however, so far, there is no evidence to suggest that AlaAT is involved in the regulation of chalcone biosynthesis in barley.…”