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

Seed coat colour 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 fibre content. In Brassica napus inheritance of seed coat colour 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 pigment is deposited only in the outer layer of seed coat. By Illumina Hiseq 2000 sequencing technology, a total of 12 G clean data, 116x coverage of coding sequences of B. napus, was achieved from seeds 26 days after pollination. 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 the orthologs was independent of the embryonal control of seed coat colour. Only 55 genes were found to be differentially expressed between the brown seeds and yellow mutant. Among them 50 were up-regulated and 5 were down-regulated in the yellow seeds as compared to their brown counterparts. By KEGG classification, 14 metabolic pathways were significantly enriched. Of these, 5 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 embryo of yellow seeds as compared to 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 colour is related with Phe and Ala metabolism in the embryo of B. napus.

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