GSE69137
Identification of genes related to embryonal control of yellow seed coat in B. 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 with pollen effect. Microcopy of transverse sections of the mature seed shows pigment is deposited only in the epidermal cells, the first cell 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 26-day old brown and yellow seeds. It was assembled into 172,238 independent transcripts and 55,637 unigenes by Trinity. A total of 150 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 transcripted in seeds. However transcription of all the orthologs was independent of the embryonal control of seed coat colour. Of all the Trinity-assembled unigenes, 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 the brown counterpart. By KEGG classification, 14 metabolic pathways were enriched significantly. 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 produced 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 26-day embryo of yellow seeds. Pigment indispensable 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 indicate that embryonal control of seed coat colour is related with Phe and Ala metabolism in the embryo of B. napus. Overall design: Examination of 26-day-old seeds of 2 near isogenic lines with distinct seed coat colour.