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Targeted mutagenesis of BnTT8 homologs controls yellow seed coat development for effective oil production in Brassica napus L.

ABSTRACT: Yellow seed is a desirable trait with great potential for improving seed quality in Brassica crops. Unfortunately, no natural or induced yellow seed germplasms have been found in Brassica napus, an important oil crop, which likely reflects its genome complexity and the difficulty of the simultaneous random mutagenesis of multiple gene copies with functional redundancy. Here, we demonstrate the first application of CRISPR/Cas9 for creating yellow-seeded mutants in rapeseed. The targeted mutations of the BnTT8 gene were stably transmitted to successive generations, and a range of homozygous mutants with loss-of-function alleles of the target genes were obtained for phenotyping. The yellow-seeded phenotype could be recovered only in targeted mutants of both BnTT8 functional copies, indicating that the redundant roles of BnA09.TT8 and BnC09.TT8b are vital for seed colour. The BnTT8 double mutants produced seeds with elevated seed oil and protein content and altered fatty acid (FA) composition without any serious defects in the yield-related traits, making it a valuable resource for rapeseed breeding programmes. Chemical staining and histological analysis showed that the targeted mutations of BnTT8 completely blocked the proanthocyanidin (PA)-specific deposition in the seed coat. Further, transcriptomic profiling revealed that the targeted mutations of BnTT8 resulted in the broad suppression of phenylpropanoid/flavonoid biosynthesis genes, which indicated a much more complex molecular mechanism underlying seed colour formation in rapeseed than in Arabidopsis and other Brassica species. In addition, gene expression analysis revealed the possible mechanism through which BnTT8 altered the oil content and fatty acid composition in seeds.

SUBMITTER: Zhai Y

PROVIDER: S-EPMC7152602 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature

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Targeted mutagenesis of BnTT8 homologs controls yellow seed coat development for effective oil production in Brassica napus L.

Zhai Yungu Y Yu Kaidi K Cai Shengli S Hu Limin L Hu Limin L Amoo Olalekan O Xu Lei L Yang Yang Y Ma Boyuan B Jiao Yangmiao Y Zhang Chaofeng C Khan Muhammad Hafeez Ullah MHU Khan Shahid Ullah SU Fan Chuchuan C Zhou Yongming Y

Plant biotechnology journal 20191111 5

Yellow seed is a desirable trait with great potential for improving seed quality in Brassica crops. Unfortunately, no natural or induced yellow seed germplasms have been found in Brassica napus, an important oil crop, which likely reflects its genome complexity and the difficulty of the simultaneous random mutagenesis of multiple gene copies with functional redundancy. Here, we demonstrate the first application of CRISPR/Cas9 for creating yellow-seeded mutants in rapeseed. The targeted mutations ...[more]

PMID: 31637846

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Project description: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.

Project description: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.

Dataset Information

Targeted mutagenesis of BnTT8 homologs controls yellow seed coat development for effective oil production in Brassica napus L.

Publications

Targeted mutagenesis of BnTT8 homologs controls yellow seed coat development for effective oil production in Brassica napus L.

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