A knockout mutation in the lignin biosynthesis gene CCR1 explains a major QTL for acid detergent lignin content in Brassica napus seeds |
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Authors: | Liezhao Liu Anna Stein Benjamin Wittkop Pouya Sarvari Jiana Li Xingying Yan Felix Dreyer Martin Frauen Wolfgang Friedt Rod J Snowdon |
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Institution: | (1) Department of Plant Breeding, IFZ Research Centre for Biosystems, Land Use and Nutrition, Justus Liebig University, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany;(2) College of Agronomy and Biotechnology, Southwest University, Beibei, Chongqing, 400716, China;(3) Norddeutsche Pflanzenzucht Hans-Georg Lembke KG, 24363 Hohenlieth, Germany |
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Abstract: | Seed coat phenolic compounds represent important antinutritive fibre components that cause a considerable reduction in value
of seed meals from oilseed rape (Brassica napus). The nutritionally most important fibre compound is acid detergent lignin (ADL), to which a significant contribution is
made by phenylpropanoid-derived lignin precursors. In this study, we used bulked-segregant analysis in a population of recombinant
inbred lines (RILs) from a cross of the Chinese oilseed rape lines GH06 (yellow seed, low ADL) and P174 (black seed, high
ADL) to identify markers with tight linkage to a major quantitative trait locus (QTL) for seed ADL content. Fine mapping of
the QTL was performed in a backcross population comprising 872 BC1F2 plants from a cross of an F7 RIL from the above-mentioned population, which was heterozygous for this major QTL and P174. A 3:1 phenotypic segregation
for seed ADL content indicated that a single, dominant, major locus causes a substantial reduction in ADL. This locus was
successively narrowed to 0.75 cM using in silico markers derived from a homologous Brassica rapa sequence contig spanning the QTL. Subsequently, we located a B. rapa orthologue of the key lignin biosynthesis gene CINNAMOYL CO-A REDUCTASE 1 (CCR1) only 600 kbp (0.75 cM) upstream of the nearest linked marker. Sequencing of PCR amplicons, covering the full-length coding
sequences of Bna.CCR1 homologues, revealed a locus in P174 whose sequence corresponds to the Brassica oleracea wild-type allele from chromosome C8. In GH06, however, this allele is replaced by a homologue derived from chromosome A9
that contains a loss-of-function frameshift mutation in exon 1. Genetic and physical map data infer that this loss-of-function
allele has replaced a functional Bna.CCR1 locus on chromosome C8 in GH06 by homoeologous non-reciprocal translocation. |
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