Abstract
Yellow-seed (i.e., yellow seed coat) is one of the most important agronomic traits of Brassica plants, which is correlated with seed oil and meal qualities. Previous studies on the Brassicaceae, including Arabidopsis and Brassica species, proposed that the seed-color trait is correlative to flavonoid and lignin biosynthesis, at the molecular level. In Arabidopsis thaliana, the oxidative polymerization of flavonoid and biosynthesis of lignin has been demonstrated to be catalyzed by laccase 15, a functional enzyme encoded by the AtTT10 gene. In this study, eight Brassica TT10 genes (three from B. napus, three from B. rapa and two from B. oleracea) were isolated and their roles in flavonoid oxidation/polymerization and lignin biosynthesis were investigated. Based on our phylogenetic analysis, these genes could be divided into two groups with obvious structural and functional differentiation. Expression studies showed that Brassica TT10 genes are active in developing seeds, but with differential expression patterns in yellow- and black-seeded near-isogenic lines. For functional analyses, three black-seeded B. napus cultivars were chosen for transgenic studies. Transgenic B. napus plants expressing antisense TT10 constructs exhibited retarded pigmentation in the seed coat. Chemical composition analysis revealed increased levels of soluble proanthocyanidins, and decreased extractable lignin in the seed coats of these transgenic plants compared with that of the controls. These findings indicate a role for the Brassica TT10 genes in proanthocyanidin polymerization and lignin biosynthesis, as well as seed coat pigmentation in B. napus.
Highlights
Brassica species belong to the same taxonomic family Brassicaceae as Arabidopsis, representing the closest relatives to Arabidopsis thaliana
Three full-length cDNAs, designated as BnTT10-1, BnTT10-2 and BnTT10-3, were cloned from B. napus (Fig. S1), two full-length cDNAs BoTT10-1, BoTT10-1pse were isolated from B. oleracea, and three full-length cDNAs BrTT10-1A, BrTT10-2, BrTT10-1B were obtained from B. rapa (Table S2)
Our results of gene cloning and Southern blot hybridization suggest that the eight cloned Brassica TT10 genes comprise the majority of TT10 genes in B. napus and its two parental species
Summary
Brassica species belong to the same taxonomic family Brassicaceae as Arabidopsis, representing the closest relatives to Arabidopsis thaliana. The genus Brassica contains many oilseed, vegetable and ornamental crops that are important sources of cooking oil, vegetables, and protein-rich meal for livestock feed. Among these species, Brassica napus is one of the most important oilseed crops cultivated, worldwide. Extensive studies have established that the B. napus yellow-seed trait is highly correlated with high oil and meal qualities [1,2,3]. Currently, seed stock for the natural B. napus yellow-seeded genotype is unavailable. A lack of information concerning the molecular basis controlling yellowseed trait inheritance has seriously hampered progress in the breeding of yellow-seeded genotypes
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