Abstract
Purple pericarps of bread wheat (Triticum aestivum L.) are a useful source of dietary anthocyanins. Previous mapping results indicated that the purple pericarp trait is controlled by two complementary genes located on chromosomes 7D and 2A. However, the identity of the genes and the mechanisms by which they regulate the trait are unknown. In this study, two transcription factors were characterised as anthocyanin activators in purple pericarps: TaPpm1 (purple pericarp-MYB 1) and TaPpb1 (purple pericarp-bHLH 1). Three non-functional variants were detected in the coding sequence of TaPpm1 from non-purple seed lines, in which the function of TaPpm1 was destroyed either by insertion-induced frame shifts or truncated peptides. There were six 261-bp tandem repeats in the promoter region of TaPpb1 in the purple-grained varieties, while there was only one repeat unit present in the non-purple varieties. Furthermore, using yeast two-hybrid, dual luciferase, yeast one-hybrid, and transient assays, we were able to demonstrate that the interaction of TaPpm1 and TaPpb1 co-regulates the synthesis of anthocyanin. Overall, our results provide a better understanding of the molecular basis of anthocyanin synthesis in the wheat pericarp and indicate the existence of an integrated regulatory mechanism that controls production.
Highlights
Anthocyanins are a class of plant flavonoid compounds that exist in the flowers, leaves, fruit, and seeds of many plant species.They have attracted widespread interest due to their various biological functions, including playing protective roles against environmental stress and providing beneficial effects on human health (Sarma and Sharma, 1999; Petroni and Tonelli, 2011)
Identification of differentially expressed genes involved in the anthocyanin pathway Anthocyanins were abundant in the pericarp of Heixiaomai 76’ (H76), and they increased with seed development and in response to high light (Fig. 1).Two complementary genes were indicated as controlling the purple pericarp of H76 (Supplementary Table S2).To identify these genes, high-throughput RNA-sequencing was performed to obtain a broad view of DEGs between the purple pericarp samples (H-10p and H-17d) and a non-purple pericarp sample (H-10d) (Fig. 1)
Two genes governing the purple pericarp trait have been mapped on chromosomes 2A and 7D (Tereshchenko et al, 2012), and have been further identified as a bHLH and an MYB gene, respectively (Khlestkina, 2013; Himi and Taketa, 2015)
Summary
Anthocyanins are a class of plant flavonoid compounds that exist in the flowers, leaves, fruit, and seeds of many plant species.They have attracted widespread interest due to their various biological functions, including playing protective roles against environmental stress and providing beneficial effects on human health (Sarma and Sharma, 1999; Petroni and Tonelli, 2011). The anthocyanin biosynthetic pathway has been well characterized and the corresponding genes have been isolated (Winkel-Shirley, 2001). This biosynthesis process is transcriptionally regulated by the MBW complex of R2R3-MYB, bHLH, and WD40 proteins (Koes et al, 2005). WD40 acts as a docking platform involved in facilitating both the interaction of MYB and bHLH and the stabilization of the transcription factor (TF) complex, but it has no intrinsic enzymatic functions (DNA-binding or initiating target genes) (Ramsay and Glover, 2005; Hichri et al, 2010). R2R3-MYB contains two imperfect repeats, R2 and R3, in the N-terminus, and R2R3-MYB is the most common type in regulating anthocyanin synthesis (Nesi et al, 2001).
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