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Abstract
Flavonoids belong to the family of polyphenolic secondary metabolites and contribute to fruit quality traits. It has been shown that MBW complexes (MYB-bHLH-WD40) regulate the flavonoids biosynthesis in different plants, but only a limited number of MBW complexes have been identified in strawberry species in general. In this study, we identified 112 R2R3-MYB proteins in woodland strawberry; 12 of them were found to have potential functions in regulating flavonoids biosynthesis by phylogenetic analysis. qRT-PCR assays showed that FvMYB3, FvMYB9, FvMYB11, FvMYB22, FvMYB64, and FvMYB105 mostly expressed at green stage of fruit development, aligned with proanthocyanidins accumulation; FvMYB10 and FvMYB41 showed higher expression levels at turning and ripe stages, aligned with anthocyanins accumulation. These results suggest that different MYBs might be involved in flavonoids biosynthesis at specific stages. Furthermore, FvMYB proteins were demonstrated to interact with FvbHLH proteins and induce expression from the promoters of CHS2 and DFR2 genes, which encode key enzymes in flavonoids biosynthesis. The co-expression of FvMYB and FvbHLH proteins in strawberry fruits also promoted the accumulation of proanthocyanidins. These findings confirmed and provided insights into the biofunction of MBW components in the regulation of flavonoid biosynthesis in woodland strawberry.
Highlights
Strawberry is favored by consumers mainly because of its unique aroma, sweet taste, bright color and nutritional value
In order to identify R2R3-MYB genes in strawberry, the HMM profile (Pfam:00249) of MYB DNA-binding domain was used to blast against the woodland strawberry genome database (F. vesca Whole Genome v4.0.a2) from GDR
We studied the transcript levels of MYBs and bHLHs, and their effects on the accumulation of flavonoids in strawberry fruits at five stages of fruit development, including green stage, white stage, pre-turning stage, turning stage and ripe stage. qRT-PCR results showed that the transcript level of a bHLH gene (FvMYC1) and nine MYB genes (FvMYB3, FvMYB9, FvMYB11, FvMYB21, FvMYB22, FvMYB45, FvMYB64, FvMYB77, and FvMYB105) was higher at green stage, but significantly decreased at the other four stages (Figure 2 and Supplementary Figure 3), matching proanthocyanidins biosynthesis pattern, which accumulated mainly at the early stages, especially at the green stage (Figure 3A)
Summary
Strawberry is favored by consumers mainly because of its unique aroma, sweet taste, bright color and nutritional value. These quality traits are largely determined by the secondary metabolites in the fruit. Flavonoids give plants their attractive colors for pollen and seed dispersal, and protect plants against ultraviolet radiation (Winkel-Shirley, 2001; Emiliani et al, 2013). Flavonoids may act as antioxidants or signaling molecules to exert potential beneficial effects on human health (He and Giusti, 2010), as well as being antimicrobial agents in plant-microbe interactions and plant defense response (Nijveldt et al, 2001; Battino et al, 2009).
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