Abstract
Anthocyanins are important health-promoting phytochemicals that are abundant in many fleshy fruits. Bilberry (Vaccinium myrtillus) is one of the best sources of these compounds. Here, we report on the expression pattern and functional analysis of a SQUAMOSA-class MADS box transcription factor, VmTDR4, associated with anthocyanin biosynthesis in bilberry. Levels of VmTDR4 expression were spatially and temporally linked with color development and anthocyanin-related gene expression. Virus-induced gene silencing was used to suppress VmTDR4 expression in bilberry, resulting in substantial reduction in anthocyanin levels in fully ripe fruits. Chalcone synthase was used as a positive control in the virus-induced gene silencing experiments. Additionally, in sectors of fruit tissue in which the expression of the VmTDR4 gene was silenced, the expression of R2R3 MYB family transcription factors related to the biosynthesis of flavonoids was also altered. We conclude that VmTDR4 plays an important role in the accumulation of anthocyanins during normal ripening in bilberry, probably through direct or indirect control of transcription factors belonging to the R2R3 MYB family.
Highlights
Anthocyanins are important health-promoting phytochemicals that are abundant in many fleshy fruits
The full-length VmTDR4 cDNA is related by sequence homology to FRUITFULL gene (FUL) from Arabidopsis and TDR4/FULlike genes from tomato; VmTDR4 showed 72% identity to tomato TDR4 at the nucleotide level and 70% identity at the amino acid level
Some of the key genes involved in the molecular regulation of fruit ripening have been revealed through the study of nonripening mutants in tomato, such as rin, Colorless non-ripening (Cnr), Nr, and nor (Giovannoni, 2007; Seymour et al, 2008)
Summary
Anthocyanins are important health-promoting phytochemicals that are abundant in many fleshy fruits. The biosynthetic pathway in plants leading to anthocyanins is well established, and transcription factors that directly regulate multiple steps of the expression of genes in this metabolic pathway are known (Grotewold, 2006) This information has recently been used to generate tomatoes (Solanum lycopersicum) containing. SQUA MADS box genes are commonly associated with floral development and especially the regulation of floral meristem identity (Simpson et al, 1999; Theissen, 2001; Scott et al, 2002) This class of transcription factors has been shown, to have other functions. LeMADS-RIN and LeSBP-CNR are necessary for normal ripening in tomato, with the latter likely controlling the expression of the SQUA gene TDR4. These genes and other related transcription factors can be seen as part of the highlevel regulatory network controlling the ripening process. Their links to downstream effectors that bring about changes in color, texture, and flavor, are poorly understood
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