Abstract
Yellow raspberry fruits have reduced anthocyanin contents and offer unique possibility to study the genetics of pigment biosynthesis in this important soft fruit. Anthocyanidin synthase (Ans) catalyzes the conversion of leucoanthocyanidin to anthocyanidin, a key committed step in biosynthesis of anthocyanins. Molecular analysis of the Ans gene enabled to identify an inactive ans allele in a yellow fruit raspberry (“Anne”). A 5 bp insertion in the coding region was identified and designated as ans+5. The insertion creates a premature stop codon resulting in a truncated protein of 264 amino acids, compared to 414 amino acids wild-type ANS protein. This mutation leads to loss of function of the encoded protein that might also result in transcriptional downregulation of Ans gene as a secondary effect, i.e., nonsense-mediated mRNA decay. Further, this mutation results in loss of visible and detectable anthocyanin pigments. Functional characterization of raspberry Ans/ans alleles via complementation experiments in the Arabidopsis thaliana ldox mutant supports the inactivity of encoded protein through ans+5 and explains the proposed block in the anthocyanin biosynthetic pathway in raspberry. Taken together, our data shows that the mutation inside Ans gene in raspberry is responsible for yellow fruit phenotypes.
Highlights
Fruit pigmentation in raspberries (Rubus idaeus L., Rosaceae) is a complex phenomenon and one of the most important traits for breeding and consumer choice where a range of color patterns from deep purple to yellow exists
flavanone 3β-hydroxylase (F3h), dihydroflavonol 4-reductase (Dfr), and Ufgt genes are upregulated from stage 3 to 4 at different levels in both varieties
In fruits of red variety “Tulameen” the apparent RNA accumulation of Anthocyanidin synthase (Ans) gene is coordinated with the other biosynthetic genes examined (Chs, F3h, Dfr, Ufgt) as it shows a dramatic increase from stage 3 to 4
Summary
Fruit pigmentation in raspberries (Rubus idaeus L., Rosaceae) is a complex phenomenon and one of the most important traits for breeding and consumer choice where a range of color patterns from deep purple to yellow exists. Anthocyanins are water soluble polyphenolic pigments responsible for the colors of many flowers (Chung et al, 2010; Luo et al, 2015; Sundaramoorthy et al, 2016), fruits (Saito et al, 1999; Debes et al, 2011; Liu et al, 2013; Ben-Simhon et al, 2015), and other plant tissues (Gould et al, 2000; Kim et al, 2004; Zhou et al, 2010) Their biochemical role in plants is not fully understood, they have been considered to protect tissues from biotic and abiotic stresses, delay in senescence, assist in photosynthetic machinery, delay over-ripening and increase shelf-life of fruits and act as ANS Rubus scavengers of reactive oxygen intermediates (Zhang et al, 2013, 2016; Landi et al, 2015; Yousuf et al, 2016). Aside from the health benefits, anthocyanins play an important role as an indicator of fruit quality and consumer acceptance (Espín et al, 2007)
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