A wild 'albino' bilberry (Vaccinium myrtillus L.) from Slovenia shows three bottlenecks in the anthocyanin pathway and significant differences in the expression of several regulatory genes compared to the common blue berry type.

Zala Zorenc,Darinka Koron,Robert Veberic,Christian Haselmair-Gosch,Ana Slatnar,Silvija Miosic,Heidi Halbwirth,Ming-Hui Chen,Maja Mikulic-Petkovsek,Sara Amancio

doi:10.1371/journal.pone.0190246

Zala Zorenc, Darinka Koron + Show 8 more

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https://doi.org/10.1371/journal.pone.0190246

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Abstract

Relative expressions of structural genes and a number of transcription factors of the anthocyanin pathway relevant in Vaccinium species, and related key enzyme activities were compared with the composition and content of metabolites in skins of ripe fruits of wild albino and blue bilberry (Vaccinium myrtillus) found in Slovenia. Compared to the common blue type, the albino variant had a 151-fold lower total anthocyanin and a 7-fold lower total phenolic content in their berry skin, which correlated with lower gene expression of flavonoid 3-O-glycosyltransferase (FGT; 33-fold), flavanone 3-hydroxylase (FHT; 18-fold), anthocyanidin synthase (ANS; 11-fold), chalcone synthase (CHS, 7.6-fold) and MYBPA1 transcription factor (22-fold). The expression of chalcone isomerase (CHI), dihydroflavonol 4-reductase (DFR), leucoanthocyanidin reductase (LAR), anthocyanidin reductase (ANR) and MYBC2 transcription factor was reduced only by a factor of 1.5–2 in the albino berry skins, while MYBR3 and flavonoid 3’,5’-hydroxylase (F3’5’H) were increased to a similar extent. Expression of the SQUAMOSA class transcription factor TDR4, in contrast, was independent of the color type and does therefore not seem to be correlated with anthocyanin formation in this variant. At the level of enzymes, significantly lower FHT and DFR activities, but not of phenylalanine ammonia-lyase (PAL) and CHS/CHI, were observed in the fruit skins of albino bilberries. A strong increase in relative hydroxycinnamic acid derivative concentrations indicates the presence of an additional bottleneck in the general phenylpropanoid pathway at a so far unknown step between PAL and CHS.

Highlights

Bilberry (Vaccinium myrtillus L.) is a well-known deciduous dwarf shrub growing mostly in cool temperate regions and mountain areas of Europe and Asia
The relative expression of the structural genes chalcone synthase (CHS), chalcone isomerase (CHI), FHT, F3’5’H, dihydroflavonol 4-reductase (DFR), leucoanthocyanidin reductase (LAR), anthocyanidin reductase (ANR), anthocyanidin synthase (ANS) and flavonoid 3-Oglycosyltransferase (FGT) of the flavonoid pathway and of four transcription factors previously described as influencing anthocyanin accumulation in Vaccinium was determined in the blue and albino bilberry skins (Figs 1 and 2)
In this study we characterized for the first time the flavonoid pathway of an albino type of V. myrtillus found in Slovenia [28] by measuring the expression of a range of structural and regulatory genes and selected enzyme activities correlated with the polyphenols accumulated in the berry skins

Summary

Introduction

Bilberry (Vaccinium myrtillus L.) is a well-known deciduous dwarf shrub growing mostly in cool temperate regions and mountain areas of Europe and Asia. R2R3-MYB transcription factors are the key switches for secondary metabolite gene regulation and are important regulators of anthocyanin, proanthocyanidin and flavonol biosynthesis in plants [14] They are known to regulate the expression of chalcone synthase (CHS), flavanone 3-hydroxylase (FHT), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS) and other flavonoid pathway genes in various plant parts (leaves, flowers and fruits) of different horticultural plants such as anthurium [16], apple [17], bog bilberry [18] etc. Mutations of structural and regulatory genes can result in different yellow or white anthocyanin-free phenotypes [19, 21] Such color mutants have always been valuable study objects to obtain insights into the regulation of anthocyanins in nature [22]. Previous studies of rare berry colors of other Vaccinium species have provided a detailed insight into the gene expression of structural and regulatory genes of the anthocyanin pathway [18, 23, 24]

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