Identification and characterization of MYB-bHLH-WD40 regulatory complexes controlling proanthocyanidin biosynthesis in strawberry (Fragaria × ananassa) fruits

• Published in: The New phytologist Vol. 197; no. 2; pp. 454 - 467
• Main Authors: Schaart, Jan G., Dubos, Christian, Romero De La Fuente, Irene, Houwelingen, Adèle M. M. L., Vos, Ric C. H., Jonker, Harry H., Xu, Wenjia, Routaboul, Jean‐Marc, Lepiniec, Loïc, Bovy, Arnaud G.
• Format: Journal Article
• Language: English
• Published: England New Phytologist Trust 01-01-2013; Wiley Subscription Services, Inc; Wiley
• Subjects: Anthocyanidin reductase; anthocyanin biosynthesis; Anthocyanins; Arabidopsis Proteins - metabolism; arabidopsis-thaliana; Basic Helix-Loop-Helix Transcription Factors - metabolism; bHLH; Biosynthesis; Bryopsida - metabolism; Cluster Analysis; Clustering; Colour; Crosses, Genetic; domain protein; expression; factor family; flavonoid biosynthesis; Flavonoids; Flavonols - metabolism; Fragaria - genetics; Fragaria - growth & development; Fragaria ananassa; Fruit - genetics; Fruit - growth & development; Fruiting; Fruits; gene encodes; Gene expression regulation; Gene Expression Regulation, Plant; Gene regulation; Genes; Genes, Plant; Genetic Complementation Test; Genotypes; Helix-loop-helix proteins (basic); Homology; Life Sciences; Metabolome - genetics; Metabolomics; Mutation - genetics; MYB; myb domain; negative regulator; Phylogeny; Plant Proteins - genetics; Plant Proteins - metabolism; Plants; Plants, Genetically Modified; Proanthocyanidins; Proanthocyanidins - biosynthesis; Proteins; Protoplasts; Protoplasts - metabolism; r2r3-myb transcription factor; Reductases; Regulator genes; Regulators; Saccharomyces cerevisiae - metabolism; Sequence Homology, Amino Acid; Strawberries; strawberry (Fragaria × ananassa); Transcription; Transcriptional regulatory elements; Transcriptome - genetics; WD40‐repeat; Yeast; Yeasts; yeast‐two‐hybrid; WD40-repeat; flavonoid biosynthesis; MYB; strawberry (Fragaria9ananassa); bHLH; yeast-two-hybrid
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.12017

Strawberry (Fragaria × ananassa) fruits contain high concentrations of flavonoids. In unripe strawberries, the flavonoids are mainly represented by proanthocyanidins (PAs), while in ripe fruits the red-coloured anthocyanins also accumulate. Most of the structural genes leading to PA biosynthesis in strawberry have been characterized, but no information is available on their transcriptional regulation. In Arabidopsis thaliana the expression of the PA biosynthetic genes is specifically induced by a ternary protein complex, composed of AtTT2 (AtMYB123), AtTT8 (AtbHLH042) and AtTTG1 (WD40-repeat protein).
A strategy combining yeast-two-hybrid screening and agglomerative hierarchical clustering of transcriptomic and metabolomic data was undertaken to identify strawberry PA regulators.
Among the candidate genes isolated, four were similar to AtTT2, AtTT8 and AtTTG1 (FaMYB9/FaMYB11, FabHLH3 and FaTTG1, respectively) and two encode putative negative regulators (FaMYB5 and FabHLH3Δ). Interestingly, FaMYB9/FaMYB11, FabHLH3 and FaTTG1 were found to complement the tt2-1, tt8-3 and ttg1-1 transparent testa mutants, respectively. In addition, they interacted in yeast and activated the Arabidopsis BANYULS (anthocyanidin reductase) gene promoter when coexpressed in Physcomitrella patens protoplasts.
Taken together, these results demonstrated that FaMYB9/FaMYB11, FabHLH3 and FaTTG1 are the respective functional homologues of AtTT2, AtTT8 and AtTTG1, providing new tools for modifying PA content and strawberry fruit quality.