Increased accumulation of anthocyanins in Fragaria chiloensis fruits by transient suppression of FcMYB1 gene

Transient transformation of strawberry fruit was analyzed focusing on accumulation of anthocyanins. Lower FcMYB1 transcript level was related with a more pigmented phenotype and changes in both transcriptional profiles of structural genes of flavonoid pathway and flavonoid compounds. [Display omitted] ► FcMYB1, ortholog of FaMYB1 (a suppressor of flavonoid biosynthesis) was cloned from white strawberry Fragaria chiloensis. ► Expression of FcMYB1 was higher in white strawberry than in red strawberry during fruit development. ► RNAi silencing construct depleted FcMYB1 mRNA levels in white strawberry fruits, enhancing their pigmentation. ► Fruits with lower transcript levels of this TF showed increased contents of anthocyanin and decreased levels of flavan 3-ols. Anthocyanins and proanthocyanidins (PAs), flavonoid-derived metabolites with different physiological roles, are produced by plants in a coordinated manner during fruit development by the action of transcription factors (TFs). These regulatory proteins have either an activating or repressing effect over structural genes from the biosynthetic pathway under their control. FaMYB1, a TF belonging to the R2R3-MYB family and isolated from commercial strawberry fruit (Fragaria×ananassa), was reported as a transcriptional repressor and its heterologous over-expression in tobacco flowers suppressed flavonoid-derived compound accumulation. FcMYB1, an ortholog of FaMYB1 isolated from the white Chilean strawberry (Fragaria chiloensis ssp. chiloensis f. chiloensis), showed higher transcript levels in white (F. chiloensis) than in red (F.×ananassa cv. Camarosa) fruits. In order to assess its contribution to the discolored phenotype in F. chiloensis, FcMYB1 was transiently down-regulated in planta using an RNAi-based approach. Quantitative real-time PCR on FcMYB1 down-regulated fruits resulted an up-regulation of anthocyanidin synthase (ANS) and a strong repression of anthocyanidin reductase (ANR) and leucoanthocyanidin reductase (LAR) transcript accumulation. In addition, these fruits showed increased concentrations of anthocyanins and undetectable levels of flavan 3-ols. Altogether, these results indicate a role for FcMYB1 in regulation of the branching-point of the anthocyanin/PA biosynthesis determining the discolored phenotype of the white Chilean strawberry fruit.