Two diploid woodland strawberry (Fragaria vesca) inbred lines, Ruegen F7-4 (red fruit-bearing) and
YW5AF7 (yellow fruit-bearing) were used to study the regulation of anthocyanin biosynthesis in fruit.
Ruegen F7-4 fruit had similar total phenolics and anthocyanin contents to commercial octoploid
(F. ananassa) cultivar Seascape, while YW5AF7 exhibited relatively low total phenolics content and no
anthocyanin accumulation. Foliar spray of CaCl2 boosted fruit total phenolics content, especially anthocyanins,
by more than 20% in both Seascape and RF7-4. Expression levels of almost all the flavonoid
pathway genes were comparable in Ruegen F7-4 and YW5AF7 green-stage fruit. However, at the turning
and ripe stages, key anthocyanin structural genes, including flavanone 3-hydroxylase (F3H1), dihydroflavonol
4-reductase (DFR2), anthocyanidin synthase (ANS1), and UDP-glucosyltransferase (UGT1), were
highly expressed in Ruegen F7-4 compared with YW5AF7 fruit. Calcium treatment further stimulated the
expression of those genes in Ruegen F7-4 fruit. Anthocyanins isolated from petioles of YW5AF7 and
Ruegen F-7 had the same HPLCeDAD profile, which differed from that of Ruegen F-7 fruit anthocyanins.
All the anthocyanin structural genes except FvUGT1 were detected in petioles of YW5AF7 and Ruegen F-7.
Taken together, these results indicate that the “yellow” gene in YW5AF7 is a fruit specific regulatory
gene(s) for anthocyanin biosynthesis. Calcium can enhance accumulation of anthocyanins and total
phenolics in fruit possibly via upregulation of anthocyanin structural genes. Our results also suggest that
the anthocyanin biosynthesis machinery in petioles is different from that in fruit.