The effects of fruit bagging on levels of phenolic compounds and expression by anthocyanin biosynthetic and regulatory genes in red-fleshed apples

• The bagging effect on red-fleshed apples was evaluated for the first time.
• The accumulation of anthocyanin in apple flesh is sensitive to light.
• The molecular mechanism for red pigmentation in apple flesh was analyzed.

Apples with red fruit flesh are desirable for breeding because they contain more health-beneficial compounds. That color trait is also considered more attractive to consumer. To obtain experimental evidence about the molecular mechanism for this pigmentation, we investigated how the practice of bagging fruit might affect levels of phenolic compounds as well as the expression of anthocyanin biosynthetic and regulatory genes. Two red-fleshed varieties from Xinjiang, P.R. China, were studied – ‘Xiahongrou’ and ‘No.1 Hongxun’. HPLC analysis showed that the contents of anthocyanins in both peel and flesh were decreased by bagging, but were increased again when fruits were re-exposed to sunlight. Except for F3H in ‘No.1 Hongxun’, transcription levels for most anthocyanin biosynthetic genes in the flesh were enhanced after bag removal. MYB10 is a key transcriptional factor in the anthocyanin pathway of these two apple varieties, particularly in the flesh. These results suggest that the development of red coloring when bags are removed could be a result of light-induced coordinated expression by MYB10 and anthocyanin biosynthetic genes in red-fleshed apples.

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