Red Fuji apple (Malus domestica Borkh, cv. ‘Nagafu No. 2’) fruit was used to study the variation of pigment content and the activity of phenylalanine ammonia-lyase (PAL) in the peel and sugar content of apple flesh during growth and development after bag removal. The transcription regulatory factor MYB10d (GenBank Accession Number: GQ183802) was cloned and its expression in fruit was measured at different stages after bag removal. The results showed that total chlorophyll content significantly declined in double-bagged fruit as compared to control fruit, and this effect was more pronounced for chlorophyll a than chlorophyll b. Carotenoid content declined less than the chlorophyll content. Anthocyanin content was noticeably lower than control fruit at bag removal but rapidly rose following removal. The anthocyanin content exceeded the control value on the 6th day following removal and was approximately double the control group on the 8th day after bag removal. The activity of PAL tended to rise and then declined after bag removal in the treated fruit, while that of the control fruit decreased slowly. On the 2nd day after removal, the activity of PAL in treated fruit exceeded the control fruit and reached a maximum on the 6th day after bag removal. The total soluble sugar content was somewhat reduced by bagging. However, the total soluble sugar content (fructose and glucose) increased after bag removal, although, it was lower than the control fruit and showed a significant positive correlation with anthocyanin content. Sucrose content increased rapidly until the 4th day after bag removal and then declined. MYB10d-coded protein, a member of the MYB transcription factor family was related to anthocyanin biosynthesis. Quantitative real time PCR (qRT-PCR) was employed to examine the gene expression levels at different phases after bag removal, and the results indicated that MYB10d expression in treated fruit reached a maximum on the 2nd day after bag removal and declined sharply thereafter. Conversely, MYB10d expression in control fruit remained stable.
Key words: Apple, MYB10d, bag removal.
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