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Comparative transcriptome analysis of genes involved in anthocyanin biosynthesis in the pink-white and red fruits of Chinese bayberry (Morella rubra)

Lin, Qihua, Zhong, Qiuzhen, Zhang, Zehuang
Scientia horticulturae 2019 v.250 pp. 278-286
Morella rubra, anthocyanins, biochemical pathways, biosynthesis, cluster analysis, color, cultivars, databases, gene expression, gene expression regulation, quantitative polymerase chain reaction, ripening, small fruits, structural genes, transcription factors, transcriptomics, unigenes
Chinese bayberry (Morella rubra Sieb. and Zucc.) is an ideal fruits crop for fruits color research because of the rapid color changes that occur during ripening. Some structural genes and transcription factors involved in the anthocyanin metabolic pathway have been found in the red fruits variety of Chinese bayberry, but the mechanisms of pink-white color formation in Chinese bayberry fruits have not been reported. The red fruits of the Dongkui (DK) cultivar and the pink-white fruits of the Baidongkui (BDK) strain of Chinese bayberry were selected for transcriptome analysis. A total of 119,701 unigenes were obtained, of which 41.43% were annotated in the non-redundant (Nr) protein database. The total number of differentially expressed genes (DEGs) between the breaker fruits (BDK2) and young fruits (BDK1) was 9024, with 4993 upregulated, including DFR1, DFR2, UFGT and MYB1. The total number of DEGs between the ripe fruits (BDK3) and the breaker fruits (BDK2) was 5226, of which 2592 genes were upregulated. We found enhanced expression of structural genes, such as CHS, CHI, F3H, DFR1, DFR2, F3’H, ANS, UFGT and transcription factors such as MYB1, bHLH1. The total number of DEGs between the ripe fruits of DK (DK3) and BDK (BDK3) was only 630, of which 345 genes were upregulated. We observed enhanced expression of CHS, F3H, DFR1, DFR2, F3’H (88.3%), ANS (71.5%), and UFGT (93.0%). Hierarchy cluster analysis showed that DK3 berries were closest to BDK3 berries and furthest from BDK1 berries based on gene expression. We confirmed the results of our transcriptome analysis using quantitative real-time PCR, anthocyanin content analysis, and measurement of CIRG. Together, our results showed that the BDK pink-white fruits were formed by the upregulated expression of anthocyanin biosynthetic genes and regulatory factors. However, the reduced expression of key anthocyanin biosynthetic genes at the late stage of fruits development in BDK3 fruits compared with DK3 fruits resulted in the failure to form red fruits. Our findings shed light on the regulatory mechanisms and metabolic processes during pink-white fruits ripening of Chinese bayberry.