Transcriptome and metabolome analyses of sugar and organic acid metabolism in Ponkan (Citrus reticulata) fruit during fruit maturation

• Published in: Gene 2015-01, Vol.554 (1), p.64-74
• Main Authors: Lin, Qiong, Wang, Chengyang, Dong, Wencheng, Jiang, Qing, Wang, Dengliang, Li, Shaojia, Chen, Ming, Liu, Chunrong, Sun, Chongde, Chen, Kunsong
• Format: Article
• Language: English
• Subjects: Acetyl Coenzyme A - metabolism; Acids - metabolism; Carbohydrate Metabolism; Citrates - metabolism; Citric Acid Cycle; Citrus; Citrus - genetics; Citrus - metabolism; Citrus reticulata; Fruit - growth & development; Fruit - metabolism; gamma-Aminobutyric Acid - metabolism; Gas Chromatography-Mass Spectrometry; Gene Expression Profiling; Gene Expression Regulation, Plant; Genome, Plant; Glycolysis; Metabolism; Metabolome; Organic acid; Ponkan; Sequence Analysis, RNA; Sucrose - metabolism; Sugar; Transcriptome
• ISSN: 0378-1119; 1879-0038
• DOI: 10.1016/j.gene.2014.10.025

Ponkan (Citrus reticulata Blanco cv. Ponkan) is an important mandarin citrus in China. However, the low ratio of sugars to organic acids makes it less acceptable for consumers. In this work, three stages (S120, early development stage; S195, commercial harvest stage; S205, delayed harvest stage) of Ponkan fruit were selected for study. Among 28 primary metabolites analyzed in fruit, sugars increased while organic acids in general decreased. RNA-Seq analysis was carried out and 19,504 genes were matched to the Citrus clementina genome, with 85 up-regulated and 59 down-regulated genes identified during fruit maturation. A sucrose phosphate synthase (SPS) gene was included in the up-regulated group, and this was supported by the transcript ratio distribution. Expression of two asparagine transferases (AST), and a specific ATP-citrate lyase (ACL) and glutamate decarboxylase (GAD) members increased during fruit maturation. It is suggested that SPS, AST, ACL and GAD coordinately contribute to sugar accumulation and organic acid degradation during Ponkan fruit maturation. Both the glycolysis pathway and TCA cycle were accelerated during later maturation, indicating the flux change from sucrose metabolism to organic acid metabolism was enhanced, with citrate degradation occurring mainly through the gamma-aminobutyric acid (GABA) and acetyl-CoA pathways. •RNA-Seq profiled 19,504 genes in Ponkan fruit of different maturation stages.•SPS, AST, ACL and GAD coordinately contributed to sugar accumulation and organic acid degradation.•Citrate degradation occurred through GABA and acetyl-CoA pathways during fruit maturation.•Delayed harvest contributed to better fruit quality.