Integrative transcriptomic and metabolomic analyses reveal the mechanisms behind acidity differences in the pulp of fresh longan cv. ‘Fuyan’ and ‘Dongbi’ during storage

Abstract

To understand the underlying mechanism of the organic acid accumulation of postharvest longan fruit, integrative analyses of transcriptome and metabolome were performed in the fruit of two longan varieties (‘Fuyan’ and ‘Dongbi’) with different storability. Compared with ‘Dongbi’ longan, the ‘Fuyan’ cultivar exhibited higher fruit respiration rate, pulp breakdown index, and TA content, but a lower TSS content during storage. Targeted metabolomic analysis revealed that, in comparison to ‘Dongbi’ longan, during storage, ‘Fuyan’ longan accumulated higher levels of four organic acids, including 3-phenyllactic acid, lactate, succinic acid, and oxaloacetate. Transcriptomic analysis showed that DEGs between ‘Fuyan’ and ‘Dongbi’ longans were primarily enriched in respiration metabolism pathways, including glycolysis, gluconeogenesis, and the TCA cycle. Additionally, WGCNA identified hub genes involved in these metabolic pathways. RT-qPCR analysis indicated that the expression of related genes (DlLDH, DlACL, DlPEPC, DlMDH, DlAST and DlSCS) was upregulated in ‘Fuyan’ longan compared with ‘Dongbi’ longan during storage. These findings suggest that the increase in longan pulp acidity is attributed to organic acid accumulation and an enhanced respiration metabolism, resulting in the poor storability of ‘Fuyan’ longan during storage.