Abstract
Soluble sugars and organic acids are important components of fruit flavor and have a strong impact on the overall organoleptic quality of watermelon (Citrullus lanatus) fruit. Several studies have analyzed the expression levels of the genes related to soluble sugar accumulation and the dynamic changes in their content during watermelon fruit development and ripening. Nevertheless, to date, there have been no reports on the organic acid content in watermelon or the genes regulating their synthesis. In this study, the soluble sugars and organic acids in watermelon were measured and a comparative transcriptome analysis was performed to identify the key genes involved in the accumulation of these substances during fruit development and ripening. The watermelon cultivar ‘203Z’ and its near-isogenic line (NIL) ‘SW’ (in the ‘203Z’ background) were used as experimental materials. The results suggested that soluble sugar consist of fructose, glucose and sucrose while malic-, citric-, and oxalic acids are the primary organic acids in watermelon fruit. Several differentially expressed genes (DEGs) related to soluble sugar- and organic acid accumulation and metabolism were identified. These include the DEGs encoding raffinose synthase, sucrose synthase (SuSy), sucrose-phosphate synthase (SPSs), insoluble acid invertases (IAI), NAD-dependent malate dehydrogenase (NAD-cyt MDH), aluminum-activated malate transporter (ALMT), and citrate synthase (CS). This is the first report addressing comparative transcriptome analysis via NILs materials in watermelon fruit. These findings provide an important basis for understanding the molecular mechanism that leads to soluble sugar and organic acid accumulation and metabolism during watermelon fruit development and ripening.
Highlights
Watermelon [Citrullus lanatus (Thunb.) Matsum and Nakai] belongs to the Cucurbitaceae and is an important and popular staple summertime fresh fruit worldwide
The maximum glucose content was measured at 18 days after pollination (DAP) (Fig 1C) while that of fructose was detected at 34 DAP (Fig 1D)
The pH of ‘203Z’ and ‘SW’ fruit pulp gradually decreased between 10 DAP and 26 DAP increased slightly at 34 DAP (Fig 1E). In both ‘203Z’ and ‘SW’, the malic- and citric acid content peaked during fruit ripening at 26 DAP decreased at 34 DAP (Fig 1F and 1G)
Summary
Watermelon [Citrullus lanatus (Thunb.) Matsum and Nakai] belongs to the Cucurbitaceae and is an important and popular staple summertime fresh fruit worldwide. It constitutes 7% of the global area dedicated to fruit and vegetable production [1]. Watermelon fruit provides large amounts of water and nutrients including sugars, carotenoids, lycopene, minerals, and amino acids[2, 3]. Comparative transcriptome analysis reveals key genes in watermelon interest Scientific Institution Basal Research Fund
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