Abstract
BackgroundNoni (Morinda citrifolia Linn.) is a tropical tree that bears climacteric fruit. Previous observations and research have shown that the second day (2 d) after harvest is the most important demarcation point when the fruit has the same appearance as the freshly picked fruit (0 d); however, they are beginning to become water spot appearance. We performed a conjoint analysis of metabolome and transcriptome data for noni fruit of 0 d and 2 d to reveal what happened to the fruit at the molecular level. Genes and metabolites were annotated to KEGG pathways and the co-annotated KEGG pathways were used as a statistical analysis.ResultsWe found 25 pathways that were significantly altered at both metabolic and transcriptional levels, including a total of 285 differentially expressed genes (DEGs) and 11 differential metabolites through an integrative analysis of transcriptomics and metabolomics. The energy metabolism and pathways originating from phenylalanine were disturbed the most. The upregulated resistance metabolites and genes implied the increase of resistance and energy consumption in the postharvest noni fruit. Most genes involved in glycolysis were downregulated, further limiting the available energy. This lack of energy led noni fruit to water spot appearance, a prelude to softening. The metabolites and genes related to the resistance and energy interacted and restricted each other to keep noni fruit seemingly hard within two days after harvest, but actually the softening was already unstoppable.ConclusionsThis study provides a new insight into the relationship between the metabolites and genes of noni fruit, as well as a foundation for further clarification of the post-ripening mechanism in noni fruit.
Highlights
Noni (Morinda citrifolia Linn.) is a tropical tree that bears climacteric fruit
Our results showed the genes of Phenylalanine ammonia-lyase (PAL), Caffeic acid 3-O-methyltransferase (COMT), Cinnamyl alcohol dehydrogenase (CAD), and POX were changed a lot in phenylalanine metabolism, for example, PAL upregulated by 29.63fold and POX upregulated by 7.29-fold (Table 2), indicating the pathway was disturbed most
A hypothesis model was proposed by the conjoint analysis of transcriptomic and metabolomic profiles in noni fruit on the second day vs. the initial day of harvesting (Fig. 6)
Summary
Noni (Morinda citrifolia Linn.) is a tropical tree that bears climacteric fruit. Morinda citrifolia Linn., known as noni as well, is a perennial shrub or tree widely distributed in tropical and subtropical regions [1]. It originated from the Southern Pacific Ocean, such as Polynesian, Marquesas, and Hawaiian, and has been used traditionally in folk medicine for more than 2000 years [2]. More and more studies have provided information on phytochemical compositions of noni fruit, finding variations according to regions, picking time, storage life, and processing methods [8]. It is of great significance to study the softening mechanism of noni fruit after harvest
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