Abstract
A comprehensive investigation of abscisic acid (ABA) biosynthesis and its influence on other important phytochemicals is critical for understanding the versatile roles that ABA plays during strawberry fruit ripening. Using RNA-seq technology, we sampled strawberry fruit in response to ABA or nordihydroguaiaretic acid (NDGA; an ABA biosynthesis blocker) treatment during ripening and assessed the expression changes of genes involved in the metabolism of pigments, ascorbic acid (AsA) and folic acid in the receptacles. The transcriptome analysis identified a lot of genes differentially expressed in response to ABA or NDGA treatment. In particular, genes in the anthocyanin biosynthesis pathway were actively regulated by ABA, with the exception of the gene encoding cinnamate 4-hydroxylase. Chlorophyll degradation was accelerated by ABA mainly owing to the higher expression of gene encoding pheide a oxygenase. The decrease of β-carotene content was accelerated by ABA treatment and delayed by NDGA. A high negative correlation rate was found between ABA and β-carotene content, indicating the importance of the requirement for ABA synthesis during fruit ripening. In addition, evaluation on the folate biosynthetic pathway indicate that ABA might have minor function in this nutrient’s biosynthesis process, however, it might be involved in its homeostasis. Surprisingly, though AsA content accumulated during fruit ripening, expressions of genes involved in its biosynthesis in the receptacles were significantly lower in ABA-treated fruits. This transcriptome analysis expands our understanding of ABA’s role in phytochemical metabolism during strawberry fruit ripening and the regulatory mechanisms of ABA on these pathways were discussed. Our study provides a wealth of genetic information in the metabolism pathways and may be helpful for molecular manipulation in the future.
Highlights
The strawberry is one of the favorite fruits throughout the world and may be classified as a functional food as it is a rich source of phytochemicals and vitamins, both of which have relevant biological activities in human health [1,2]
A similar pattern was observed in another important colored phytochemical, chlorophyll, which degraded while anthocyanins accumulated (Fig 2D)
Until day 8, the ascorbic acid (AsA) content in Abscisic acid (ABA)- and nordihydroguaiaretic acid (NDGA)-treated receptacles was 1.6-fold and 80% of that in the control samples (Fig 2F). These results indicate that ABA may have a regulatory role in the metabolism of many phytochemicals during strawberry fruit ripening, but it has a minor influence on folate biosynthesis
Summary
The strawberry is one of the favorite fruits throughout the world and may be classified as a functional food as it is a rich source of phytochemicals and vitamins, both of which have relevant biological activities in human health [1,2]. It is known that the carotenoid content is very low in strawberry fruit; previous studies [5,7] reported that the ABA concentration in the strawberry fruit is similar to that of the tomato fruit, a fruit typically rich in carotenoids. This suggests that carotenoids may be mainly used to synthesize ABA in strawberry fruit. Because ABA plays important roles in many physiological processes, an investigation of ABA biosynthesis may facilitate our understanding of its functions in the regulation of strawberry fruit ripening
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