Abstract
Abscisic acid (ABA) has been proven to be involved in the regulation of climacteric fruit ripening, but a comprehensive investigation of its influence on ripening related processes is still lacking. By applying the next generation sequencing technology, we conducted a comparative analysis of the effects of exogenous ABA and NDGA (Nordihydroguaiaretic acid, an inhibitor of ABA biosynthesis) on tomato fruit ripening. The high throughput sequencing results showed that out of the 25728 genes expressed across all three samples, 10388 were identified as significantly differently expressed genes. Exogenous ABA was found to enhance the transcription of genes involved in pigments metabolism, including carotenoids biosynthesis and chlorophyll degradation, whereas NDGA treatment inhibited these processes. The results also revealed the crucial role of ABA in flavonoids synthesis and regulation of antioxidant system. Intriguingly, we also found that an inhibition of endogenous ABA significantly enhanced the transcriptional abundance of genes involved in photosynthesis. Our results highlighted the significance of ABA in regulating tomato ripening, which provided insight into the regulatory mechanism of fruit maturation and senescence process.
Highlights
The plant hormone abscisic acid (ABA) has been considered to be mostly associated with regulation of non-climacteric fruit ripening in previous reports [1,2,3,4]
The expression level of genes encoding rate-limiting enzymes PSY, DXS and GGPS did not show any significant changes, indicating that the enhanced carotenoids in ABA deficient mutants was not due to the up-regulation of key genes expression [15]. Apart from these natural mutants, the RNAi-mediated suppression of key enzyme NCED lead to an obstruction for ABA biosynthesis, which could increase the carotenoids accumulation in the transgenic tomato [71]. The explanation for this phenotype could be that the reduced activity of NCED may cause the inhibition of carbon flux to ABA biosynthesis, so the ‘back-logged’ carbon transformed into upstream carotenoids production by up-regulation of PSY, PDS, GGPS and LCYB transcription in the RNAi lines [71]
Consistent with many previous researches, our result suggested that the high level of ABA could induce degreening process, possibly via enhancing expression of key enzymes involved in the chlorophyll degradation [86,87,88,89]
Summary
The plant hormone abscisic acid (ABA) has been considered to be mostly associated with regulation of non-climacteric fruit ripening in previous reports [1,2,3,4]. It has been confirmed that ABA is able to influence the ripening process of climacteric fruit, such as tomato, banana, peach, mango and melon [5,6,7,8,9]. Mounting evidences suggested that exogenous ABA could accelerate fruit maturation with promotion of many ripening-related biological events. Decreased fruit firmness was observed in ABA-treated mango fruit, which resulted from higher activities of enzymes involved in fruit softening [9]. Exogenous ABA was found to affect tomato fruit pigmentation with carotenoids accumulation.
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