The plant hormone abscisic acid (ABA) has been suggested to play a role in fruit development, but supporting genetic evidence has been lacking. Here, we report that ABA promotes strawberry (Fragaria ananassa) fruit ripening. Using a newly established Tobacco rattle virus-induced gene silencing technique in strawberry fruit, the expression of a 9-cis-epoxycarotenoid dioxygenase gene (FaNCED1), which is key to ABA biosynthesis, was down-regulated, resulting in a significant decrease in ABA levels and uncolored fruits. Interestingly, a similar uncolored phenotype was observed in the transgenic RNA interference (RNAi) fruits, in which the expression of a putative ABA receptor gene encoding the magnesium chelatase H subunit (FaCHLH/ABAR) was down-regulated by virus-induced gene silencing. More importantly, the uncolored phenotype of the FaNCED1-downregulated RNAi fruits could be rescued by exogenous ABA, but the ABA treatment could not reverse the uncolored phenotype of the FaCHLH/ABAR-down-regulated RNAi fruits. We observed that down-regulation of the FaCHLH/ABAR gene in the RNAi fruit altered both ABA levels and sugar content as well as a set of ABA-and/or sugar-responsive genes. Additionally, we showed that exogenous sugars, particularly sucrose, can significantly promote ripening while stimulating ABA accumulation. These data provide evidence that ABA is a signal molecule that promotes strawberry ripening and that the putative ABA receptor, FaCHLH/ABAR, is a positive regulator of ripening in response to ABA.

Although a great deal of progress has been made toward understanding the role of abscisic acid (ABA) in fruit ripening, many components in the ABA signalling pathway remain to be elucidated. Here, a strawberry gene homologous to the Arabidopsis gene ABI1, named FaABI1, was isolated and characterized. The 1641bp cDNA includes an intact open reading frame that encodes a deduced protein of 546 amino acids, in which putative conserved domains were determined by homology analysis. Transcriptional analysis showed that the levels of FaABI1 mRNA expression declined rapidly during strawberry fruit development as evidenced by real-time PCR, semi-quantitative reverse transcription–PCR, and northern blotting analyses, suggesting that the Ser/Thr protein phosphatase PP2C1 encoded by FaABI1 may be involved in fruit ripening as a negative regulator. The results of Tobacco rattle virus-induced gene silencing and PBI121 vector-mediated overexpression suggested that the down- and up-regulation of FaABI1 mRNA expression levels in degreening strawberry fruit could promote and inhibit ripening, respectively. Furthermore, alteration of FaABI1 expression could differentially regulate the transcripts of a set of both ABA-responsive and ripening-related genes, including ABI3, ABI4, ABI5, SnRK2, ABRE1, CHS, PG1, PL, CHI, F3H, DFR, ANS, and UFGT. Taken together, the data provide new evidence for an important role for ABA in regulating strawberry fruit ripening in the processes of which the type 2C protein phosphatase ABI1 serves as a negative regulator. Finally, a possible core mechanism underlying ABA perception and signalling transduction in strawberry fruit ripening is discussed.