Developing pineapples with an extended shelf life through deletion of the abscisic-acid-responsive element in the enhancer sequence of the 1-aminocyclopropane-1-carboxylate synthase gene AcoACS1

Introduction: Pineapple fruits are frequently discarded because of softening. Non-climacteric fruit ripening is regulated by abscisic acid. Pineapple is a non-climacteric fruit. Ethylene participates in pineapple ripening. However, whether abscisic acid regulates pineapple ripening and the relationship between abscisic acid and ethylene in pineapple fruit have not been reported. Methods: Pineapple mutant lines were generated using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9). The ethylene content, abscisic acid content, respiration rate, fruit firmness, aroma profiles, and the activities of polygalacturonase, pectin methylesterase, β-galactosidase, xylanase, and cellulase in pineapple flesh were measured. Quantitative real-time reverse transcription polymerase chain reaction was performed to analyze the expression of the 1-aminocyclopropane-1-carboxylate synthase gene AcoACS1 across different pineapple lines. Results and discussion: Both abscisic acid and ethylene can induce pineapple ripening and softening. Ethylene content in pineapple fruits can be stimulated by abscisic acid. An abscisic-acid-responsive element in the enhancer sequence of the 1-aminocyclopropane-1-carboxylic acid synthase gene AcoACS1 was identified. After this element was knocked out, the expression of AcoACS1 was not induced by abscisic acid treatment, and the onset of pineapple softening was delayed. Aroma compound contents in the mutant fruit and Tainong 17 were similar. Abscisic acid induces pineapple ripening via the abscisic-acid-responsive element in AcoACS1. Pineapples with a long shelf-life can be generated through knocking out this element in AcoACS1.