Abstract: The postharvest economic quality of mature apple（Malus? × domestica Borkh.）is determined by the fruit shelf-life，which is associated with the fruit softening rate at room temperature. Ethylene is the factor that has been most studied in relation to the regulation of fruit softening. ACS（1-aminocyclopropane-1-carboxylate synthase）is one of the key enzymes in ethylene biosynthesis and pathway. Twenty ACS genes have been found by retrieving apple genome，two of which，MdACS1 and MdACS3，have been studied extensively due to their specific expression in fruit tissue. Recent characterization of these genes has provided insight into the molecular basis of ACS gene involvement in fruit ripening. This paper reviews the advances in our understanding of the role of ACS gene in apple fruit ripening and a model by which ACS regulating fruit ripening and ethylene production is proposed. In addition，we prospectively overview promising research avenues that could lead to further clarification of the regulatory events involved in ripening.

Key words: apple, fruit ripening, ethylene, shelf life, ACS