Exploring the apple genome reveals six ACC synthase genes expressed during fruit ripening

Fruit ripening of apple is regulated by a plant hormone ethylene. Ethylene signaling is based on its biosynthesis in which ACC synthase (ACS) is the rate-limited enzyme and plays the most important role. By exploring the apple whole genome, we identified 19 ACS genes, and their expressions in fruit were investigated. Six ACS genes were expressed in fruit, including four new sequences. Out of these six genes, three were totally inhibited by 1-MCP (1-methylcyclopropene, an ethylene inhibitor), which were considered to work in System 2 ethylene; the others did not respond to 1-MCP, being considered to work in System 1 ethylene biosynthesis. This study showed that the whole genome can be used as a potential resource to identify new members of a multi-gene family important for a specific trait in apple.