Analyses of expression patterns of ethylene receptor genes in apple (Malus domestica Borkh.) fruits treated with or without 1-methylcyclopropene (1-MCP)

1-Methylcyclopropene (1-MCP) strongly inhibits ethylene-mediated ripening effects. Since 1-MCP binds irreversibly to ethylene receptors, and ethylene sensitivity is recovered through the appearance of new ethylene receptors, it is important to characterize ethylene receptor genes to understand 1-MCP efficacy. We isolated three putative ethylene receptor genes from apple fruit and examined Md-ETR1, Md-ERS1, and Md-ERS2 expression patterns in 1-MCP-treated and -untreated fruit of 'Orin' and 'Fuji'. In both cultivars, treatment with 1-MCP suppressed ethylene production and rapidly decreased expressions of Md-ERS1 and Md-ERS2, but Md-ETR1 mRNA was slightly reduced by the application of 1-MCP. One possible explanation for the high 1-MCP efficacy in apple fruits is that 1-MCP suppresses ethylene production and Md-ETR1 is expressed in 1-MCP-treated fruit. Md-ERS1 and Md-ERS2 mRNAs accumulated more abundantly in untreated 'Fuji', which has a long shelf life, than in 'Orin'. Since ethylene receptors negatively regulate ethylene signaling, differences in expression levels between the cultivars might be reflected in differences in ethylene sensitivity.