Low expression of an endopolygalacturonase gene in apple fruit with long-term storage potential

Flesh softening during ripening differs greatly among apple cultivars. ‘Fuji’, the world's most popular cultivar, shows no detectable loss of firmness even in storage at room temperature for a month, whereas ‘Golden Delicious’ starts softening soon after harvest. To elucidate how softening patterns differ among cultivars, we analyzed four ripening-related genes (MdACS1, MdACO1, MdPG1 and MdExp3) in 14 cultivars, which display the firmness loss pattern of either ‘Fuji’ or ‘Golden Delicious’. All cultivars that remain firm revealed very weak or transient expression of MdPG1, irrespective of ethylene production rate and transcription levels of other genes. These results suggest that softening behavior during ripening may depend on the expression pattern of MdPG1.