Molecular cloning of a ripening-related expansin cDNA in peach: evidence for no relationship between expansin accumulation and change in fruit firmness during storage

A cDNA (PchExp 1) encoding a ripening-regulated expansin was isolated from ripe peach fruit. PchExp 1 encodes a predicted protein of 252 amino acids including the predicted signal sequence. The phylogenetic tree based on the deduced amino acid sequences indicated that PchExp 1 was most closely related to apricot PaExp2 and strawberry ripening-regulated FaExp2, and distantly to tomato ripening-regulated LeExp 1. The accumulation of PchExp 1 mRNA was fruit-specific and ripening-regulated. Furthermore, it was enhanced abundantly in 6 h by ethylene treatment. However, the patterns of PchExp 1 mRNA abundance in the ripe fruit of Akatsuki, which lost its firmness rapidly after harvest, and Yumyeong, which retained its firmness after harvest, were very similar during storage for eight days, irrespective of their different traits regarding changes in fruit firmness. The accumulation of protein recognized by the antibodies for LeExp 1 is also detected in the ripe fruit of Yumyeong. The present study suggests that PchExp 1 may play an important role in peach fruit ripening, but the accumulation of PchExp 1 may not regulate the changes in fruit firmness during storage of the peach.