LAUSR

BACKGROUND Fruit softening is a major determinant of commercial value and shelf life. A transcriptomic analysis of 'Golden Delicious' and 'Golden Del. Reinders' (a bud mutation of 'Golden Delicious' that readily softens) apple fruit was conducted during storage. RESULTS A comparative analysis of the obtained expression profiles of fruit between two cultivars identified 1345 up-regulated and 3475 down-regulated differentially expressed genes (DEGs). The identified DEGs were associated with cellular processes and carbohydrate metabolism, and were especially enriched in cell-wall-related genes. Among the cell-wall-related genes, xyloglucan endotransglucosylase/hydrolases (XTH) gene, MdXTHB, was significantly up-regulated and exhibited high expression levels in 'Golden Del. Reinders' fruit, which had a lower level of firmness relative to 'Golden Delicious'. Overexpression of MdXTHB in both 'Golden Delicious' and 'Fuji', which typically maintain high levels of firmness in storage, exhibited faster rates of softening and an earlier peak of ethylene production compared to empty vector infiltrated fruit. CONCLUSION The results of the present study indicate that MdXTHB potentially promotes apple fruit softening by degrading the fruit cell wall. This result is also useful to designing further experiments on the molecular regulation of fruit softening in apple. This article is protected by copyright. All rights reserved.