Differential expression of genes and enzymes involved in cell wall degradation during ripening of strawberry cultivars

MARTINEZ GUSTAVO; ROSLI HERNAN; VILLARREAL NATALIA; BUSTAMANTE CLAUDIA; DOTTO MARCELA; CIVELLO PEDRO

Talca, Chile

Simposio; Post Harvest Fruit: the path to success; 2004

Strawberry is a non-climacteric fleshy fruit, which softens quickiy and has short post-harvest life. Cell wall disassembly contributes to fruit softening through the combined action of cell wall enzymes and proteins like polygalacturonases (PG), pectin methyl esterases (PME), endoglucanases (Egase), B-xylosidases (B-Xyl), B-galactosidases (B-Gal) and expansins (Exp), among others. We have compared the activity of these enzymes and the expression of polygalacturonase (spG), endoglucanase (FaCell) and expansin {FaExpl, FaExp2, FaExp5 and FaExpo) genes during ripening of two strawberry varieties with different fruit softening rates (Camarosa and Toyonaka, being the first one the firmest). PG activity was detected earlier, at White stage, in Toyonaka than in Camarosa, and the PG profile was different along ripening. PME increased during ripening until White stage and then remained constan!, without differences between varieties. Endoglucanase and B-Gal activities increased during ripening in both cultivars. Two B-Xyl activity peaks were found in Toyonaka along ripening, but oniy one in Camarosa. The activity of Egase, B-Gal and B-Xyl was higher in Toyonaka cultivar. Northern-blot analysis of spG, FaCell and FaXyll genes correlated with the corresponding enzyme activity data. In Toyonaka, spG and FaXyll expression was detected at high level from White stage to the end of ripening, while in Camarosa the expression of both genes began later. FaCell expression began in White stage and increased along ripening, and no difference between varieties was found. In the case of expansins, a clear correlation was found between the expression oí FaExpl, FaExp2 and FaExp5 genes and the difference in cultivar firmness, while no correlation in FaExp6 expression was evident. We conclude that the differences in firmness exhibited by these two strawberry cultivars correlate with a differential expression along ripening ofa set of genes and enzymes involved in cell wall disassembly, which includes at least three expansins, a polygalacturonase and a B-Xylosidase.