Molecular aspects of the strawberry fruit softening

Strawberry (Fragaria × ananassa Duch.) fruit softening during ripening is associated with the overlapping presence of two divergent endo-β-(1,4)-glucanases (EC 3.2.1.4; EGases), Cel1 and Cel2. Antisense down-regulation of both genes was performed to assess the precise role of these endo-β-(1,4)-glucanases on strawberry fruit softening. Constant down-regulation of cel1 expression throughout ripening was obtained, which was accompanied by reduced Cel1 protein accumulation. However, diminution of the Cel1 protein level together with a reduction of the total EGase activity to 40% of the control level did not affect fruit firmness, thus suggesting that Cel1 protein is not the major determinant of fruit softening during ripening. On the other hand, no significant reduction of Cel2 protein accumulation was found in any of the Cel2 transgenic or Cel1/Cel2 double-transgenic lines obtained. The difficulties encountered to yield a strawberry line with significant reduction of cel2 expression suggest that this gene might be playing a pivotal role on fruit development prior to ripening, thus accounting for the lack of Cel2 protein down-regulation observed.