Molecular Events Taking Place during Ripening of Fragaria chiloensis Fruit

The Chilean strawberry (Fragaria chiloensis) has emerged as a new berry for its exotic white-pink color and its outstanding aroma, however the fast softening limits its commercialization. The control of ripening in this non-climacteric fruit remains unclear, although auxins (Aux) and abscisic acid (ABA) may have a role on it. Aux levels decrease during ripening, albeit, ABA increases. Softening is related to cell wall disassembling and significant changes in the pectin and the hemicellulose fractions are observed during ripening of F. chiloensis fruit. In addition, several enzymes have been described to take part in its softening, including polygalacturonase (PG), xyloglucan endotransglycosylase/ hydrolase (XTH1) and expansin 2 (Exp2), among others. Transcripts level and enzyme activity for these genes increase during fruit softening. Also, the expression level of these genes varies significantly when fruits are treated with Aux or ABA. An activator effect of Aux on the expression of XTH1 and a repressive effect on PG were found. On the contrary, ABA induces the expression of both XTH1 and PG. To explain this regulatory mechanism, the promoter regions of these genes were obtained by Genome walker, and the in silico analysis reveals putative cis regulatory elements responding to hormones which could explain their differential responsiveness. These evidences provide useful information to understand the hormonal regulation during softening of F. chiloensis fruit.

Acknowledgments to Anillo ACT-1110 project.