beta-xylosidase in strawberry fruit: Isolation of a full-length gene and analysis of its expression and enzymatic activity in cultivars with contrasting firmness

摘要

Strawberry is a non-climateric fleshy fruit, which softens quickly and has short post-harvest life. Ripening is associated with an increment of pectin solubility and a reduction of the content of hemicelluloses. In this work, we have cloned the full-length cDNA encoding a beta-xylosidase (FaXyl1) from Fragaria x ananassa and we have characterized its expression in two strawberry cultivars with contrasting fruit firmness. The analysis of the predicted protein showed that FaXyl1 is closely related to other beta-xylosidases from higher plants. The recombinant protein obtained by over-expressing FaXyl1 in Escherichia coli had beta-xylosidase activity against the artificial substrate p-nitrophenyl beta-D-xilopyranoside. Differently from other bifunctional xylosidases, no (X-L-arabinofuranosidase activity was detected in the recombinant enzyme. The expression of FaXyl1 gene was analyzed by northern-blot in Camarosa and Toyonaka strawberry cultivars, and compared with the corresponding protein data obtained by Westem-blot and with the beta-xylosidase activity during ripening. The softest cultivar (Toyonaka) showed an early accumulation of FaXyl1 transcript and a higher expression of the corresponding protein during ripening, which correlates with a higher P-xylosidase activity in all ripening stages analyzed. (c) 2006 Elsevier Ireland Ltd. All rights reserved.