β-xylosidase activity and expression of a β-xylosidase gene during strawberry fruit ripening

Abstract

Strawberry fruit shows a marked softening during ripening and the process is associated with an increment of pectin solubility and a reduction of the molecular mass of hemicelluloses. In this work, we report the activity of β-xylosidase and the expression of a β-xylosidase gene in strawberry fruit. We have cloned a cDNA fragment encoding a putative β-xylosidase (FaXyl1) from a cDNA library obtained from ripe strawberry fruit. The analysis of the deduced amino acid sequence revealed that FaXyl1 is closely related to other β-xylosidases from higher plants. The expression of FaXyl1 was strongly associated to the receptacle tissue although a low expression level was detected in achenes and ovaries. The accumulation of FaXyl1 mRNA is ripening-related, starting in white fruit, reaching the maximum at 25–50% red fruit and decreasing thereafter. The total β-xylosidase enzyme activity was detected in all ripening stages with the maximum in 25–50% red fruit. The low activity level detected in immature stages, where no expression of FaXyl1 was found, suggests the presence of other β-xylosidases-like genes. Both the expression of FaXyl1 and the total β-xylosidase activity were down regulated by auxins, as occurs for most of the ripening-related processes in strawberry fruit. A putative role of FaXyl1 and β-xylosidase is discussed.