Pectate lyase gene expression and enzyme activity in ripening banana fruit

Two distinct cDNA clones showing sequence homology to higher-plant pectate lyase (Pel) genes were isolated from ripening banana fruits. The transcripts were detected only in fruit tissue and both were strongly ripening-related. Yeast transformation with the most highly expressed Pel clone produced a recombinant protein with pectate lyase activity, demonstrating that this sequence was likely to encode a pectate lyase protein in planta. An assay developed for measuring the action of the endogenous enzyme from banana pulp tissue revealed a significant increase in calcium-dependent pectate lyase activity during ripening. The enhanced levels of enzyme activity corresponded with an increase in soluble polyuronides from banana pulp.