Isolation and characterization of the MiCel1 gene from mango:: ripening related expression and enhanced endoglucanase activity during softening

Fruit ripening is characterized by the progressive depolymerisation of cell wall polysaccharides of which the cellulose/hemicellulose network forms an important component. We have cloned an endo-beta-1,4-glucanase (EGase) homologue, MiCel1 from ripening mango (Mangifera indica var. Dashehari) that shows sequence similarity to higher plant EGase genes. The 2.3 kb cDNA of MiCel1 encodes a putative protein of 619 amino acids with a signal peptide that can direct it to cell walls. It also possesses a cellulose binding domain that is characteristic of microbial endoglucanases. Expression of MiCel1 is fruit specific and ripening related. There is a progressive increase in MiCel1 transcript accumulation during ripening that is correlated with increased EGase activity and associated with decrease in cellulose/hemicellulose content. In control (ethylene untreated) and 1-MCP treated fruit, ripening was delayed by around 3 days. This is associated with a delayed increase in MiCel1 expression and a delayed increase in EGase activity. It is proposed that expression of MiCel1 is closely associated with ripening and may play an important role in mango softening.