A CDNA CLONE HIGHLY EXPRESSED IN RIPE BANANA FRUIT SHOWS HOMOLOGY TO PECTATE LYASES

A cDNA clone (BanI7), encoding a protein homologous to pectate lyase, has been isolated from a cDNA library from climacteric banana fruit by means of differential screening. Northern analysis showed that BanI7 mRNA is first detected in early climacteric fruit, reaches a steady-st ate maximum at the climacteric peak, and declines thereafter in overri pe fruit. Accumulation of the BanI7 transcript can be induced in green banana fruit by exogenous application of ethylene. This demonstrates that expression of this gene is under hormonal control, its induction being regulated by the rapid increase in ethylene production at the on set of ripening. The deduced amino acid sequence derived from the BanI 7 cDNA shares significant identity with pectate lyases from pollen and plant pathogenic bacteria pi the genus Erwinia. Similarity to bacteri al pectate lyases that were proven to break down the pectic substances of the plant cell wall suggest that BanI7 might play a role in the lo ss of mesocarp firmness during fruit ripening.