A cDNA clone (Banl7), 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 Banl7 mRNA is first detected in early climacteric fruit, reaches a steady-state maximum at the climacteric peak, and declines thereafter in overripe fruit. Accumulation of the Banl7 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 onset of ripening. The deduced amino acid sequence derived from the Banl7 cDNA shares significant identity with pectate lyases from pollen and plant pathogenic bacteria of the genus Erwinia. Similarity to bacterial pectate lyases that were proven to break down the pectic substances of the plant cell wall suggest that Banl7 might play a role in the loss of mesocarp firmness during fruit ripening.

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