Expression of a water stress-induced polygalacturonase gene in harvested cucumber fruit

We investigated the molecular response of harvested cucumber (Cucumis sativus L.) fruit to postharvest water stress. Using RT-PCR, we isolated CUPG1 cDNA, a cDNA clone encoding polygalacturonase (PG) that is inducible by water stress in cucumber fruit and characterized the expression of the gene with respect to hormonal control. The full length sequence determined by RACE-PCR, encoded a deduced protein of 435 amino acids that contained several common conserved domains as reported for PGs. The CUPG1 gene expression was also induced by exogenous ethylene but not by the application of abscisic acid (ABA). The level of CUPG1 mRNA induced by water stress, was reduced by 50% in fruits pre-treated with 1-methylcyclopropene (MCP), a strong inhibitor of ethylene action, which suggests that the expression of CUPG1 gene could be induced by a direct mechanism through water stress and an indirect mechanism mediated through ethylene produced in response to water stress. We conclude that water loss in harvested cucumber fruit results not only in physical changes but also leads to molecular responses, including PG gene expression.