Isolation and characterization of a heat-induced gene, hcit2, encoding a novel 16.5 kDa protein: expression coincides with heat-induced tolerance to chilling stress.

Heat treatment of tomato fruits induces tolerance to chilling injury. We have previously shown that specific heat-shock proteins (HSPs) are expressed in heated tomato fruits after cold storage. To search for heat-induced genes that are expressed at low temperatures, a cDNA library prepared from pre-heated chilled tomato fruits was differentially screened. A novel cDNA clone, hcit2, encoding a protein of ca. 16.5 kDa, was isolated. The predicted protein contains three putative trans-membrane hydrophobic sequences, suggesting that the protein is membrane-localized. The expression of hcit2 in fruits was induced by high temperature, but not by other stresses such as low temperature, drought or anaerobic conditions, and not during fruit ripening. A high level of hcit2 transcript was found in heated fruits after 2 weeks at 2 degrees C. High temperatures also induced hcit2 expression in tomato leaves, flowers and stems. The HCIT2 protein may be involved in the acquisition of tolerance to chilling injury.