Gene expression during tomato ripening

The changes in mRNA content that occur during tomato ripening have been studied by translation in vitro and cDNA cloning. A number of ripening-related cDNA clones have been characterized by hybrid-select translation, Northern blotting and sequencing. Some of these clones appear to be ripening-specific, based on the results of hybridization to mRNA from roots, leaves, and unripe and ripe fruit. DNA and protein sequencing have identified a full-length clone for polygalacturonase, an enzyme synthesized de novo during ripening that plays an important role in the softening process. mRNAs for polygalacturonase and some other unidentified proteins are absent or reduced in amount in the ripening inhibitor mutant of tomato. The accumulation of new mRNAs in normal fruit at the mature green stage is stimulated by ethylene. The regulation of gene expression during ripening and the mechanism of ethylene action are discussed.