The appearance of polygalacturonase mRNA in tomatoes: one of a series of changes in gene expression during development and ripening.

Tomato mRNA was extracted from individual fruits at different stages of development and ripening, translated in a rabbit reticulocyte lysate and the protein products analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The results indicate that there are at least two classes of mRNA under separate developmental control. One group of approximately six mRNAs is present during fruit growth and then declines at the mature-green stage. Another group of between four and eight mRNAs increases substantially in amount at the onset of ripening, after the start of enhanced ethylene synthesis by the fruit, and continues to accumulate as ripening progresses. Studies of protein synthesis in vivo show that several new proteins are synthesised by ripening fruits including the fruit-softening enzyme polygalacturonase. One of the ripening-related mRNAs is shown to code for polygalacturonase, by immunoprecipitation with serum from rabbits immunised against the purified tomato enzyme. Polygalacturonase mRNA is not detectable in green fruit but accumulates during ripening. It is proposed that the ripening-related mRNAs are the products of a group of genes that code for enzymes important in the ripening process.