SynopsisRipening of tomato and other fruits involves changes in quality attributes that make them attractive to consumers. These alterations are brought about by the coordinated expression of specific genes. Ethylene, synthesised by cells of climacteric fruit at the onset of ripening, stimulates the expression of genes required for ripening to occur. Experiments with transgenic plants have shown that a 5′ flanking region from the fruit polygalacturonase (PG) gene directs the ripening-specific expression of foreign genes in tomato. Antisense genes have also been used to down-regulate expression of the PG gene, causing a reduction in pectin degradation during ripening. This reduction in PG has beneficial effects on fruit storage life and processing characteristics. Antisense technology has also been used to assign functions to previously unknown genes. This has led to the identification of the gene for ethylene forming enzyme (EFE) which catalyses the terminal step in ethylene synthesis. Detached fruit from tomato plants in which EFE is inhibited by antisense genes produce much less ethylene and ripening is greatly slowed. The rate of ripening can be restored by adding ethylene externally. These results raise the possibility of manipulating ripening of many fruits and also of controlling processes such as abscission and senescence of leaves and flowers.
The Small Introns of Antisense Genes Are Better Explained by Selection for Rapid Transcription Than by “Genomic Design”
