Upregulation of two ripening-related genes from a non-climacteric plant (pepper) in a transgenic climacteric plant (tomato)

Activities of promoters from the capsanthin/capsorubin synthase and fibrillin genes, which are molecular markers for ripening in the non-climacteric pepper fruits, have been studied in transgenic tomato plants that produce fruits of the climacteric type (characterized by an increase in respiration and ethylene production). The promoters of both genes were strongly upregulated during tomato fruit ripening in a manner similar to the induction of these genes in pepper fruits. Induction occurred at the mature green stage preceding ripening (a stage when ethylene production and respiration are known to rise in tomato fruits). Ethylene positively influenced the expression of both genes in tomato. Other plant growth regulators, namely abscisic acid, auxin and polyamines, did not alter gene expression. In contrast, water loss strongly induced both promoters. This dehydration-mediated gene induction was inhibited by mitochondrial respiration inhibitors (mainly of the alternative oxidase). A slight positive effect with light, apparently not linked to normal photosynthesis but rather to photooxidative stress, was also observed. Taken together, the data indicate that activation of oxidase systems, leading to changes in the cellular redox balance, mediates the induction of both genes in tomato. Various cellular compartments are likely to be contributors to this process, which leads to the developmental regulation of nuclear genes encoding plastid-located proteins.