The ability of plant hormones, mainly auxins and gibberellins, to induce fruit development in tomato is well known and has been used for some time and implies a role as signaling elements that mediate between the process of fertilization and subsequent fruit development.
To find out which genes are involved in tomato fruit set mediated by hormones, we performed comparative transcriptomic analysis of early development of both fertilized fruits and ovaries induced by hormone treatment to fruition. The analysis of the transcriptome results revealed that the greatest differences occur in the first days after induction, probably due to the higher speed of auxin to stimulate fruit set. Subsequently, the transcriptome of each treatment gradually come closer each other regardless of hormonal treatment or fertilization. The study revealed that there are elements that shape development programs in both a general component independently of the inducing agent, and a specific component of the hormone. Furthermore, in the specific case of gibberellins, the transcriptional study of SlDELLA gene silenced fruits, showed that this repressor controls at least a fraction of the transcriptional response to this hormone in the fruit. This response appears to include a series of defense mechanisms that are activated in the ovaries around anthesis. Moreover, transcriptomic and metabolomic study of the ripening pericarp of the fruit induced by hormone treatment, revealed that the effect of hormone treatment affects the expression of genes related to ethylene synthesis such as those that control the expression of ACC synthase and ACC oxidase, and results in fruit with significant alterations in the expression of genes involved in sugar metabolism such as sucrose synthase and those that encode several enzymes of glycolysis.
Besides, in order to extend the range of tools available for genetic engineering of fruit, a microarray analysis was carried out to identify specific gene expression in the ovary/fruit in order to clone fruit specific promoter sequences. Thus it was possible to build a collection of pENFRUIT Gateway vectors for a specifically-directed gene expression or silencing at different stages of tomato fruit development.
One of the isolated promoter sequences, PFF (3232 bp) showed a biphasic activity profile during fruit development: a peak of activity at the beginning of phase III and another at phase IV. The dotted spatial pattern in the late phase of activity, suggested the existence of a cell type (PPF (+)) or transcriptomic stage, associated with the fruit specific PFF promoter activity. Transcriptomic analysis of protoplasts PFF (+), revealed that this cell type or stage is defined by a gene expression program characterized by the increased expression of genes related to synthesis or management of sucrose, and decreased activity of protein synthesis and chromatin remodeling.