Transcription factors (TFs) regulate gene expression through binding to cis-regulatory specific sequences in the promoters of their target genes. In contrast to the genetic code, the transcriptional regulatory code is far from being deciphered and is determined by sequence specificity of TFs, combinatorial cooperation between TFs and chromatin competence. In plants, organ development is a continuous process that expands beyond the embryonic phase and, as sessile organisms, plants have to face with a wide range of environmental stresses. Signaling cascades governing developmental and stress switches converge at the gene expression level. It is suggested that transcriptional regulation may play more important roles in plants than in animals, given the large number of TF-coding genes in plant genomes, ranging from 6% to 10%, depending on the database.

Fruit ripening is a developmental process evolved to foster animal-mediated seed dispersal, and considerable progress have been made through studies of tomato (Solanum lycopersicum), which is an important vegetable crop as well as the model plant for the Solanaceae family. The softening of fruits is an integral part of fruit ripening and is thought to be dependent to a large extent on cell wall metabolism. Many studies demonstrated association between changes in cell wall structure and cell wall hydrolases, including molecular studies performed to examine how manipulation of different cell wall hydrolase genes affect softening during ripening and postharvest storage. Most studies that examined the consequences of manipulating the cell wall metabolism were performed to examine the effect on texture or softening of fruit tissues. A recent study demonstrated that manipulation of cell wall hydrolases can be important to the postharvest qualities of leafy vegetables. Transgenic lettuce plants were generated in which the production of the cell-wall-modifying enzyme xyloglucan endotransglucosylase/ hydrolase (XTH) was downregulated. In transgenic plants the leaf area and fresh weight were decreased, whereas leaf strength was increased and membrane permeability was reduced toward the end of shelf life. Overall an extended shelf life of transgenic lines was observed relative to the non-transgenic control plants, which illustrated the potential for manipulation of cell-wall-related genes for improving postharvest quality of leafy crops.

A Photographs showing the progression of strawberry fruit development and ripening

Tomato fruit developmental stages

Pericarp color of litchi fruit