Transcriptional regulation during tomato fruit development: Identification of novel genes involved in fruit ripening

A tomato (Solanum lycopersicum) cDNA microarray containing in excess of 1000 unique fruit-expressed cDNAs was developed and used to understand transcriptional circuitries during fruit development including ripening. We identified 364 unique differentially expressed sequence tags (ESTs) of which 117 were considered statistically significant at p ≤ 0.0000811 and the r247 were considered as interesting (p ≤ 0.05 but greater than 0.0000811). Forty-four percent of these encompass ESTs encoding unknown proteins or ESTs that show no match in the databases. Approximately 24% of the differentially expressed ESTs are involved in metabolism-and protein biosynthesis/degradation-related functions with more than 100 ESTs encoding genes involved in defense-, signaling-, transcription-, transport-, and cell structure-and cell wall-related functions. Expression profiling of these ESTs indicate that early fruit maturation and onset of ripening is perceived as a stress phenomenon since many defense-and stress-related genes are up-regulated at these stages. The mature green stage of the fruit appears to be a transcriptionally quiescent stage with a large number of differentially expressed ESTs showing more than a twofold decline in their transcript levels. A coordinated increase in expression profiles of many ESTs of unknown functions with those of documented functions in fruit development and ripening indicates a possible role for these ESTs in fruit development. Taken together, our results indicate that ripening is a transcriptionally active process with many stress-related genes being up-regulated during this stage of development.