Transcriptional Control of Tomato Fruit Ripening Is Mediated By Diverse Positive and Negative Regulators

Fruit are important sources of dietary nutrients, carbohydrates and fiber.  The process of fruit ripening coordinates numerous and often otherwise unrelated biochemical and physiological processes toward achieving optimal quality to make fruit tissues attractive and palatable to seed dispersing organisms.  Tomato is the primary model for fleshy fruit development and ripening in large part due to quantifiable physiological and metabolic phenotypes, tractable genetics, diverse germplasm stocks and the recent proliferation of genome resources.  Others and we have exploited these resources to identify necessary ripening transcription factors based on positional cloning of mutant loci and transcriptional profiling of fruit development, specific fruit tissues, and populations segregating for fruit phenotypes. The result has been a diverse set of transcription factors representing a range of gene families including MADS-box, NAC, AREBP, MYB, HBzip, homeodomain (HD), ERF, ARF, AUX/IAA and additional genes impacting fruit development and ripening.  Examples of both positive and inhibitory ripening effects have been documented for these genes.  Hierarchical relations among a number of these genes have been determined though the ripening regulatory circuitry is clearly complex and additionally influenced by developmentally regulated epigenome modifications that are in turn feed-back modulated by some of these transcription factors.  The current collection of functionally defined transcription factors is incomplete and additional candidates are emerging though QTL and transcriptome studies that will be highlighted.