The Fusion of MADS-Box Transcription Factors Has Transcriptional Activity and Modulates Expression of Many Ripening Genes.

Fruit development and ripening is regulated by genetic and environmental factors and is of critical importance for seed dispersal, reproduction, and fruit quality. Tomato () () mutant fruit have a classic ripening-inhibited phenotype, which is attributed to a genomic DNA deletion resulting in the fusion of two truncated transcription factors, and In wild-type fruit, RIN, a MADS-box transcription factor, is a key regulator of the ripening gene expression network, with hundreds of gene targets controlling changes in color, flavor, texture, and taste during tomato fruit ripening; , on the other hand, has low expression in fruit, and the potential functions of the fusion gene in ripening remain unclear. Here, overexpression of in transgenic wild-type cv Ailsa Craig tomato fruits impaired several ripening processes, and down-regulating expression in the mutant was found to stimulate the normal yellow mutant fruit to produce a weak red color, suggesting a distinct negative role for in tomato fruit ripening. By comparative transcriptome analysis of and :: RNA interference fruits, a total of 1,168 and 1,234 genes were identified as potential targets of RIN-MC activation and inhibition. Furthermore, the fusion gene was shown to be translated into a chimeric transcription factor that was localized to the nucleus and was capable of protein interactions with other MADS-box factors. These results indicated that tomato RIN-MC fusion plays a negative role in ripening and encodes a chimeric transcription factor that modulates the expression of many ripening genes, thereby contributing to the mutant phenotype.