Single and double mutations in tomato ripening transcription factors have distinct effects on fruit development and quality traits

The study of climacteric fruit ripening in tomato has been facilitated by the spontaneous ripening mutants Colorless non-ripening (Cnr), non-ripening (nor), and ripening inhibitor (rin). These mutants effect the genes encoding ripening transcription factors (TFs) SPL-CNR, NAC-NOR, and MADS-RIN causing pleiotropic defects to the ripening program. Here, we demonstrate that some ripening processes occur in the mutant fruit but at later stages of development compared to the wild type. The rin and nor mutant fruit exhibit similar quality traits to wildtype at later stages of ripening and senescence and delayed expression of ripening-associated genes. In addition, we propose that the Cnr mutant has a broader range of effects to fruit development than just fruit ripening. Cnr fruit show distinct differences from wild type in ripening phenotypic traits and gene expression profiles prior to the initiation of ripening. We provide new evidence that some mutants can produce more ethylene than basal levels and demonstrate ABA accumulation is also affected by the mutations. Studies have examined the relationship between the CNR, RIN, and NOR TFs based on protein-protein interactions and transcriptional regulation during fruit ripening. We describe the genetic interactions affecting specific fruit traits by using homozygous double mutants. Cnr predominantly influences the phenotype of the Cnr/nor and Cnr/rin double mutants but additional defects beyond either single mutation is evident in the transcriptome of the Cnr/nor double mutant. Our reevaluation of the Cnr, nor, and rin mutants provides new insights the utilization of the mutants in breeding and studying fruit development.