Submitted to: Nature Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/14/2006
Publication Date: 9/4/2006
Citation: Manning, K., Tor, M., Poole, M., Hong, Y., Thompson, A., King, G., Giovannoni, J.J., Seymour, G. 2006. A naturally occurring epigenetic mutation in an sbp-box gene inhibits tomato fruit ripening. Nature Genetics. 38:948-952. Interpretive Summary: The Cnr mutation in tomato inhibits normal ripening and produces a severe phenotype, whereby fruit develop a colorless mealy pericarp. We interpret these results to mean that the gene at this locus could play a central role in the ripening process. This hypothesis is supported by observations on the biochemical and molecular events in Cnr fruits. Ripening-related carotenoid biosynthesis is absent in the mutant, with evidence for reduced ability to synthesize carotenoid precursors. The mealy texture of the fruit, with its greatly reduced cell-to-cell adhesion, reflects changes in the structure of Cnr cell walls and demonstrates an important role in texture manifestation. To place the Cnr gene product into a molecular framework that will help describe the ripening process it was necessary to clone the gene. Here we report on the cloning and characterization of the gene at the Cnr locus and show that it is a transcription factor or master regulator of the ripening process.
Technical Abstract: A major player in the regulatory network controlling fruit ripening is likely to be the gene at the tomato Colorless non-ripening (Cnr) locus 1,2. The Cnr mutation results in colorless fruits with a significant loss of cell to cell adhesion. The nature of the mutation and the identity of the Cnr gene are unknown. Here we demonstrate that an SBP-box (SQUAMOSA Promoter Binding Protein-like) gene resides at the Cnr locus by positional cloning and virus induced gene silencing (VIGS). Furthermore, the Cnr phenotype results from a spontaneous epigenetic change in the SBP-box promoter. The discovery that Cnr was an epimutation was unexpected as very few spontaneous epimutations have been described in plants 3,4. This study demonstrates that an SBP-box gene is critical for normal ripening and highlights the likely importance of epialleles in plant development and the generation of natural variation.