METHYLTRANSFERASE1 and Ripening Modulate Vivipary during Tomato Fruit Development.

Vivipary, wherein seeds germinate prior to dispersal while still associated with the maternal plant, is an adaptation to extreme environments. It is normally inhibited by the establishment of dormancy. The genetic framework of vivipary has been well studied; however, the role of epigenetics in vivipary remains unknown. Here, we report that silencing of METHYLTRANSFERASE1 (SlMET1) promoted precocious seed germination and seedling growth within the tomato (Solanum lycopersicum) epimutant Colorless non-ripening (Cnr) fruits. This was associated with decreases in abscisic acid concentration and levels of mRNA encoding 9-cis-epoxycarotenoid-dioxygenase (SlNCED), which is involved in abscisic acid biosynthesis. Differentially methylated regions were identified in promoters of differentially expressed genes, including SlNCED SlNCED knockdown also induced viviparous seedling growth in Cnr fruits. Strikingly, Cnr ripening reversion suppressed vivipary. Moreover, neither SlMET1/SlNCED-virus-induced gene silencing nor transgenic SlMET1-RNA interference produced vivipary in wild-type tomatoes; the latter affected leaf architecture, arrested flowering, and repressed seed development. Thus, a dual pathway in ripening and SlMET1-mediated epigenetics coordinates the blockage of seed vivipary.