Fig. 1

Hormone, transcription and epigenome changes regulating softening in tomato. Tomato fruit softening is directly or indirectly regulated by a range of transcription factors (TFs). These include RIN-MADS, SPL-CNR and TFs from the NAC-box family such as NOR-Like1 along with SlLOB1, SlFSR and SlHY5. Ripening-associated softening processes are initiated and modulated by complicated network of feedback and crosstalk among different phytohormones including ethylene (ETH), abscisic acid (ABA), auxin and gibberellic acid (GA). Direct links between hormones and fruit texture regulation have been observed during tomato fruit ripening. Modifications to the epigenome especially DNA methylation and histones and RNA methylation are associated with ripening-related softening. SlDML2 is a key player regulating demethylation during tomato ripening. SlALKBH2, active m6A RNA demethylase, is necessary for normal tomato fruit ripening by direct targeting and stabilising transcript of SlDML2. Histone deacetylases SlHDA3 and SlHDA1, polycomb-group proteins SlMSI1 and SlLHP1b along with epigenetic mark H3K27me3 function as negative regulators of fruit softening, while histone deacetylases SlHDT3 plays a positive role in tomato fruit softening