Biochemical and molecular regulation of tomato ripening and disease defense: A trade-off between quality and postharvest integrity.

Tomato (Solanum lycopersicum) fruit ripening is a complex, finely regulated developmental process that enhances sensory and nutritional quality but also compromises resistance to pathogens, especially necrotrophic fungi. This review synthesizes current insights into the hormonal, genetic, and epigenetic networks that coordinate tomato fruit ripening and immune responses. Ethylene acts as the central regulator of ripening, interacting with other hormones such as abscisic acid, brassinosteroids, auxin, jasmonic acid and salicylic acid to modulate both developmental and defense pathways. Key transcription factors, including MADS-RIN, NAC-NOR and SBP-CNR, orchestrate ripening while also influencing susceptibility. Epigenetic regulators including DNA and RNA methylation, histone modifications, and non-coding RNAs further integrate ripening and immunity. Ripening-induced changes, such as cell wall degradation, sugar accumulation, and decline in antimicrobial compounds, increase vulnerability to pathogens. However, elements of defense, including reactive oxygen species bursts, PR proteins, and hormone-mediated signaling, persist and can be enhanced. Understanding the ripening-immunity trade-off is vital for developing strategies to improve postharvest shelf life without compromising fruit quality. This review highlights the need for integrative approaches to manage postharvest tomato that aligns ripening dynamics with enhanced disease resistance.