Transcriptomic and Epigenetic Signatures of Tomato Fruit After Postharvest UV-C Irradiation Are Associated with the Maintenance of Fruit Quality

Exposure to UV-C irradiance effectively maintains fruit quality, however the mechanisms by which it ensures tomato postharvest quality remain unclear. We conducted a comprehensive analysis of the transcriptome, volatilome, DNA methylome, and RNA methylome of tomato fruit in order to construct a UV-C regulatory network. UV-C was found to induce the expression of hormones-related, flavonoid, and resistance genes, to delay senescence, and to promote the expression of sugar and acid metabolism genes, leading to the synthesis of soluble sugars and degradation of citric acid in a manner that maintains fruit taste characteristics. Volatilome results demonstrated that UV-C enhanced the accumulation of 3-methyl-2-butenal, ß-damascenone, and 6-methyl-5-heptene-2-one by regulating genes associated with the metabolism of these volatile organic compounds. Additionally, UV-C contributed to the retention of accessible chromatin regions (ACRs), with genes associated with plant hormones showing variation in expression corresponding to chromatin accessibility. UV-C also inhibited the decrease in DNA methylation during ripening, with dynamic changes in DNA methylation and RNA methylation of genes related to hormones, flavonoids, texture, and resistance, ultimately delaying fruit senescence. This study is the first to comprehensively elucidate the regulatory role of UV-C on tomato postharvest ripening and as such provides valuable insights into epigenetic modifications which could represent important tools for future quality-based breeding programs. Overall design: 'Original No. 1' fresh tomatoes at the firm red ripe maturity stage were harvested at the “Hehe Yuan” farm (Miyun District, Beijing, China) and transported to the laboratory within 1 h, and intact fruit were randomly divided into two groups of 200. Tomatoes were put into polyethylene boxes (crisper). One group was treated with UV-C light (TUV 30 W, Philips, Netherlands) at a dose of 4 kJ/m2, and the irradiation dose was measured by ultraviolet irradiation meter (LS125, Linshang, Shenzhen), while the other group was not treated in order to serve as a control. After irradiation, it is sealed with plastic wrap and stored at 20 ? in darkness. On day 8, the control group fruit had lost commercial value, so the fruit of 0 d (CK-0d) and 8 d (CK-8d and UV-C-8d) were selected for omics analysis (Transcriptome, volatile metabolome, DNA methylation, and RNA methylation). Each group randomly selected 10-12 fruit. The middle pericarp tissue tomatoes (containing epicarps, without seeds) were cut into pieces and mixed well, then immediately frozen with liquid nitrogen and stored in a refrigerator at -80°C. All experiments were parallel three times.