Fruit Phenotype Analysis of SlSAHH2-CRISPR Tomato and Methylation Mechanism of SlSAHH2 Promoting Fruit Ripening

S-adenosyl-l-homocysteine hydrolase (SAHH EC 3.3.1.1) is a key enzyme that maintains methylation homeostasis. In this study, the knockout of SlSAHH2 delayed tomato fruit ripening. Compared with the wild type (WT), most ripening-related biochemical characteristics were significantly reduced in SlSAHH2-CRISPR fruits. Additionally, the expression of genes related to ethylene synthesis and ripening was generally down-regulated. In transcriptome data, a total of 3701 up-regulated and 3134 down-regulated differentially expressed genes (DEGs) were identified and analyzed. Bisulfite sequencing PCR (BSP) results showed that the methylation levels of the promoters of ethylene-related genes in SlSAHH2-OE fruits were higher. Furthermore, in the presence of a methylation inhibitor, the expression of E4, E8, ACO1, ACO3, and ACS2 was generally up- or down-regulated in SlSAHH2-OE or SlSAHH2-CRISPR fruits, respectively. In summary, it can be inferred that in the balance between methylation and ethylene synthesis, SlSAHH2 was more inclined to promote the latter process during tomato fruit ripening.