Fruits and vegetables undergo various regulatory mechanisms during growth, development, postharvest process and stress responses, all of which are crucial to their quality. An important mechanism involves the ubiquitin-proteasome system, in which E3 ubiquitin ligases play key roles by targeting specific proteins for modification and degradation, thereby facilitating various cellular functions. Multiple E3 ubiquitin ligases have been identified in fruit and vegetables, and research on these ligases is gradually increasing. However, a comprehensive understanding of E3 ligase regulation in a wide range of fruits and vegetables is lacking. This article introduces different types of E3 ubiquitin ligases and highlights their regulatory functions and mechanisms in the growth, development, and stress responses of fruit and vegetables in recent years, providing a theoretical basis for further exploration of their roles.

The alleviating effect and mechanism of cold shock pretreatment (-2 ℃ cold air for 3 h) on flesh browning in fresh-cut pitaya fruit was explored by evaluating its effect on the phenylpropanoid pathway and antioxidant system during storage. Results revealed that cold shock pretreatment efficiently inhibited the increase in electrical conductivity and malondialdehyde (MDA) content compared with the control. Cold shock pretreatment promoted the gene expression and activities of key enzymes (phenylalanine ammonia lyase, cinnamic acid 4-hydroxylase, and 4-coumarate-CoA ligase) related to phenylpropane biosynthesis, and improved the accumulation of total phenolics and flavonoids, as well as most individual phenolic compounds, which led to enhanced antioxidant capacity. The activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were increased by cold shock pretreatment. In addition, cold shock pretreatment accelerated the production of superoxide anion and H₂O₂ at the early stage of storage, but had no effect on their peaks and led to lower levels of superoxide anion and H₂O₂ afterwards, alleviating flesh browning in fresh-cut pitaya fruit. These results indicated that cold shock pretreatment can effectively alleviate wound-induced oxidative stress by modulating the phenylpropanoid pathway and reactive oxygen species (ROS) metabolism, thus inhibiting flesh browning in fresh-cut pitaya fruit.

Ethylene response factors 2 (ERF2) are essential for plant growth, fruit ripening, metabolism, and resistance to stress. In this study, the expression levels of the genes for MdERF2 implicated in the biosynthesis, composition and ultrastructure of fruit cuticular wax in apple (Malus domestica) were studied by the transfection of apple fruit and/or calli with MdERF2-overexpression (ERF2-OE) and MdERF2-interference (ERF2-AN) vectors. In addition, the direct target genes of MdERF2 related to wax biosynthesis were identified using electrophoretic mobility shift assays (EMSAs) and dual-luciferase reporter (DLR) assays. The findings indicated that the expression levels of four wax biosynthetic genes, long-chain acyl-CoA synthetase 2 (MdLACS2), eceriferum 1 (MdCER1), eceriferum 4 (MdCER4), and eceriferum 6 (MdCER6), were upregulated by ERF2-OE. In contrast, the expression levels of these genes were inhibited when MdERF2 was silenced. Furthermore, the overall structure and accumulation of fruit cuticular wax were influenced by the expression level of MdERF2. Treatment with ERF2-OE significantly increased the proportions of alkanes and ketones and reduced the proportions of fatty acids and esters. In addition, the EMSAs and DLR assays demonstrated that MdERF2 could bind directly to GCC-box elements in the promoters of MdLACS2, MdCER1, and MdCER6 to activate their transcription. These results confirmed that MdERF2 targets the up-regulation of expression of the MdLACS2, MdCER1, and MdCER6 genes, thereby altering the composition, content, and microstructure of apple epidermal wax.

To investigate the roles of Harvista (a sprayable 1-methylcyclopropene, 1-MCP, available component is 150 g·hm^-2) and Ethephon (1 mL·L^-1) applied at preharvest in apple (Malus domestica Borkh. 'Golden Delicious') fruit cuticular wax biosynthesis, the expression of genes related to fruit cuticular wax biosynthesis and ethylene biosynthesis and signaling, ethylene production rate, respiration rate, wax constituents and structure, and fruit quality were determined at harvest and during cold storage. The results showed that 1-MCP inhibited the expression levels of ethylene biosynthesis and signaling-related genes, decreased fruit ethylene production, and inhibited the expression of MdLACS1, MdCER6, MdCER4 and MdWSD1, which resulted in decreases in alcohols, acids, and esters content in fruit cuticular wax. 1-MCP also reduced fruit dropping rate from 17.17% to 12%; maintained fruit firmness, soluble solids, titratable acidity during cold storage; showed about as one fifth in the total length and one third in the widest width of wax crack as that in control at harvest. In contrast, Ethephon produced the opposite effects. In conclusion, 1-MCP inhibited fruit ethylene biosynthesis and signaling, and influenced fruit cuticular wax biosynthesis. Thus, the fruit cuticular wax constituents and structure was altered, and the fruit quality were maintained at harvest and during cold storage. The results provide a new technology for improving apple fruit harvest and postharvest quality by preharvest application of sprayable 1-MCP.