Fruit aroma is an important organoleptic quality, which influences consumer preference and market competitiveness. Aroma compound synthesis pathways in plants have been widely identified, among the lipoxygenase pathway is crucial for fatty acid catabolism to form esters in apple. However, the regulatory mechanism of this pathway remains elusive. In this study, linear regression analysis and transgene verification revealed that the lipoxygenase MdLOX1a is involved in ester biosynthesis. Yeast one-hybrid library screening indicated that a protein, MdASG1 (ABIOTIC STRESS GENE 1), was a positive regulator of MdLOX1a and ester production based on yeast one-hybrid and dual-luciferase assays, as well as correlation analysis among eight different apple cultivars. Overexpression of MdASG1 in apple and tomato stimulated the lipoxygenase pathway and increased the fatty acid-derived volatile content, whereas the latter was decreased by MdASG1 silencing and CRISPR/Cas9 knockout. Furthermore, MdASG1 overexpression enhanced the salt-stress tolerance of tomato and apple ‘Orin’ calli accompanied by a higher content of fatty acid-derived volatiles compared to that of non-stressed transgenic tomato fruit, while MdASG1-Cas9 knockdown calli do not respond to salt stress and promote the biosynthesis of fatty acid-derived volatiles. Collectively, these findings indicate that MdASG1 activates MdLOX1a expression and participates in the lipoxygenase pathway, subsequently increasing the accumulation of aroma compounds, especially under moderate salt stress treatment. The results also provide insight into the theory for improving fruit aroma quality in adversity.

In this study, we analyzed the effects of treatments with titanium dioxide nanoparticles (NPs-TiO₂) and ethylene on anthocyanin biosynthesis and reactive oxygen species (ROS) metabolism during light exposure in ripe ‘red delicious’ apples. Both treatments led to improved anthocyanins biosynthesis in detached mature apples, while the NPs-TiO₂ had less impact on the fruit firmness, TSS, TA, and TSS/TA ratio. Furthermore, the effects of both treatments on the expression of anthocyanin-related enzymes and transcription factors in the apple peel were evaluated at the gene level. The differentially expressed genes induced by the two treatments were highly enriched in the photosynthesis and flavonoid biosynthesis pathways. The expression of structural genes involved in anthocyanin biosynthesis and ethylene biosynthesis was more significantly upregulated in the ethylene treatment group than in the NPs-TiO₂ treatment group, and the opposite pattern was observed for the expression of genes encoding transcription factors involved in plant photomorphogenesis pathways. In addition, the ROS levels and antioxidant capacity were higher and the membrane lipid peroxidation level was lower in fruit in the NPs-TiO₂ treatment group than in the ethylene treatment group. The results of this study reveal differences in the coloration mechanisms induced by NPs-TiO₂ and ethylene in apples, providing new insights into improving the color and quality of fruits.

Dwarfing rootstocks are widely used in apple production to control tree vigor and improve fruit quality. However, their adoption in ‘Fuji’ orchards remains limited by high production costs and unstable field performance. In this study, five rootstock materials, namely GM256, GM310, MD001, LiaoZhen 2, and Malus hupehensis Rehd (CK), were evaluated for their effects on cold tolerance, tree growth, and fruit quality in ‘Fuji’ apple. Cold tolerance was assessed using electrolyte leakage and related physiological indicators under low-temperature stress. MD001 and GM256 exhibited significantly stronger cold tolerance than the control, as indicated by lower LT₅₀ values and more favorable physiological responses (p < 0.05). Regarding tree growth, GM310 showed the weakest dwarfing effect, while LiaoZhen 2 had a relatively high proportion of long shoots, suggesting excessive vegetative growth. Meanwhile, GM256 produced the highest yield among all combinations. Principal component analysis of fruit-quality traits indicated that GM256 and GM310 performed better overall than the other combinations. In addition, GM256 produced significantly higher soluble solids, vitamin C content, and sugar–acid ratio than the control and most other rootstocks (p < 0.05). Overall, GM256 combined strong cold tolerance, a balanced shoot composition, moderate tree vigor, and high fruit quality, suggesting that it is a promising rootstock for ‘Fuji’ apple cultivation in Shandong Province.