Ursolic acid (UA) inhibits browning of fresh-cut apple through MdMYB70 and MdbHLH62 mediated regulation of ascorbic acid (AsA) level

Enzymatic browning severely affects the quality of fresh-cut apple during processing and storage. Our previous study showed that exogenous UA effectively inhibits fresh-cut apple browning. However, the underlying molecular mechanisms remain unclear and we further observed that UA treatment significantly enhanced AsA accumulation. Here, we found that exogenous UA treatment facilitated endogenous UA biosynthesis. With the increase of UA, apple browning is alleviated. Transcriptome analysis revealed that MdGGP2 and MdAPX1, which were significantly affected by UA treatment, played important roles in regulating apple browning. Furthermore, gene correlation analysis and weighted gene co-expression network analysis (WGCNA) identified the transcription factors MdMYB70 and MdbHLH62 as important regulators responding to UA treatment. Functional assays demonstrated that MdMYB70 activated MdGGP2 expression to promote AsA biosynthesis, whereas MdbHLH62 repressed MdAPX1 expression to reduce oxidative consumption of AsA. Collectively, these results indicated that exogenous UA suppresses enzymatic browning in fresh-cut apple by coordinating MdMYB70/MdbHLH62 mediated AsA level. This study provides new insights into the molecular mechanisms underlying UA mediated regulation of enzymatic browning in fresh-cut apple.