Caffeic acid enhances storage ability of apple fruit by regulating fatty acid metabolism

"Qiujin" apple fruit was used as the materials to investigate the effects of exogenous caffeic acid on blue mold, quality parameters, and fatty acid metabolism. Results demonstrated that caffeic acid suppressed the lesion diameter of apple fruit inoculated with Penicillium expanusm, but did not significantly inhibit the colony diameter in vitro. Caffeic acid decreased malondialdehyde and citric acid contents, and inhibited the changes of color, but increased soluble solid, malic acid, and caffeic acid contents in apples. Caffeic acid also enhanced fatty acid synthase (FAS) and alcohol dehydmgenase (ADH) activities, whereas inhibited alcohol acyltransferase (AAT), hydmperoxide lyase (HPL), and lipoxygenase (LOX) activities in apples. Furthermore, caffeic acid increased MdACC, MdFAS, MdFabG, MdFabI, MdFabZ, MdMCAT, MdKASII, MdACP, and MdFAD expressions in fatty acid biosynthesis, and up-regulated MdKCS4, MdKCS6, MdKCS7, MdKCS10, MdACS4, MdACS8, MdCER10, and MdPAS2 expressions in fatty acid elongation, whereas down-regulated MdLOX, MdAAT, MdACD, MdECH2, and MdACOX3 expressions except MdADH expression in fatty acid degradation. Caffeic acid suppressed hexadecanoic acid and stearic acid contents, whereas promoted linolenic acid and linoleic acid contents in apples. These results suggest that exogenous caffeic acid could modulate fatty acid biosynthesis, elongation, and degradation to enhance disease tolerance and maintain the quality of apples.