Yu Hou

Banana fruit is susceptible to chilling injury (CI) during low‐temperature storage, which results in economic loss. Ferulic acid (FA) is an endogenous phenolic chemical derived from phenylpropanoid pathway and involves in stress response. This study investigated the effect of FA on the cold resistance of banana fruit under 6°C storage for 7 days. Fruits were sampled at Days 0, 1, 3, 5, and 7. Indicators that associated with the occurrence and development of CI were detected. In comparison with control, 3 mM FA treatment significantly alleviated chilling symptoms and reduced CI index, malondialdehyde (MDA) content, and electrolyte leakage by 28.64%, 5.21%, and 9.12% averagely over storage. FA also inhibited the production of hydrogen peroxide (H₂O₂) and superoxide radical (O₂^−.), increased superoxide dismutase (SOD) and catalase (CAT) activities, as well as ascorbic acid (AsA), glutathione (GSH), total phenolic, and flavonoid contents. Phenylpropanoid metabolic pathway was also enhanced in FA‐treated fruit, as phenylalanine ammonia lyase (PAL) activity increased and expression levels of genes, including PAL, 4CL, C4H, and chalcone synthase (CHS), were upregulated. Additionally, FA treatment promoted energy supply by increasing contents of ATP and ADP, energy charge (EC), activities of Ca²⁺‐ATPase and H⁺‐ATPase, as well as expression levels of ATPase, H⁺‐ATPase, and Cyt b₆f. These findings suggested that FA might alleviate CI of banana fruit by regulating redox homeostasis, phenylpropanoid metabolism, and energy state.

Prenylation increases the structural diversity and biological activity of flavonoids. In this study, an aromatic prenyltransferase, FgPT1, was identified from Fusarium globosum. This enzyme was demonstrated to specifically catalyze the prenylation of flavanones, including naringenin, hesperitin, eriodictyol, liquiritigenin, rac-pinocembrin, and dihydrogenistein, and exhibited no activity toward other types of flavonoids, including chalcones, flavonols, isoflavonoids, and flavonols. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and nuclear magnetic resonance (NMR) analysis indicated that the majority of prenylated products were 6-C prenyl flavanones, with the exception of liquiritigenin, which was additionally transformed to 4′-O prenyl liquiritigenin. Enzyme kinetic analysis suggested that FgPT1 exhibited the highest catalytic efficiency towards naringenin, with a k_cat/K_M value determined as 61.92 s⁻¹ M⁻¹, and the lowest catalytic efficiency towards liquiritigenin, with a k_cat/K_M of 1.18 s⁻¹ M⁻¹. Biochemical characterization suggested that FgPT1 functioned as a metal-dependent enzyme with optimal activity in the presence of Ba²⁺ at pH 7.5 and 30 °C. Site-directed mutagenesis resulted in a series of mutants, including A325V with impaired prenylation activity and V116I, V181I, and V194I with enhanced activity. V194I displayed the highest enzymatic activity with a nine-fold increase compared to wild-type FgPT1.