Potential role of fatty acid desaturase 2 in regulating peach aroma formation

Fruit aroma is an important evaluation index for fruit quality. Linoleic acid is an essential precursor pool for the aroma compounds in peach (Prunus persica L.) and is catalyzed by fatty acid desaturase 2 (FAD2). In this study, PpFAD2–1 and PpFAD2–2 were isolated from ‘Jinxiuhuangtao’ peaches. Three typical conserved histidine motifs (HX3or4H, HX2or3HH, and HX2or3HH) were observed in the two PpFAD2 proteins, and 18 candidate amino acid residues potentially involved in fatty acid desaturation were identified in PpFAD2–1. Subcellular localization analysis indicated that PpFAD2s are localized in endoplasmic reticulum membrane. Notably, PpFAD2–1 expression was gradually increased during the fruit ripening stages, whereas PpFAD2–2 changed little. In vitro enzyme assay in both Escherichia coli and yeast revealed that PpFAD2s increased linoleic acid levels, with a larger increment of PpFAD2–1 than that of PpFAD2–2. Furthermore, in vivo enzyme activity assay revealed that levels of two unsaturated fatty acids (linoleic acid and linolenic acid) and peach aroma compounds (including hexyl acetate, γ-dodecalactone, γ-decalactone, γ-octalactone and γ-hexalactone) were increased in PpFAD2–1 transgenic fruit during postharvest storage, especially under recovery storage in room temperature after cold storage (4 ℃), whereas unchanged in PpFAD2–2 transgenic fruit. Favorably, this study provides new insights into the role of PpFAD2s in regulating peach aroma biosynthesis, which contributes to the sustainable fruit storage management and the molecular breading of new peach varieties with more favorable aromas.