Two ω-3 FADs Are Associated with Peach Fruit Volatile Formation

Abstract

Aroma-related volatiles, together with sugars and acids, play an important role in determining fruit flavor quality. Characteristic volatiles of peach fruit are mainly derived from fatty acids such as linoleic acid (18:2) and linolenic acid (18:3). In the present study, six genes encoding fatty acid desaturases (FAD) were cloned, including two ω-6 FAD genes (PpFAD2, PpFAD6) and four ω-3 FAD genes (PpFAD3-1, PpFAD3-2, PpFAD7 and PpFAD8). Heterologous expression of peach FADs in tobacco plants showed that PpFAD3-1, and PpFAD3-2 significantly reduced contents of 18:2, and accumulated significant higher levels of 18:3. In the case of volatiles, transgenic plants produced lower concentrations of hexanal and higher levels of (E)-2-hexenal. Consequently, the ratio of the (E)-2-hexenal and hexanal was about 5- and 3-fold higher than that of wild type (WT) in PpFAD3-1 and PpFAD3-2 transformants, respectively. No significant changes in volatile profiles were observed in transgenic plants overexpressing the four other peach FAD genes. Real-time quantitative polymerase chain reaction (qPCR) analysis showed that ripe fruit had high PpFAD3-1 and low PpFAD3-2 transcript levels. In contrast, high PpFAD3-2 and low PpFAD3-1 transcript levels were observed in young fruit. These results indicate a temporal regulation of these two ω-3 FADs during development and ripening, influencing peach fruit volatile formation.

Fruit volatilome profiling through GC × GC-ToF-MS and gene expression analyses reveal differences amongst peach cultivars in their response to cold storage

“…In peach PpFAD1 is also linked to the biosynthesis of lactones 30 , 39 . Here, PpFAD1 was much more highly expressed than PpFAD4 irrespective of storage condition.…”

“…In tomato, altering fatty acid composition by overexpression of FAD genes both influenced CI tolerance and modified fruit volatiles 38 . The role of plant FADs associated with volatile formation has not been extensively studied although in peach, ppFAD1 seems to be involved in the production of a precursor of lactones/esters 39 .…”

E-Nose and GC-MS Reveal a Difference in the Volatile Profiles of White- and Red-Fleshed Peach Fruit

“…Patterns of volatile components were applied to distinguish the Calanda peach cultivar from others, in order to protect the Designation of Origin and associated economic implication [ 7 ]. Moreover, significant changes in volatile profiles were observed during peach fruit development [ 8 , 9 ], ripening [ 10 , 11 ], and postharvest storage [ 12 , 13 ]. Correlation analysis revealed a relationship between volatiles and quality traits of peach fruit during ripening [ 14 ].…”

Altered fatty acid composition of Nicotiana benthamiana and Nicotiana excelsior leaves under transient overexpression of the cyanobacterial desC gene

“…It is currently believed that lipids are synthesized via the prokaryotic and eukaryotic pathways in plastids and endoplasmic reticulum (ER), respectively. Most plant FA desaturases involved in the formation of unsaturated FAs are also located in these cell compartments (Los et al 2013, Wang et al 2016, Dar et al 2017. The eukaryotic and prokaryotic pathways interact with each other through a reversible exchange of FAs between the plastids and ER, in particular, in the case of sequential desaturation of FAs by desaturases.…”

“…The Δ9 acyl-[acyl-carrier-protein] desaturase (Δ9 desaturase) plays the key role in the formation of unsaturated FAs necessary for maintaining the optimal liquid-crystal structure of plant cell membranes because it forms the first double bond in the FA chain (López Alonso et al 2003). For example, Δ9 desaturase converts stearic acid (18:0) into oleic acid (18:1) by introducing a double bond between the ninth and tenth carbon atoms in the FA acyl chain (Troncoso-Ponce et al 2016), thereby providing the substrate for other desaturases sequentially forming the second (position Δ12), third (Δ15), and subsequent double bonds (Napier 2007, Los et al 2013, Wang et al 2016, Dar et al 2017. Thus, the desaturation of 18:0 to 18:1 catalyzed by Δ9 desaturase is one of the crucial stages controlling the content of unsaturated FAs in the cells.…”