A 13-lipoxygenase, TomloxC, is essential for synthesis of C5 flavour volatiles in tomato

Abstract

C5 volatile compounds, derived from fatty acids, are among the most important contributors to consumer liking of fresh tomatoes. Despite their important roles in flavour, the genes responsible for C5 volatile synthesis have yet to be identified. This work shows that their synthesis is catalysed in part by a 13-lipoxygenase (LOX), TomloxC, the same enzyme responsible for synthesis of C6 volatiles. C5 synthesis is independent of hydroperoxide lyase (HPL); moreover, HPL knockdown significantly increased C5 volatile synthesis. This LOX-dependent, HPL-independent pathway functions in both fruits and leaves. Synthesis of C5 volatiles increases in leaves following mechanical wounding but does not increase in response to infection with Xanthomonas campestris pv. vesicatoria. Large reductions in C5 and C6 volatiles in antisense TomloxC knockdown plants were observed but those reductions did not alter the development of disease symptoms, indicating that these volatiles do not have an important defensive function against this bacterial pathogen.

Chilling-induced tomato flavor loss is associated with altered volatile synthesis and transient changes in DNA methylation

“…3A). The C5 volatile 1-penten-3-ol is dependent upon LoxC action (10), whereas the C6 volatiles require sequential activity of LoxC and HPL (9). The final step in the pathway, conversion of aldehydes to alcohols, requires ADH2 activity (11).…”

Tomato fruit volatile profiles are highly dependent on sample processing and capturing methods

“…Octanal, nonanal, (E)-2-heptenal, 2-methylpropanal, 6-methyl-5-hepten-2-one, phenylacetaldehyde and 2-isobutylthiazole were detected in tomato paste A but not in paste B. This probably indicates that most volatiles detected in tomato samples are mainly produced when precursors and biosynthetic enzymes of those volatile compounds meet each other after tissue disruption, as it has been documented for several biosynthetic pathways, either by de novo biosynthesis (Chen et al 2004;Shen et al 2014) or by the release of volatile aglycones accumulated as conjugates (Tikunov et al 2013). After tissue disruption, volatile analysis protocols usually include some time of Table 1 Tomato fruit volatile profiles are highly dependent on sample processing and capturing… incubation so that detectable levels of the volatiles are produced.…”

“…In the homogenized samples, gene expression is not operational and the only mechanisms altering the volatile composition would be either chemical or enzymatic involving preformed molecules. In fact, it has been described that the homogenization of the fruit would facilitate the contact between enzymes and substrates otherwise localized in different cellular compartments in the living cells, and this would be responsible for the burst of many volatiles, including many fatty acid derivatives (the so-called green leaf volatiles) and several phenylpropanoids (Chen et al 2004;Granell and Rambla 2013;Shen et al 2014). The more complete the homogenization (in the paste much more than in the sliced fruit), the higher the production of these compounds.…”

Genes and Genomic Regions Related to the Production of Volatile Compounds in the Tomato Fruit

“…Sliced and whole fruit procedures have the disadvantage that the analysis requires to be performed on the fresh sample, and a complex set up is needed when parallel simultaneous acquisition of volatiles from a high number of samples is required, such as when profiling breeding collections which are highly dependent on harvest time . Nevertheless, sliced fruit samples produce a reasonably rich volatile profile, with particularly high levels of short branched-chain compounds, and therefore this sample processing method has been useful for a large number of studies (Tieman et al 2006a(Tieman et al , 2006b(Tieman et al , 2007Mathieu et al 2009;Vogel et al 2010;Goulet et al 2012;Mageroy et al 2012;Shen et al 2014). In fact, this sample processing technique is particularly useful when these volatiles are of particular interest, since it allows the detection of a higher number of such compounds.…”

“…Several genes have been characterized involved in the biosynthesis of fatty acid-derived volatiles (Matsui et al, 2000, Chen et al, 2004, Shen et al, 2014, Matsui et al, 2007, Speirs et al, 1998, apocarotenoids (Simkin et al, 2004), esters , Goulet et al, 2015, phenylpropanoids , other phenylalanine-derived volatile compounds (Tieman et al, 2006a, Tieman et al, 2007 and the role of conjugation in the accumulation and emission of volatiles (Louveau et al, 2011, Tikunov et al, 2013. Nevertheless, we have only achieved a partial knowledge of the metabolic pathways and the genes involved in volatile biosynthesis and regulation.…”