# Plant Volatile Organic Compounds Evolution: Transcriptional Regulation, Epigenetics and Polylploidy
## 2 Biosynthesis and Epigenetic Regulation of VOCs
### Crosstalk between Fatty Acid Derivatives, Biosynthesis and Epigenetics  
Fatty acid derivatives such as (Z)-3-hexenol, 2-ketones and methyl jasmonate constitute the third major class of VOCs, which derive from C\({}_{18}\) unsaturated fatty acids, linoleic acids or linoleic acids. Biosynthesis of these compounds depends on the plasidic pool of acetyl-CoA generated from pyruvate (Pyr), the last product of glycolysis. The lipoxygenase (LOX) pathway leads to the formation of several VOC intermediates from two different branches. The allene oxide synthase (AOS) branch leads to the formation of jasmonic acid (JA), which is converted to methyl jasmonate by JA carboxyl methyl transferase [96]. In contrast to the AOS branch, the hydroperoxide lyase branch converts both 9- and 13-hydroperoxy intermediates into C\({}_{6}\) and C\({}_{9}\) aldehydes, which are often substrates for alcohol dehydrogenases, giving rise to volatile alcohols and their esters [97]. These saturated and unsaturated C\({}_{6}\)/C\({}_{9}\) aldehydes and alcohols, known as green leaf volatiles (GLVs), are usually synthesized in green plant organs of plants in response to wounding, and they also provide aroma to fruits and vegetables. However, these fatty acid derivatives are also important constituents of the floral volatile bouquet of several plant species (e.g., carnation, oil-secreting _Lysimachia_ and wild snapdragon) [98; 99; 100].  
The biosynthetic pathway of the volatiles derived from fatty acids is the least studied of all VOCs (Figure 1), but even less is known about its transcriptional regulation. Studies have usually focused on the defensive role of fatty acid derivatives and most of the information about their transcriptional regulation refers to jasmonate (JA) and its key role in the biosynthesis of other secondary metabolites [101; 102]. Many TFs, such as MYC (MYC2,3 and 4), MYB, EIN3, EIL, ERF, GAI, RGA and RGL1, may take part in the regulation of JA biosynthesis and coordination with other secondary metabolites [103]. For example, JA is part of the volatile sesquiterpene's regulatory transcriptional network and is controlled by ARF6 and ARF8 TFs [61].  
Recent studies have demonstrated a correlation between acetyl-CoA (a fatty acid volatile precursor), \(\beta\)-oxidation and the redox state of plant cells, which affect the global epigenetic pattern [104; 105]. Acetyl-CoA is produced by \(\beta\)-oxidation in plants and plays critical roles in development and secondary metabolite biosynthesis. Defects in the \(\beta\)-oxidation pathway may alter cells' redox state, affecting DNA methylation and histone acetylation in the nucleus [104; 106]. As biosynthesis of fatty acid derivative volatiles is affected by the redox state of cells (and vice versa) [107], it is conceivable that this represents an epigenetic component in its regulation. In this respect, other fatty acid derivatives not related to floral volatiles have been shown to be epigenetically controlled. In _Arabidopsis thaliana_ seeds, oil composition is altered by histone acetyltransferases which cause changes in the expression of genes from the fatty acid biosynthetic pathway [108]. Furthermore, in _Triticum aestivum_, TFs binding to the enoyl-CoA reductase gene promoter (a main component in wax biosynthesis) recruit histone acetyltransferases that alter their expression [109]. Although these biosynthetic pathways are not closely related to floral VOC biosynthesis, there may exist similar mechanisms regulating fatty acid derivatives, so further investigation is needed in this area.