Determination of gene expression of some essential oil components and some genes responsible for the synthesis of these components in Mentha species harvested in different phenological periods

Peppermint (Mentha × piperita) is widely recognized as a significant medicinal plant worldwide. This study aimed to evaluate the gene expression levels of key genes involved in essential oil biosynthesis—limonene synthase (ls), limon-3-hydroxylase (l3oh), trans-isopiperitenol dehydrogenase (ipd), isopiperitenone reductase (ipr), menthol dehydrogenase (mdeh), and menthofuran synthase (mfs)—as well as the changes in various essential oil components across phenological stages in selected mint samples. The results revealed that the expression levels of genes associated with terpene biosynthesis varied among peppermint varieties. Additionally, seasonal variations were observed in the essential oil components of the studied varieties. While changes in the main chemical constituents were not always consistent with gene expression levels, some terpenes present in lower concentrations exhibited patterns that aligned with gene activity. Moreover, varieties displaying higher seasonal averages of gene expression levels were found to have higher overall essential oil content. This suggests that the genes studied play a broader role in the synthesis of terpene groups rather than being limited to the regulation of specific primary constituents. These findings provide important insights into the genetic and biochemical mechanisms regulating essential oil composition in mint. Such knowledge can contribute to the development of targeted breeding and cultivation strategies aimed at enhancing the medicinal and commercial value of peppermint.