Gene Expression of Monoterpene Synthases Is Affected Rhythmically during the Day in Lavandula angustifolia Flowers

Lavender essential oil (EO) is widely used for medicinal purposes. The significant monoterpenes' abundance of linalool and linalool acetate accounts for more than 50% of lavender EO compounds. Monoterpenes synthesis differs throughout plant development as a result of the differential gene expression patterns in distinct cell types. Previously, we have reported that the chemical composition of Lavandula angustifolia cv. etherio EO was affected by diurnal harvest time. The aim of this was to evaluate if the gene expression of lavender monoterpenes synthases is altered during the day length and correlated with the accumulation of the major components of lavender EO. The relative expression of linalool synthase (LaLINS), limonene synthase (LaLIMS) and terpene synthase-like (LaTPS-l) was recorded in flowers at the 3rd to 5th stage every 3 h during two consecutive days using quantitative real-time PCR. The composition of the lavender EO was also monitored during the day length using GC-MS analysis. Our results indicate that the expression of genes involved in the synthesis of lavender EO, including linalool and limonene synthases, is accompanied by oscillations, picking at mid-day and leading to linalool acetate accumulation in the afternoon. In conclusion, the monoterpenes synthase expression in lavender flowers is rhythmically affected during the day, leading to a higher accumulation of EO compounds in the afternoon. These results will be helpful to monitor the biosynthesis of lavender EO to ensure a high-quality product. Furthermore, the outcome of this study will be useful for breeding programs in the lavender field to modulate the biosynthesis of linalool and linalool acetate during the flowering harvest period.