## 1 Introduction  
Light is one of the most important regulators of plant growth and development. It also has a significant impact on the differential accumulation of isoprenoid-derived metabolites [1]. Although significant research has been carried out on light-controlled seedling morphogenesis, seed germination, shade-avoidance, and flower induction [2; 3; 4; 5], much less is known about how light regulates secondary metabolite biosynthesis, and about the regulatory mechanisms of monoterpenes biosynthesis. It has been reported that light intensity can alter terpenoid production via the activation of photosensitive enzymes involved in the methylerythntol phosphate (MEP) pathway [6]. Previous reports have shown that overexpressing Cryptochrome1 increased the amount of artemisinin in the medicinal plant _Artemisia amnu_ L. [7]. It has also been reported that the key transcription factor in the light signaling pathway, AaHY5, positively regulates the expression of genes involved in the artemisinin biosynthetic pathway [8].  
_Mentha_ L., belonging to the Labitatea family, is widely distributed and cultivated throughout the world. Because of their high economic value, _Mentha_ species have become one of the most important essential oil crops in the world [9]. In peppermint, the biosynthesis of monoterpenes though the MEP pathway in plastids involves several characterized enzymes, including geranyl diphosphate synthase large subunit (GPPS-I), geranyl diphosphate synthase small subunit (GPPS-s), limonene synthase (LS), (\(-\))-limonene-3-hydroxy (L3 OH), (\(-\))-trans-Isopiperitenol dehydrogenase (iPD), (\(-\))-isopiperitenone reductase (iPR), (\(+\))-cis-isopulegone isomerase (iPI), (\(+\))-pulegone reductase (PR), mentofuran synthase (MFS), and menthol dehydrogenase (MR). The relevant biosynthetic pathway is well understood, and all of the enzymes involved have been properly characterized [10]. Nevertheless, our understanding of the molecular mechanisms has revealed how the effects of the environment on monoterpenes biosynthesis are still unknown. Few transcription factors (TFs) have been reported to regulate monoterpenes biosynthesis. For instance, MsMYB negatively regulates monoterpenes production by binding to the _cis_-element of _MSGPPS_LSU_ and suppressing its expression [11]. The overexpression of _MsYABBY5_ was shown to lead to the increased production of terpen [12], but their mechanisms of signaling conduction, and the mechanism of the response of their signaling to environmental factors, were elusive.  
We investigated the effects of light on the densities of peltate glandular trichomes and on the chemical properties of the essential oil composition in mint leaves. High-throughput RNA-seq data were generated to screen expression profiles under the conditions of a 24 h darkness treatment and a recovery light period of 24 h. Differentially expressed genes (DEGs) of the light signal transduction pathway, as well as transcription factors and monoterpene biosynthetic genes, were identified, and their expression levels were compared. The results show that the expression of monoterpene biosynthesis genes is strongly downregulated by darkness, indicating their responsiveness to light. The results facilitate a further understanding of light signaling's functional regulation of monoterpenoids biosynthesis. A series of identified responsive transcription factors (TFs) could be used in metabolic engineering to effectively increase essential oil yields.