## 1 Introduction  
The genus _Mentha_ has important economic value for its abundance in essential oils that are widely used in the flavor, fragrance, and aromatherapy industries [1]. Monoterpenes are the major constituents of essential oils, which represent a large and diverse class of volatile C10 isoprenoids. The biosynthesis of monoterpenes originated in the upstream methylerythritol phosphate (MEP) pathway, then catalyzed by a series of enzymes. The catalytic mechanisms of monoterpene biosynthetic enzymes have been extensively studied in peppermint (_Mentha \(\times\) piperta_ L.) and spearmint (_Mentha spicata_ L.), two well-known _Mentha_ plants that have been employed as model systems for the study of monoterpene biosynthesis [2; 3; 4; 5; 6; 7]. In genus _Mentha_, a variety of monoterenes including (\(-\))-menthol, (\(+\))-neomethol, (\(+\))-isomenthol, (\(+\))-carvone, (\(+\))-menthofuran, and so on, are synthesized and stored in the peltate glandular trichomes on the aerial surfaces of the plant [8; 9]. The oil compositions vary in different _Mentha_ species and are regulated by transcriptional abundance, catalytic properties of enzyme catalysts, and cell type-specific epigenetic processes [9]. _Mentha canadensis_ L., as the largest cultivated aromatic plant in the world, is mainly cultivated in China. Not only in the aromatic industry, _M. canadensis_ is also widely used as a medicinal plant in traditional Chinese medicine [10]. The main component of _M. canadensis_ essential oils is menthol which accounts for more than 78% of the total essential oils' components [11]. Menthol is certainly the best-known monoterpene for its simple structure and wide applications. The earlier studies of _M. canadensis_ mainly focused on the identification of active compounds and activity assays [12; 13; 14]. Since the absence of sequence data, the molecular mechanism of menthol biosynthesis in _M. canadensis_ is still not clear. Only three menthol biosynthetic genes have been cloned in _M. canadensis_, including the Geranyl diphosphate synthase large subunit (GPPS-I), Geranyl diphosphate synthase small subunit (GPPS-s), and (\(-\))-Limonene synthase (LS) [15]. The phytohormone jasmonate (JA) is an important regulator in plant responses to biotic and abiotic stresses as well as other metabolic pathways by extensive reprogramming of gene expression [16; 17]. It is also an efficient elicitor of plant secondary metabolite production [18]. A lot of plant active ingredients including artemisinin, vinblastine, nicotine, taxol and ginseng may be transcriptional regulated by JA signal [19]. In _Artemisia annua_, high content of artemisinin could be produced in response to JA elicitor [20]. Some JA-responsive transcription factors (TFs) such as AaWRKY1, AaERF1, and AaERF2 could regulate the transcription of artemisinin biosynthetic genes and increase the accumulation of artemisinin [21; 22; 23]. So far, little is known about JA signal response and its effect on monoterpene biosynthesis in _M. canadensis_. The transcriptome sequencing technology is a useful method to carry out genome-wide gene discovery and expression profiling for its high-throughput and accuracy. It has been widely used to explore plants' physiological mechanism at the molecular level, such as model plants _Arabidopsis thaliana_[24] and _Oryza sativa_[25], as well as other non-model plants, such as _Brassica napus_[26], _A. annua_[27], and _Salvia miltiorrhizia_[28]. Using transcriptome sequencing, genome-wide changes in gene expression patterns under different treatment, such as hormone treatment, biotic and abiotic stress, could be easily accessed. For example, JA-mediated transcriptional reprogramming has been studied using RNA-seq in many plants, such as _A. annua_[27], _Taraxacum koksaghyz_[29], and _Gentiana macrophylla_[30]. In this study, high-throughput RNA-seq was applied to analyze the differential gene expression profiles of MeJ-treated _M. canadensis_ versus the control.