## 1 Introduction  
As a part of the Lauraceae family, _Cinnamomum camphora_ (L.) [PERSON] is a deciduous tree with important economic value [1], and its economic value primarily depends on the quality and quantity of its essential oil. With the abilities of antibacterial and antifungal, the essential oil of _C. camphora_ has been wildly used in medicine and health [2, 3]. According to a previous study, _C. camphora_ essential oil can be extracted from the roots, stems, and leaves, and the extraction rate of essential oil from the leaves is the highest [1]. A previous study has verified that isoprenoids, also known as terpenoids, are the major components of _C. camphora_ essential oil [4]. Based on the different main components of the essential oil, _C. camphora_ can be divided into five chemotypes: isoborneol-type, camphor-type, cineole-type, borneol-type, and linalool-type [5]. As the main isoprenoid compound in linalool-type _C. camphora_, linalool is a kind of monoterene and is responsible for the characteristic flavor. At present, linalool has been commercially used in food, consumer products, insect repellents, and insecticides [6] for its anti-inflammatory [7], antimicrobial [8], and antioxidant properties [9]. To date, terpenoids are all derived from dimethylallyl diphosphate (DMAPP) and isopentenyl diphosphate (IPP). In plants, mevalonate (MVA) and methylerythnitol phos phate (MEP) are the two terpenoid precursor synthesis pathways [10]. The MEP pathway begins with the conversion of pyruvate and D-glyceraldehyde 3-phosphate (GAP) into 1-deoxy-D-xylulose 5-phosphate (DXP) which is catalyzed by DXP synthase (DXS). The DXP is converted to MEP by DXP reductoisomerase (DXR), which is subsequently reduced by 2-C-methyl-d-erythitol 4-phosphate cytidylyltransferase (MCT) to produce 4-(cytidine 5\({}^{\prime}\)-diphospho)-2-C-methyl-D-erythnitrol (CDP-ME). CDP-ME can be catalyzed to form 2-phospho-4-(cytidine 5\({}^{\prime}\)-diphospho)-2-C-methyl-D-erythnitrol (CDP-MEP) by 4-(cytidine 5\({}^{\prime}\)-diphospho)-2-C-methyl-D-erythnitrol kinase (CMK). 2-C-methyl-D-erythnitrol 2,4-cyclodiphosphate synthase (MDS) catalyzes the formation of 2-C-methyl-D-erythnitrol-2,4-cyclodiphosphate (MEcpp) directly from CDP-MEP. Under the catalysis of 4-hydroxy-3-methylbut-2-enyldiphosphate (HHBPP) synthase (HDS), MEcpp is converted to HMBPP, and then HMBPP can be catalyzed to produce both IPP and DMAPP by HMBPP reductase (HDR) [11]. The MVA pathway can produce IPP from acetyl-coenzyme A (CoA) via six consecutive steps catalyzed by acetyl-CoA C-acetyltransferase (AACT), 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase (HMGS), HMG-CoA reductase (HMGR), mevalonic acid kinase (MK), phosphomevalonate kinase (PMK), and mevalonate-5-diphosphate decarboxylase (MPDC). IPP isomerase (IPPI) catalyzes IPF to produce DMAPP [12]. IPP and DMAPP can produce various isoprenoid precursors catalyzed by short-chain preryltransferases: geranylfarnesyl diphosphate (GFPP), geranylgeranyl diphosphate (GGPP), farnesyl diphosphate (FPP), and geranyl diphosphate (GPP). Short-chain preryltransferases include GFP synthase (GFPPS), GGPP synthase (GGPPS), FPP synthase (FPPS), and GPP synthase (GPPS). GPP can further synthesize monoterpene, while GGPP can act as a precursor for the biosynthesis of carotenoids, tocopherols, phylloquinone, and diterpenes [10] (Supplement Figure S1). Recently, some studies provided insights into isoprenoid biosynthesis in _C. camphora_ based on sequencing technology. Eighty-three terpene synthase genes have been predicted and annotated in the chromosome-level genome sequence of _C. camphora_[13]. In addition to the investigation carried out on the genomic level, the analysis of genome-wide transcriptome also provides information about terpenoid biosynthesis in _C. camphora_[14]. Target identification analyses indicated that some microRNAs contributed to the regulation of terpenoid biosynthesis [15].