## 3 Discussion  
The remarkable health and disease alleviation activities of the scared lotus are associated with the high content of bioactive compounds, including polyphenols, flavonoids, phenolic acids, alkaloids, terpenoids, steroids, fatty acids, and glycosides [23]. However,  
Figure 8: qRT-PCR and RNA-Seq analysis of 12 terpenoid-pathway-related candidate unigenes in sacred lotus. FPKM terms of various plants parts were determined by RNA-seq. Relative expression of genes was calculated using young leaves as control. Standard error of the mean for three biological replicates is represented by the error bars. _AACT_, Acetyl-CoA C-acetyltransferase; _HMGS_, _hydroxymethylglutaryl-CoA synthase_; _HMGR_, _hydroxymethylglutaryl-CoA reductase (NADPH)_; _FPPS_, _farnesyl diphosphate synthase_; _MVK_, _nevalonate kinase_; _MDS_, _2-C-methyl-D- erythroid_ _2,4-cycldiphosphate synthase_; _PMK_, _phosphomevalonate kinase_; _DXR_, _1-deoxy-D-xylulose-5-phosphate reductioisomerase_; _IDI_, _isopentenyl-diphosphate Delta-isomerase_; _DXS_, _1-deoxy-D-xylulose-5-phosphate synthase_. most studies focus on flavonoids, alkaloids, and phenolic acids, while few have been conducted on terpenoids [24; 25; 26]. In this study, in total, 21 terpenids were detected (Table 1). Although the genes involved in terpenoid biosynthesis are widely studied in different plants [20; 27; 28; 29; 30; 31; 32; 33], genes related to the synthesis of terpenoids in sacred lotus have not been studied so far. The precursors of monoterpenes and diterpenes come from the MEP pathway in plastids, while the precursors of sesquiterpenes and triterpenes come from the MVA pathway in the cytoplasm [34]. Considering the two rate-limiting enzymes, HMGR and DXS played important roles in the overall regulation of the MVA and MEP pathways, respectively [35; 36; 37]. Among five genes encoding HMGR identified in this study, _HMGR1_, _HMGR2_, and _HMGR4_ exhibited the highest expression in YL, with the lowest expression in ML (Figure 5). In total, three genes encoding DXS were detected; _DXS2_ and _DXS3_ had the same expression pattern, with higher expression in leaves than in seeds, and there was no significant difference in expression in the three colors of flowers, which corresponded to the metabolic content results. This result indicated that the distribution of terpenoids in different plant parts was closely related to the expression pattern of genes involved in the MVA and MEP pathways. However, the relative contribution of each pathway to the biosynthesis of various terpenoids was still uncertain. IPTS are the key enzymes that connect the upstream MVA and MEP pathways with downstream isoprenoid biosynthesis branch points of different structures. In recent years, GPPS, GGPPS, FPPS, and CPPS, as the key enzymes in the biosynthesis of isoprenoid compounds, were identified in higher plants. In addition, most studies showed that the transcription levels of these genes were closely related to the content of corresponding terpenoids [38; 39; 40; 41]. For example, FPPS overexpression increased the production of ganoderic acid [42]. A high number of monoterpenes was produced by overexpression of peppermint (_Menthu_\(\times\)_piperita_) _GPPS.SSU_ in transgenic tobacco plants [43] and the content of abietane diterpenes in _Salvia sclare_ L. hairy roots was increased by engineering the _GGPPS_ and _CPPS_[44]. In this research, six DEGs encoding IPTS were identified, including one _GPPS_, two _FPPS_, and three _GGPPS_. We found that the expression of _FPPS_ was higher in young leaves than in seeds and mature leaves, which is consistent with the results detected for the metabolic content of triterpenoids. It has been shown that the _GGPPS_ transcript was mainly concentrated in the above-ground parts, such as leaves, flowers, or fruits, and the expression patterns of different _GGPPS_ homologous genes in the same plant were various [45; 46; 47; 48; 49; 50; 51]; the expression patterns of _GGPPS2_ and _GGPPS3_ identified in this study are consistent with this conclusion.