## 3 Discussion
### Metabolome and Transcriptome Analysis of the Metabolite Biosynthesis Pathway  
The correlation between metabolites and genes was represented by a network diagram; a total of four metabolites were found to be positively correlated with related genes. These metabolites were mws4002, dopamine (alkaloids); mws2125, phosphoenolpyruvate (organic acids); pme0516, inositol (saccharides and alcohols); and mws0853, sinapyl alcohol (phenolic acid). It is well known that genes with different functions will form different metabolites and that different metabolites are related to genes with different functions. Four common KEGG pathways were found in this study. The polyphenol oxidase (PPO) genes (_LOC110105187_ and _LOC110105188_) and dopamine are co-enriched in the tyrosine metabolism (k00350) pathway, and both showed an upward trend. _PPO_ encodes polyphenol oxidase, which was also associated with catechol oxidase activity (GO:0004097), the pigment biosynthetic process (GO:0046148), the chloroplast thylakoid lumen (GO:0009543), and metal ion binding (GO:0046872). It catalyzes the oxidation of o-diphenyl and/or monophenols to form o-quinones while reducing oxygen to water, resulting in protein complexation and the formation of brown melanin pigments [47]. The acyl-coenzyme A oxidase 4 (ACX4) gene (_LOC110113353_) and phosphoenolpyruvate are co-enriched in the carbon metabolism (ko01200) pathway, and both showed a downward trend. _ACX4_ encodes acyl-coenzyme A oxidase 4, which was also associated with glyoxysome (GO:0009514), acyl-CoA dehydrogenase activity (GO:0003995), peroxisome (GO:0005777), flavin adenine dinucleotide binding (GO:0050660), embryo development ending in seed dormancy (GO:0009793), short-chain fatty acid metabolic processes (GO:0046459), and fatty acid \(\beta\)-oxidation (GO:0006635). The decreased _ACX4_ expression in several _Arabidopsis_ backgrounds showed a differential response, indicating that the _ACX4_ gene and/or protein have different functions in _Arabidopsis_ accessions [48]. The galactinol synthase (_GolS_) gene (_LOC110114431_) and inositol are co-enriched in the ABC transporters (ko02010) pathway, and both showed an upward trend. _GolS_ encodes galactinol synthase, which was also associated with the cytoplasm (GO:0005737), inositol 3-\(\alpha\)-galactosidaseity(GO:0047216), carbohydrate storage (GO:0052576), metal ion binding (GO:0046872), the galactose metabolic process (GO:0006012), the cellular response to cold (GO:0070417), and the raffinose family oligosaccharidesucharide biosynthetic process (GO:0010325). It catalyzes the critical step of raffinose family oligosaccharidesucharide biosynthesis and may play multiple roles in both the response to pathogens and assimilate loading [49]. The caffeoyl-CoAO-methyltransferase transferase (_CCoAOMT_) gene (_LOC110092466_) and sinapyl alcohol were co-enriched in the phenylpropanol biosynthesis (ko00940) pathway, and both showed a decreasing trend. _CCoAOMT_ encodes caffeoyl-CoA O-methyltransferasease, which was also associated with metal ion binding (GO:0046872) and O-methyltransferasease activity (GO:0008171). In addition, _CCoAOMT_ is an important gene that is involved in promoting the clearance of reactive oxygen species and lignin synthesis, thereby conferring drought stress tolerance in _Paeonia osti_[50]. These results indicate that the metabolism of tyrosine, carbon, and sinapyl alcohol in _D. nobile_ reduces to varying degrees. In addition, the ABC transporter pathway was increased to varying degrees in _D. nobile_. Therefore, it can be inferred that there are various regulatory mechanisms in organisms and that metabolites and genes have different regulatory patterns. Dendrobine is a sesquiterpenoid alkaloid with a typical picrooxane-type sesquiterpene skeleton structure [16]. The MVA pathway is involved in dendrobine biosynthesis. After MeJA treatment, dendrobine was significantly accumulated (7 d and 14 d).