## 3 Discussion
### Transcriptome Analysis of D. noble  
The object of transcriptomics is usually the sum of all the RNA that can be transcribed by a cell in a given state and includes messenger RNA (mRNA) and non-coding RNA. This is a common experimental method for discovering new genes, quantifying gene expression, and identifying transcripts [42]. For example, many genes associated with alkaloids and terpenoids have been analyzed and identified by transcriptome sequencing in _Erythrina velutina_ [PERSON] [43] and _Panax ginseng_[44]. Although some genes (sesquietrepene synthases and post-modification enzymes) related to terpenoid biosynthesis have been identified in _D. noble_ infected with the mycorrhizal fungus MF23 (_Mycena_ sp.) [17], the genes related to alkaloid and terpenoid biosynthesis induced by MeJA have not been elucidated. In this study, on the basis of mycorrhizal fungus MF23 induction, _D. noble_ was treated with MeJA to screen genes related to the dendrohine biosynthetic pathway. A terpene synthase gene (Loc110109817) was obtained via qRT-PCR. The gene was highly expressed after MeJA treatment and reached its peak at 16 h. A sequence alignment analysis indicated that the gene was probably (\(\pm\))-germacrene D synthase, \(\alpha\)-humulene synthase, or \(\beta\)-patchoulene synthase, and the enzyme was identified as sesquiterpene synthase [31]. FPP was catalyzed by sesquiterpene synthetase to form a sesquiterpene skeleton, e.g., (\(\pm\))-germacrene D, \(\alpha\)-humulene, and \(\beta\)-patchoulene. In this study, it was found that the expression level of the gene Loc110109817 (SQS2) was positively correlated with the biosynthesis of dendrohine. Therefore, we speculate that SQS2 may be a sesquiterpene synthase that is involved in the biosynthesis of dendrohine. After MeJA induces gene changes in _D. noble_ plants, SQS2 might directly or indirectly affect the biosynthesis of dendrohine. In another study, the _DnSQS-2_ gene was introduced into and overexpressed in _Saccharomyces cerevisiae_ and the fermentation products were analyzed. It was found that DnSQS-2 was a multifunctional synthase that can catalyze the formation of monoterpenes, sesquiterpenes, diterpenes, triterpenes, triterpenes, and tetriterpenes. Of these, the sesquiterpene compound farnesol may be an intermediate compound in the synthesis pathway of dendrohine. TFs usually regulate the progression of genes, thereby controlling a variety of cellular processes and cellular states [45]. It is well known that TFs usually need to cooperate with RNA polymerase II to form a transcription initiation complex and then participate in the process of transcription initiation. Co-expression analysis indicated that 238 and 313 TFs may participate in the regulation of terpenoid and polysaccharide biosynthesis, respectively. Of these, ZAT11, NAC, MYB, ZIM, HD-ZIP, and bHLH are positively correlated with SQS2 levels, whereas B3, WRKY, CCCH, EREBP-1, BEL1, GRF6, and BTB/POZ are negatively correlated with SQS2 levels (Supplementary Table S2). In addition, various reports have demonstrated that there may be many types of sesquiterpene synthases in the same plant species and that these enzymes compete with each other for the common precursor (FPP) to synthesize various types of sesquiterpenes when consumed [17]. In this study, we screened a sesquiterpene synthase (_TPS21_) from the transcriptome of _D. noble_ infected with the mycorrhizal fungus MF23 and found that this enzyme was negatively correlated with the biosynthesis of dendrohine. Therefore, inhibiting or reducing the expression levels of _TPS21_ may lead to more FPP flowing into the dendrohine biosynthetic pathway. Similarly, increased _SQS2_ expression levels may also lead to more FPP flowing to the dendrohine biosynthesis pathway. After the treatment of _D. noble_ by MeJA or the mycorrhizal fungus MF23, _SQS2_ and _TPS21_ may directly or indirectly affect the biosynthesis of dendrohine. In the polysaccharide synthesis pathway, a total of 99 genes were found to be regulated by TFs after the treatment of _D.