## 2 Results
### UDP-Dependent Glycosyltransferase(UGT) Gene  
UDP-dependent glycosyltransferases (UGTs) are pivotal in the process of glycosylation for decorating iridoid glycoside and phenylethanolamineoid glycosides with sugars. Phenylpropanoids are usually glycosylated at the 3-O or 7-O position, which serves to increase stability and solubility, as well as decrease the potential toxicity of the aglycone precursor [23]. UGTs belong to the largest family (Family 1) of the glycosyltransferase superfamily, and in _Arabidopsis thaliana_, more than 100 UGTs encoding genes have been identified [24; 25].  
In this research, a total of 325 UGTs were found in the _R. glutinosa_ transcriptome. Comparative transcriptome analysis revealed that 32, 25, 12, and 9 unigenes were differentially expressed in non-radial striations compared with radial striations in 1706, BJ1, QH1, and W85. Among them, 27, 23, 11, and 9 were upregulated genes, and only several genes were downregulated. Three members of UGT genes, including _CL3773.Contig3_, _CL5268.Contig2_, and _Unigene12367_, were upregulated in non-radial  
Figure 7: Expression patterns of acteoside biosynthetic unigenes between radial striations and non-radial striations of _R. glutinosa_. (**A**) Biosynthetic pathway of acteoside. The blue arrows indicate the tyrosine-derived pathway, and the purple arrows indicate the phenylalanine-derived pathway. The solid arrows denote known steps and the dashed arrows denote hypothetical steps. (**B**) Expression levels of the identified unigenes were annotated as enzyme coding genes from acteoside biosynthesis pathways. (**C**) Expression levels of unigenes involved in the biosynthesis of acteoside. Vertical bars indicate the standard deviation of three biological replicates. * indicate a significant difference at the \(p\) < 0.05 level. Abbreviations: PAL: phenylalanine ammonia-lyase; C4H, cinnamate-4-hydroxylase; C3H, coumarate-3-hydroxylase; TyDC, tyrosine decarboxylase; PPO, polyphenol oxidase; CuAO, copper-containing amine oxidase; ALDH, alcohol dehydrogenase; UGT, UDP-glucose glucosyltransferase; 4 CL, 4-comarate-CoA ligase; HCT, Shikimate _O_-hydroxycinnamoyltransferase.  
striations for every cultivar (Table S10, Figure 8A). Using the deduced amino acid sequences of the 18 _R. glutinosa_ UGT genes, multiple amino acid sequence alignment was conducted. The sequence alignment indicated that there is a conserved domain with the sequence of WAP-H-GWNS-E-DQ (Figure S5), which has been reported as a binding domain. Interestingly, homologous comparison analysis found that some UGT genes possessed higher sequence similarities and shared similar expression patterns (Figure 8B). For example, _CL10318.Contig4_ (UGT85A2) and _CL11397.Contig2_ (UGT85A1) were clustered into the same group, their expression was significantly upregulated in the non-radial striation of BJ1, and their Log2 Ratio(nRS/RS) values were greater than 1 in QH1 (Table S10). The qRT-PCR analysis indicated that _CL10318.Contig4_ and _CL11397.Contig2_ have extremely similar expression patterns in detected tissues (Figure 8C). It can be seen from the transcriptome and qRT-PCR analysis that most of the differentially expressed UGT genes showed higher expression levels in non-radial striations of _R. glutinosa_ tuberous roots, which provides strong evidence of the molecular mechanisms of active component accumulation.  
Figure 8: Expression patterns of UGTs between radial striations and non-radial striations of _R. glutinosa_. **(A)** Heat map representing expression dynamics of unigenes belongs to UGT encoding genes. **(B)** Phylogenetic tree of UGT proteins was generated by the neighbor-joining method using software of MEGA 6.0. **(C)** Relative expression levels of four UGT genes in radial striation and non-radial striation from 1706, BJ1, QH1, and W85 by qRT-PCR. Vertical bars indicate the standard deviation of three biological replicates. * indicate a significant difference at the \(p\) < 0.05 level.