## 3 Results
### Metabolic Pathways Enrichment Analysis  
To investigate the different ways in which _R. chrysanthum_ responds to UV-B stress, KEGG pathway enrichment analysis was performed on DMs from the three comparator groups. The was a total of 22 DMs (9 up-regulated and 13 down-regulated) from the NvsM comparator group, which were mainly enriched in Alanine, aspartate, and glutamate metabolism; Glyoxylate and dicarboxylate metabolism; Glycine, Serine, and threonine metabolism (Figure 7A). The 34 DMs (22 up-regulated and 11 down-regulated) produced by the QvsN comparator group were mainly enriched in Cysteine and methionine metabolism; starch and sucrose metabolism; and Neomycin, kanamycin, and gentamicin biosynthesis (Figure 7B). A total of 38 DMs (26 up-regulated and 12 down-regulated) from the QvsM comparison group were mainly enriched in Alanine, aspartate, Cysteine and methionine metabolism; Tyrosine metabolism; and other metabolic pathways (Figure 7C).  
To comprehensively explore the metabolite metabolic network pathways of _R. chrysanthum_ under UV-B radiation, KEGG-enriched pathways were analyzed in 54 DMs after the deletion of duplicate DMs from the three comparison groups. Overall, UV-B stress mainly affected amino acid metabolic pathways in the two forms of _R. chrysanthum_, such as Alanine, aspartate, and glutamate metabolism; Cysteine and methionine metabolism; Glycine, Serine, and threonine metabolism; and Tyrosine metabolism. Carbohydrate pathway metabolism, such as Pentose and glucuronate interconversions, and starch and sucrose metabolism were also affected to some extent (Table 2). Changes in these metabolic pathways are closely related to nitrogen and carbohydrate metabolism, suggesting that _R. chrysanthum_ may respond to the stress effects of UV-B through alterations in carbon fixation pathways.  
Finally, we constructed the metabolic reprogramming network of _R. chrysanthum_ under UV-B stress. The results indicate that UV-B radiation promotes the production of the important intermediate carrier fumarate in the TCA cycle as well as increases the content of gamma-Aminobutyric acid, a positive response to abiotic stress, L-Asparagine, and N-Acetyl-L-asparatic acid as UV-B-responsive metabolites, all in a positive regulatory manner in response to UV-B stress (Figure 7D).  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**DMS Type** & **Class** & **Name** & **KEGG ID** & \(p\) **Value** & **FC** & **Type** \\ \hline \multirow{10}{*}{UV-B-responsive metabolites} & Fatty Acids & Palmitoleic acid & C08362 & 0.007 & 0.466 & down \\  & Fatty Acids & Myristoleic acid & C08322 & 0.02 & 2.057 & up \\  & Hormone & Normetanephrine & C05589 & 0.028 & 2.103 & up \\  & Indoles & Indoleacetic acid & C00954 & 0.00053 & 0.288 & down \\  & Lipids & Phytol & C01389 & 0.0026 & 0.52 & down \\  & Lipids & Cortisol & C00735 & 0.036 & 1.563 & up \\  & Lipids & MG182 & NA & 0.075 & 2.398 & up \\  & Nucleotide & Uridine & C00299 & 0.026 & 16.377 & up \\  & Nucleotide & Guanine & C00242 & 0.074 & 0.394 & down \\  & Vitamin & Alpha-Tocopherol & C02477 & 0.096 & 2.113 & up \\  & Organic Acids & Fumaric acid & C00122 & 0.033 & 1.57 & up \\  & Organic Acids & Maleic acid & C01384 & 0.035 & 1.91 & up \\  & Organic Acids & 3-Pyridylacetic acid & NA & 0.048 & 1.963 & up \\  & Organic Acids & 3-Hydroxybutyric acid & C01089 & 0.09 & 5.289 & up \\ \hline Potential UV-B stress biomarker & Organic Acids & Glyceric acid & C00258 & 0.0078 & 1.833 & up \\ \hline \end{tabular}
\end{table}
Table 1: _Cont._Figure 7: _Cont_.  
Figure 7: (**A**) Bubble plots of KEGG enrichment analysis of DMs in the NM group. (**B**) Bubble plots of KEGG enrichment analysis of DMs in the QN group. (**C**) Bubble plots of KEGG enrichment analysis of DMs in the QM group. (**D**) The simplified metabolic model based on a heatmap of DMs. The DMs changes were represented by the log2 FC. The color of the border indicated the shift in expression of the corresponding DMs, with red indicating up-regulation and green indicating down-regulation.