## 3 Results
### Bioinformatics Analysis  
To further clarify the evolutionary status of _ZbFPS_ amino acid sequences, a phylogenetic tree was established by the neighbor-joining method (we have clarified the bioinformatics analysis of _ZbDXS_ in previous studies) [22]. At the tip of the clade, the shorter branch length proves the vital amino acid conservation of its clustering genes and illustrates the close evolutionary relationship between members. The longer branch length indicates that its members evolve faster [27]. According to Figure 1, all plant FPS sequences were separated into three main groups. _ZbFPS_ was most closely related to _CcFPS_ (_Citrus clementina_) and _CsFPS_ (_Citrus sinensis_), both of which belong to the family Rutaceae. It was speculated that _Z. bungeanum_ and _citrus_ may be derived from the same ancestor. _Z. bungeanum_ had a faster evolutionary speed than _citrus_, and _citrus_ genes had more vital amino acid conservation than _Z. bungeanum_. At the same time, according to the relationship, _ZbFPS_ had a close kinship with _MiFPS_ (_Mangifera indica_), _DzFPS_ (_Durio zibethinus_), _RrFPS_ (_Rosa rugosa_), and _SgFPS_ (_Siraitia grosverovii_), which were primarily trees with pickles and aroma. The amino acid sequence of the phylogenetic tree was determined from NCBI. [PERSON] analyzed the protein information of _ZbFPS_, and the results were shown in Table S2. Prot Scale was used to predict the hydrophobicity/hydrophilicity of the amino acid sequences of _ZbFPS_ (Figure S4). For _ZbFPS_, position 309 of the polypeptide chain was the most hydrophilic with the lowest score of \(-\)2.867, and position 202 was the most hydrophobic with the highest score of 2.444. Overall, the distribution of hydrophilic amino acids was relatively uniform, and the number was more significant than that of hydrophobic amino acids. Therefore, it was speculated that the _ZbFPS_ protein was a hydrophilic protein. Prediction of the signal peptide of the amino acid sequence of _ZbFPS_ was made using Signal P 4.1 Server (Figure S4). Generally, the mean S value (mean S-score) was used to consider whether it was a secreted protein. The average value of S was more significant than 0.5, which was predicted to be a secreted protein and the presence of a signal peptide. Analysis results showed that _ZbFPS_ was not secreted by proteins. Plant-mPLoc and Euk-mPLoc 2.0 were used for subcellular localization of _ZbDXS_ and _ZbFPS_ (Figure S5). The results showed that _ZbDXS_ was most likely localized in chloroplast, and _ZbFPS_ was most likely localized in mitochondria. Under the influence of evolutionary forces, proteins form a 3D structure to meet specific functional needs. Therefore, understanding the tertiary structure of a protein can help us understand its function. However, it is time-consuming and laborious to determine the tertiary structure of the protein through experiments, and building a model through a computer can make it easier for us to understand the properties of the protein [28]. The predicted tertiary structures of _ZbDXS_ and _ZbFPS_ are shown in Figure 2. Human _DXS_ with 41.34% sequence identity served as a template for comparative modeling. The GMQE (Global Model Quality Estimation) was >0.63 (Table S3), and the QMEAN (Qualitative Model Energy ANalysis) was\(-\)-3.04 (Table S5). The 3D model for _ZbFPS_ was established based on the template of human _FPS_ (82.06% sequence identity). The GMQE was >0.96, indicating the high quality of the result, and the QMEAN was >-0.06 (Table S3). The predicted structures of _ZbDXS_ and _ZbFPS_ consisting predominantly of alpha-helices were folded as a single domain. Figure 1: Results of phylogenetic analysis of ZbFPS and other plants. The numbers in the figure represent the genetic distance. Bootstrap values are shown as a percentage of 1000 replicates. Different colors represent different clades. ZbFPS is marked by green dots.