3.1. Spatial Influence on L. aurea Bulbs Metabolome
We analyzed the metabolomes of 70% methanolic extracts from L. aurea bulbs across 15 samples from 5 geographical locations in China, identifying 731 metabolites (Table S1). These included 36.11% Alkaloids, 9.3% Flavonoids, 5.75% Lignans and Coumarins, 18.19% Phenolic acids, 1.92% Quinones, 12.59% Terpenoids, and 16.14% other compounds (Fig. 2A). OPLS-DA analysis (Fig. S1) effectively discriminated groups based on measured features, with strong predictive ability (Q²) and excellent model fit (R²), identifying 546 differential accumulated metabolites (DAMs) with VIP > 1 and |Log2FC| ≥ 1.0 (Table S2). 3D PCA (Fig. 2B) showed significant variance among groups, with biological replicates clustering closely. The hierarchical clustered heat map (Fig. 2C) confirmed differential metabolite abundance and identified biologically relevant pathways. These findings suggest location-specific differences in the metabolomic profiles of L. aurea bulbs, potentially influenced by environmental or genetic factors.
Table 1
Summary of DAMs across different compared groups.
| Group name | All significant differences | Down-regulated | Up-regulated |
| GX_vs_HN | 171 | 120 | 51 |
| GX_vs_JX | 238 | 161 | 77 |
| GX_vs_ZJ | 283 | 211 | 72 |
| HN_vs_JX | 229 | 115 | 114 |
| HN_vs_ZJ | 216 | 160 | 56 |
| JX_vs_ZJ | 298 | 208 | 90 |
| SC_vs_GX | 203 | 104 | 99 |
| SC_vs_HN | 211 | 146 | 65 |
| SC_vs_JX | 226 | 156 | 70 |
| SC_vs_ZJ | 319 | 244 | 75 |
The fold change (FC) values of metabolites in the comparison group were calculated to highlight metabolic differences, with the top 10 up-regulated and down-regulated metabolites presented in a dynamic distribution diagram (Fig. S2). FC values across groups were compared, and bar charts of the top 20 metabolites with the highest FC between groups indicated that L. aurea bulb metabolites decrease with lower altitude and latitude but increase with higher longitude (Fig. S3). A clustering heatmap of differential metabolites revealed that samples from lower altitude/latitude or higher longitude (HN, JX, ZJ) exhibited higher Z-scores in Alkaloids, Terpenoids, and Flavonoids compared to SC or GX (Fig. S4). GX vs JX showed higher Z-scores in Phenolic acids, Flavonoids, Lignans, and Coumarins.
UV scaling followed by K-means cluster analysis showed the trend of the relative content of differential metabolites in different groups in two subclasses. In subclass 1, 259 metabolites were ranked in the following order of abundance ZJ > HN > GX > JX > SC, clearly influenced by the altitude (Fig. S5A). In subclass 2, however, the order for the remaining 721 metabolites was JX > HN > SC > GX > ZJ (Fig. S5B). This result showed that geographic location and altitude do not necessarily predict cluster similarity, indicating that local environmental factors may outweigh simple spatial distance in shaping phenotypic or molecular traits. However, the Venn diagram analysis of the DAM showed the highest number of common DAM when ZJ was compared to others (Fig. S6D), but the lowest number of common DAM was when GX was compared to others (Fig. S6A).
The KEGG analysis revealed several significantly enriched (p < 0.05) DAM-associated metabolic pathways across the compared groups. However, after multiple comparison corrections, only the Flavonoid Biosynthesis (KO00941) pathway (P = 0.017, cluster frequency 42.86%) in the GX_vs_HN comparison and the Phenylpropanoid Biosynthesis (KO00940) pathway (P = 0.028, cluster frequency 25%) in the SC_vs_JX comparison remained significant (Table S3).
3.2. Spatial Influence on L. aurea Bulbs Gene Expression
Transcriptome sequencing of 15 samples from 5 locations generated 103.42 Gb of clean data, with each sample producing at least 6 Gb of clean reads and Q30 base percentages over 93%, indicating high sequencing quality. The assembly yielded a database of 189,456 unigenes with an average length of 1,060 bp, N50 of 1,478 bp, and N90 of 488 bp. Alignment with KEGG, NR, Swiss-Prot, GO, COG/KOG, and Trembl identified 77,301, 102,320, 73,923, 88,317, 62,084, and 101,653 homologs, covering 40.8%, 54.01%, 39.02%, 46.62%, 32.77%, and 53.66% of the sequences, respectively (Fig. 4A). Pfam comparison revealed 54,940 homologs with 29% coverage, and NR BLAST hits showed a 48.06% match with Asparagus officinalis (Fig. 4B). GO classification revealed enriched terms in biological process (cellular process, metabolic process, response to stimulus), cellular component (cellular anatomical entity, protein-containing complex), and molecular function [binding, catalytic activity, ATP (Adenosine triphosphate)-dependent activity] (Fig. 4C). KOG analysis categorized unigenes into 25 functional classes, with the largest group being "general function prediction only" (R, 14,692 unigenes), followed by "translation, ribosomal structure and biogenesis" (J, 7,163 unigenes), and "function unknown" (S, 5,536 unigenes), along with categories such as "posttranslational modification" (O), "transcription" (K), and "replication, recombination and repair" (L) (Fig. 4D).
FPKM analysis revealed 60600 DEGs with |log2Fold Change| >= 1 and FDR < 0.05 (Table 2) (Table S4). There was a significant difference in up-and down-regulated genes between groups, suggesting a location-specific difference in the L. aurea gene expression.
Table 2
Summary of DEGs across different compared groups.
| Group name | All significant differences | Down-regulated | Up-regulated |
| GX_vs_HN | 11253 | 5619 | 5634 |
| GX_vs_JX | 23871 | 12569 | 11302 |
| GX_vs_ZJ | 20792 | 9468 | 11324 |
| HN_vs_JX | 22693 | 11686 | 11007 |
| HN_vs_ZJ | 20763 | 9288 | 11475 |
| JX_vs_ZJ | 27933 | 12232 | 15701 |
| SC_vs_GX | 15376 | 8337 | 7039 |
| SC_vs_HN | 17867 | 9593 | 8274 |
| SC_vs_JX | 27846 | 15503 | 12343 |
| SC_vs_ZJ | 24879 | 12166 | 12713 |
The FPKM distribution box plot showed consistent gene expression with narrow IQRs in the ZJ, JX, HN, and GX groups (Fig. S7A). In contrast, the SC group displayed greater variability and a wider IQR, indicating gene expression fluctuation. This was further confirmed by the FPKM density distribution (Fig. S7B) and violin plot (Fig. S7C). Pearson correlation analysis (Fig. 4A) revealed strong consistency in gene expression within most groups, especially ZJ, JX, HN, and GX, while SC showed weaker correlations, indicating higher variability. 3D PCA analysis (Fig. 4B) showed that PC1 (19.41%), PC2 (15.09%), and PC3 (12.76%) captured significant variance, with distinct clustering of ZJ and JX, overlap in SC and GX, and separation of the HN group.
The volcano plots (Fig. S8) revealed that most clusters were non-regulated across comparisons, with several key clusters showing significant upregulation or downregulation, particularly in the order JX_vs_ZJ > SC_vs_JX > SC_vs_ZJ > GX_vs_JX. The highest number of significantly up-regulated genes was observed in the JX_vs_ZJ comparison (15,701). The SC group exhibited a higher proportion of non-regulated genes, especially in the SC_vs_GX (45,224) and SC_vs_ZJ (35,721) comparisons. The radar chart (Fig. S9) identified clusters with substantial fold changes between comparisons. In the JX_vs_ZJ comparison, clusters such as 92568.3 and 90745.2 showed significant fold changes, while in SC_vs_JX, clusters 90372.1 and 63903.15 were notable. Similarly, in SC_vs_ZJ, clusters 50696.3 and 93131.15 exhibited large fold changes, and in GX_vs_JX, clusters 93131.19 and 63903.15 were significantly changed. Notably, cluster 90372.1 appeared in six comparisons (GX_vs_JX, GX_vs_ZJ, HN_vs_JX, HN_vs_ZJ, SC_vs_JX, and SC_vs_ZJ), and cluster 51222.2 was found in four comparisons (GX_vs_JX, GX_vs_ZJ, SC_vs_JX, and SC_vs_ZJ). Several other top clusters were also common across two or three comparisons.
The heatmap color bar and hierarchical clustering dendrogram between groups (Fig. S10) showed distinct gene expression patterns between L. aurea bulbs from different locations, with clear group separation. Some genes varied within the same group, suggesting environmental or genetic influences. Clustering revealed that SC was most closely related to GX, followed by ZJ, HN, and JX (Fig. 5).
K-means cluster analysis of 60,600 DEGs revealed distinct gene expression patterns across 10 subclasses (Fig. S11). In subclass 1, 7,005 DEGs were ranked in the order ZJ > JX > HN > GX > SC (Fig. S11A), while in subclass 2, 8,501 DEGs were ranked SC > GX > HN > JX > ZJ (Fig. S11B), indicating altitude influence. Sharp peaks in subclasses 3, 5, and 6 (Fig. S11C, E, F) were observed in HN; ZJ and SC in subclass 4 (Fig. S11D); GX in subclasses 7 and 8 (Fig. S11G, H); and JX in subclasses 9 and 10 (Fig. S11I, J), suggesting environmental or other factors. The Venn diagram showed the highest number of unique DEGs in JX compared to other groups (Fig. S12C), while GX had the fewest unique DEGs (Fig. S12A).
KEGG analysis of DEGs identified several significant DEG-associated pathways (p < 0.05) across the compared groups, with 10 pathways remaining significant after P-value adjustment (Table S5). The Protein processing in endoplasmic reticulum pathway (KO04141) was significant in SC_vs_JX (P = 0.0000003901), HN_vs_ZJ (P = 0.0000008429), GX_vs_HN (P = 0.0000074452), SC_vs_HN (P = 0.0000490227), JX_vs_ZJ (P = 0.0000816909), HN_vs_JX (P = 0.0002185169), GX_vs_JX (P = 0.0085480832), and SC_vs_ZJ (P = 0.0091569183). The Ribosome pathway (KO03010) was significant in SC_vs_HN (P = 0.0000039810) and HN_vs_ZJ (P = 0.0001579419). The Starch and sucrose metabolism pathway (KO00500) was significant in SC_vs_GX (P = 0.0067584993) and GX_vs_JX (P = 0.0113422941). The Cutin, suberine, and wax biosynthesis pathway (KO00073) was significant in SC_vs_GX (P = 0.0004739915) and SC_vs_ZJ (P = 0.0195882035). Other significant pathways included the Spliceosome pathway (KO03040) in HN_vs_ZJ (P = 0.0000519557), Biosynthesis of secondary metabolites (KO01110) in SC_vs_ZJ (P = 0.0096887642), Biosynthesis of unsaturated fatty acids (KO01040) in SC_vs_HN (P = 0.0066542895), Phenylpropanoid biosynthesis (KO00940) in JX_vs_ZJ (P = 0.0037528038), Linoleic acid metabolism (KO00591) in GX_vs_HN (P = 0.0002745666), and Glutathione metabolism (KO00480) in GX_vs_ZJ (P = 0.0199734744).
3.3. Integrated Analysis
Combined PCA analysis of the transcriptome and metabolome showed distinct clustering of samples, particularly from ZJ and SC (Fig. 6A), with clear separation between regions, indicating unique gene expression profiles. Metabolome data (Fig. 6B) also revealed differentiation, with ZJ displaying a unique metabolic profile, while HN and GX clustered closely together. JX samples showed overlapping and distinct separation patterns, suggesting varying metabolic signatures. Overall, ZJ exhibited the most pronounced differences in both transcriptomic and metabolomic profiles.
A pearson correlation between the environmental variables and the K-means cluster analysis sub-classes of the DAMs and DEGs demonstrated a complex interplay between them (Fig. 7). Gene subclass 6 showed high (p < 0.001) positive correlation with Se concentration whereas metabolite subclass 1 showed moderate positive (p < 0.01) correlation with soil pH and week positive correlation (p < 0.05) with elevation. Gene subclass 1 showed a weak negative correlation (p < 0.05) with the highest temperature and longitude. The dendrogram showed that gene subclass 6 and metabolite subclass 2 are highly correlated and grouped. Metabolite subclass 1 and gene subclass 9 are highly correlated and grouped, which in turn are related to gene subclass 1.
Combined KEGG pathway analysis revealed that the top pathways containing more than five DAMs were: Metabolic pathways (KO01100), Biosynthesis of secondary metabolites (KO01110), Phenylpropanoid biosynthesis (KO00940), Tryptophan metabolism (KO00380), and Flavonoid biosynthesis (KO00941) (Fig. 8A, Table S6). The top pathways containing more than 100 DEGs were: Metabolic pathways (KO01100), Biosynthesis of secondary metabolites (KO01110), Biosynthesis of amino acids (KO01230), Biosynthesis of cofactors (KO01240), Phenylpropanoid biosynthesis (KO00940), Glycerophospholipid metabolism (KO00564), Tryptophan metabolism (KO00380), and Glutathione metabolism (KO00480) (Fig. 8A, Table S6). After enrichment analysis of DAMs, six KEGG pathways were identified; following P-value adjustment, only Flavonoid biosynthesis (KO00941) and Phenylpropanoid biosynthesis (KO00940) remained significant in GX_vs_HN and SC_vs_JX, respectively (Fig. 8B, Table S7). KEGG enrichment analysis of DEGs revealed twelve KEGG pathways, with only Phenylpropanoid biosynthesis (KO00940) and Biosynthesis of secondary metabolites (KO01110) remaining significant in JX_vs_ZJ and SC_vs_ZJ, respectively (Fig. 8B, Table S7).
The bar chart (A) displays the 25 pathways with the highest P-values in multi-omics analysis, where the bar length represents the number of differential metabolites and differential genes enriched in each pathway. The bubble diagram (B) shows the top 25 pathways with the highest P-values, where the X axis represents the enrichment factor, the bubble shape indicates DEGs or DAMs, with their size representing the number of genes or metabolites, and the color denotes the P-value. To analyze the regulatory network of DAMs, correlation analysis between DEGs and DAMs was performed in each group, revealing 67,962 DEGs significantly correlated with 732 DAMs (Table S8). Expression trend analysis showed that multiple metabolites were positively or negatively regulated by several genes (Fig. S13). For example, in GX_vs_HN (Fig. S13A), positive correlations between genes and metabolites were fewer compared to SC_vs_JX (Fig. S13B), JX_vs_ZJ (Fig. S13C), and SC_vs_ZJ (Fig. S13D). KGML analysis across groups revealed that the ath00010 pathway was the most highly clustered, followed by ath00260 and ath00030 in SC_vs_JX (Fig. S14B) and SC_vs_ZJ (Fig. S14D). In GX_vs_HN (Fig. S14A), the second most clustered pathway was ath00020, while in JX_vs_ZJ (Fig. S14C), it was ath00520. The ath00260 pathway was the most upregulated cluster in SC_vs_JX, JX_vs_ZJ, and SC_vs_ZJ. CCA analysis of genes and metabolites related to the KO00941 pathway in GX_vs_HN (Fig. S15A), KO00940 pathway in SC_vs_JX (Fig. S15B), KO01110 pathway in JX_vs_ZJ (Fig. S15C), and KO00940 pathway in SC_vs_ZJ (Fig. S15D) showed strong correlations. In GX_vs_HN, MWSHY0098 (Epigallocatechin), MWSHY0037 (Isoliquiritigenin*), and others were down-regulated, while MWS0178 [Chlorogenic acid (3-O-Caffeoylquinic acid)*] was up-regulated. In SC_vs_JX, MWS2212 (Caffeic acid), MWS0906 (Coniferin), and HJN003 (1-O-Sinapoyl-β-D-glucose) were up-regulated, while MWS2208 (Ferulic acid) and others were down-regulated. In SC_vs_ZJ, MWS2212, MWSHY0037, and MWS0178 were up-regulated, and other metabolites like MWS0677 (N-Acetyl-5-hydroxytryptamine) were down-regulated. MWS0178 was up-regulated in all but SC_vs_JX, indicating a positive correlation with latitude, while MWS2212 was inversely correlated with latitude. Gene clusters related to their regulation were identified. MWSHY0098 and MWSCX015 (Caffeic aldehyde) were influenced by longitude. Ten metabolites, such as LSKP211262 (Secoisolariciresinol), decreased with lower elevation, and four metabolites, including MW0139629 (Sakuranetin), decreased with increasing latitude and decreasing altitude, suggesting that latitude, altitude, and environmental factors affect L. aurea gene expression and metabolism.