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Figure 1. 

Phylogenetic tree of STP proteins based on multiple species. The outermost ring of the phylogenetic tree is color-coded to represent different subfamilies, while distinct symbols on the branches denote various species. The numbers above the branches indicate bootstrap values. The abbreviations At, Cs, Sl, Me, Br, Sb, and Vv correspond to Arabidopsis, sweet orange, tomato, cassava, Chinese cabbage, sorghum, and grape, respectively.

Figure 2. 

Chromosomal localization and intra-species synteny of MdSTPs gene family members in apple. (a) Illustrates the chromosomal localization of MdSTPs gene family members in apple. (b) Demonstrates the syntenic relationships within the apple genome. In (a), the positions of individual genes are marked by black lines, with corresponding chromosome numbers displayed at the top of each chromosomal bar. In (b), grey lines represent syntenic blocks within the apple genome, while black lines specifically indicate syntenic gene pairs of MdSTPs. The innermost first and second concentric circles display gene density distributions across corresponding chromosomes, presented as heatmaps and line graphs, respectively.

Figure 3. 

Gene structure of MdSTPs. Exons are depicted as yellow boxes, while introns are represented by black lines.

Figure 4. 

Analysis of motifs in MdSTPs Proteins. (a) A total of 10 motifs were identified. (b) Sequence characteristics of the motifs. In (a), the 10 putative motifs are sequentially numbered from 1 to 10 and represented by distinct colors.

Figure 5. 

Cis-acting regulatory elements of MdSTPs genes. A total of 27 cis-acting elements were identified within the promoter regions of the 30 MdSTPs genes, each represented by distinctively colored boxes.

Figure 6. 

Expression levels of MdSTPs across various cultivars and tissues. At the bottom of the heatmap, 'Variety' denotes different apple cultivars, while 'Organ' represents various tissue types. The heatmap employs a blue-yellow-red color gradient to indicate gene expression levels, ranging from low to high. The expression levels are comparatively analyzed based on the integrated data from both the horizontal and vertical axes.

Figure 7. 

The expression level of MdSTPs in fruits and its transcriptional regulatory mechanism. (a) Expression levels of MdSTPs in fruits. (b) Transcription factor regulatory network. (c) Correlation between the expression levels of MdERFs and MdSTPs. (d) Expression levels of MdERFs in fruits. In (a) and (d), '100 day' refers to 100 d post-flowering, while 'harvest' indicates the fruit ripening stage. The blue-white-red color gradient represents low-medium-high expression levels, respectively. The expression levels are comparatively analyzed based on the integrated data from both the horizontal and vertical axes. In (b), blue denotes transcription factors, while orange represents MdSTPs.

Figure 8. 

The molecular conformation of the docking between MdERF and MdSTP13 promoter region. The red dashed lines indicate hydrogen bonds between the AP2 domain and the MdSTP13 promoter region.

Figure 9. 

Expression levels of MdSTPs gene under different hormone treatments. The horizontal axis represents different time points of plant hormone treatments, while the vertical axis indicates the relative expression levels of MdSTPs. The blue-white-red color gradient signifies low-medium-high gene expression levels, respectively. The expression levels are comparatively analyzed based on the integrated data from both the horizontal and vertical axes.