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. 2024 Oct 18;12(2):uhae300.
doi: 10.1093/hr/uhae300. eCollection 2025 Feb.

A transcription factor, PbWRKY24, contributes to russet skin formation in pear fruits by modulating lignin accumulation

Jialong Wang  1   2 , Dong Wang  1   2 , Mingrui Zhao  1   2 , Mengyuan Yu  1   2 , Xiaodong Zheng  1   2 , Yike Tian  1   2 , Zhijuan Sun  3 , Xiaoli Liu  1   2 , Caihong Wang  1   2 , Changqing Ma  1   2
Affiliations

A transcription factor, PbWRKY24, contributes to russet skin formation in pear fruits by modulating lignin accumulation

Jialong Wang et al. Hortic Res. .

Abstract

Skin color is one of the major traits of fruit appearance quality in pear (Pyrus) that affects the fruit commodity value. Russet skin protects pear fruits from environmental stresses and its formation process is closely linked to lignin accumulation. However, the molecular regulatory networks underlying russet skin formation in pear fruits involve complex secondary metabolic pathways and remain elusive. Here, we explored the regulatory mechanisms underlying lignin accumulation in pear skin based on transcriptome sequencing, co-expression network analysis, and gene expression profiling. We identified a WRKY transcription factor gene, PbWRKY24, that regulates russet skin formation in pear fruits. The relative expression of PbWRKY24 in russet pear skin was significantly correlated with lignin content. We then verified the function of PbWRKY24 in lignin accumulation via genetic transformation. DNA affinity purification sequencing revealed that PbWRKY24 directly binds to the promoter of a lignin biosynthesis gene, PbPRX4. This binding was confirmed by yeast one-hybrid, dual-luciferase, and electrophoretic mobility shift assays. Overexpression of PbPRX4 in pear skin stimulated lignin accumulation and consequently promoted russet skin formation. This study provides a glimpse into the intricate lignin biosynthesis mechanisms during russet skin formation in pear fruits, which is of practical significance to pear breeding for fruit quality.

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Conflict of interest statement

The authors declare that they have no conflicts of interest associated with this work.

Figures

Figure 1
Figure 1
Changes in skin color and pigment contents of pear fruits. (A) Color development, (B) Lignin content, and (C) Chlorophyll content in fruit skin from 50 to 125 DAFB. Bars represent standard error of the mean (n = 4). Different lower case letters indicate significant differences by Tukey’s multiple range test (P <0 .05).
Figure 2
Figure 2
Simplified schemes and expression heat maps of lignin biosynthesis-related structural genes and TF family genes in pear skin. (A) Structural genes. (B) TF family genes. R/N50, 75, and 125: russet/non-russet skin fruits at 50, 75, and 125 DAFB. Detail information of those genes was listed in Table S4.
Figure 3
Figure 3
WGCNA of DEGs identified in pear skin. (A) Hierarchical cluster tree displaying 13 modules of co-expressed genes. Tree leaves and branches represent the DEGs and modules, respectively. (B) Trait correlations and corresponding P-values for the 13 modules. (C) Cytoscape representation of co-expressed genes in the ‘Paleturquoise’ module. Member gene IDs and common names are given. (D) Heat map showing the expression patterns of co-expressed genes in the ‘Paleturquoise’ module. Detailed information of DEGs in the ‘Paleturquoise’ module is listed in Table S5.
Figure 4
Figure 4
Subcellular localization and gene expression of PbWRKY24 in pear fruit skin. (A) Color phenotypes, (B) lignin content, and (C) PbWRKY24 expression in pear skin of six different cultivars. (D) Microphotographs showing PbWRKY24-GFP fusion plasmid transient expression in epidermal cells of onion. (E) Skin phenotype, (F) PbWRKY24 expression, and (G) lignin content in fruits upon overexpression and silencing of the PbWRKY24 gene.
Figure 5
Figure 5
PbWRKY24 directly binds to the promoter of PbPRX4 and thereby enhances its transcription. (A) DNA-binding sites of PbWRKY24. (B) Visualization and analysis of PbPRX4 as a potential target gene of PbWRKY24. (C) Schematic diagram illustrating the distribution of W-box in the PbPRX4 promoter. (D) Y1H assay showing that PbWRKY24 binds to the PbPRX4 promoter. (E) EMSA assay showing that PbWRKY24 binds to the PbPRX4 promoter. (F) LUC activity assay showing that PbWRKY24 activates the PbPRX4 promoter. Data analysis of the relative firefly luciferase/Renilla luciferase (LUC/REN) ratio from transient expression assays in the figure.
Figure 6
Figure 6
Functional identification PbWRKY24 in transgenic tobacco plants. (A) Phenotype, (B) PbWRKY24 expression, (C) PRX4 expression, (D) lignin content, and (E) lignin staining and autofluorescence in stems of WT and PbWRKY24-overexpressing (PbWRKY24-OE) lines.
Figure 7
Figure 7
Overexpression and silencing of the PbPRX4 gene in pear fruit skin. (A) Skin phenotype. (B) PbPRX4 expression. (C) Lignin content.
Figure 8
Figure 8
Conceptual model for PbWRKY24 regulation of lignin accumulation in russet pear skin. PbWRKY24 modulates lignin biosynthesis pathway in russet fruit skin of pear by directly binding to the PbPRX4 promoter and activating PbPRX4 transcription.
See this image and copyright information in PMC

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