Transcriptomic and sugar metabolic analysis reveals molecular mechanisms of peach gummosis in response to Neofusicoccum parvum infection

Abstract

Peach gummosis, a devastating disease caused by Neofusicoccum parvum, significantly shortens peach tree lifespan and reduces the yield of peach trees. Despite its impact, the molecular mechanism underlying this disease remains largely unexplored. In this study, we used RNA-seq, sugar metabolism measurements, and an integrated transcriptional and metabolomic analysis to uncover the molecular events driving peach gummosis. Our results revealed that N. parvum infection drastically altered the transcripts of cell wall degradation-related genes, the log₂Fold change in the transcript level of Prupe.1G088900 encoding xyloglucan endotransglycosylase decreased 2.6-fold, while Prupe.6G075100 encoding expansin increased by 2.58-fold at 12 hpi under N. parvum stress. Additionally, sugar content analysis revealed an increase in maltose, sucrose, L-rhamnose, and inositol levels in the early stages of infection, while D-galactose, D-glucose, D-fructose consistently declined as gummosis progressed. Key genes related to cell wall degradation and starch degradation, as well as UDP-sugar biosynthesis, were significantly upregulated in response to N. parvum. These findings suggest that N. parvum manipulates cell wall degradation and UDP-sugar-related genes to invade peach shoot cells, ultimately triggering gum secretion. Furthermore, weighted gene co-expression network analysis (WGCNA) identified two transcription factors, ERF027 and bZIP9, as central regulators in the downregulated and upregulated modules, respectively. Overall, this study enhances our understanding of the physiological and molecular responses of peach trees to N. parvum infection and provide valuable insights into the mechanisms of peach defense against biotic stresses.

Keywords: N. parvum; gummosis; peach; sugar metabolome; transcriptome.

Figure 1

Development of peach gummosis in current-year shoots inoculated with N. parvum strain JSZ01. (A) Morphological progression of gummosis in current-year shoots wounded and inoculated without (mock) or with N. Parvum. (B) Lesion diameter in infected shoots at different time points. Bar in graph A is 0.5 cm. Error bars represent ± SD (n = 3). Asterisks indicate significant differences between 12 hours post inoculation (hpi) and the each other time points (**P < 0.01, ***P < 0.001).

Figure 2

Transcriptomic analysis of peach shoots inoculated with Mock or N. Parvum at various time points. (A) Comparative analysis of differential expressed genes (DEGs) between mock (C) and N. parvum-inoculated (T) peach shoots at 12 h, 24 h, 36 h, 48 h, and 60 h. The numbers on the scatter diagram indicates the amount of DEGs. Up- and down-regulated DEGs are indicated with red and blue scatter, respectively. ‘T12 vs. C12’ indicates that the samples under N. Parvum infection treatment are compared with the mock at 12 h. (B) GO analysis of DEGs between different stages of mock and N. Parvum infection. The circle size indicted the DEGs count, and the circle color indicated q value. (C) DEGs involved in ‘xyloglucan metabolic process’ and ‘cell wall’ processes, indicating key genes related to cell wall modification and stress response.

Figure 3

Metabolome analysis of peach shoots inoculated with Mock or N. Parvum at various time points. (A) Heatmap depicting correlation coefficient of metabolites of all samples. (B) PCA score plot of metabolite data. Each point represents an independent biological replicate. (C) Number of differential metabolites in metabolome at different time points. The numbers on the histograms indicates the amount of differential metabolites. Up- and down-regulated metabolites are indicated with red and blue histograms respectively. (D) KEGG pathway annotation for the metabolite profiles related to N. Parvum inoculation reflection. The numbers on the histograms indicates the amount of differential sugar metabolites at different time points. (E) Heatmap of metabolites. The heatmap shows the metabolite content of all samples, with low to high levels represented by a gradient of green to red.

Figure 4

Expression profiles of structural genes and metabolites in the sugar metabolism pathway in mock and N. parvum-inoculated shoots. The heatmap shows the relative expression levels of structural genes on the basis of FPKM values, with low to high expression represented by a gradient of green to red. The metabolite levels are indicated by a blue and red color scheme, with blue representing low levels and red representing high levels.

Figure 5

Expression dynamics of differentially expressed transcription factors families from the transcriptome profile. (A) Classification statistics of differentially expressed transcription factors families. (B) Heatmap of 38 differentially expressed ethylene-responsive factors (ERFs).

Figure 6

Gene modules identified by WGCNA assay based on the transcriptome profile. (A) Gene dendrogram and module colors were obtained by WGCNA. The major tree branches constitute 5 modules, marked with different colors. Heatmap depicting module–sample correlation. The correlation network analysis of ERF027 and bZIP9 and their major co-expressed genes from the blue (B) and turquoise (C) modules.

Figure 7

Validation of transcriptome data by qPCR for genes related to pathogen stress. The histograms and Line charts indicate the RNA-seq and qPCR results of 12 DEGs respectively.