RNA Sequencing Reveals that Endoplasmic Reticulum Stress and Disruption of Membrane Integrity Underlie Dimethyl Trisulfide Toxicity against Fusarium oxysporum f. sp. cubense Tropical Race 4

Abstract

Fusarium wilt of banana, a destructive disease that affects banana production, is caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4). In a previous study, we confirmed the strong inhibitory effects of Chinese leek (Allium tuberosum) on the incidence of this disease. Sulfur compounds are the primary antifungal constituents of Chinese leek. Among these, dimethyl trisulfide (DT) was the most abundant and exhibited the strongest inhibition of Foc TR4 growth and development. In the present study, the global gene expression profiles of Foc TR4 isolates treated with DT at 4,000-folds dilution (concentration of 1/4,000, v/v) for 1.5, 6, and 12 h were investigated by using RNA sequencing. The expression patterns of 15 DEGs were validated based on quantitative real-time PCR (qRT-PCR) assay. Untreated sample presented 2,556, 1,691, and 1,150 differentially expressed genes (DEGs) at 1.5, 6, and 12 h after the onset of the experiment, respectively, whereas DT-treated isolates presented 2,823, 3,546, and 6,197 DEGs. Based on Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, DEGs involved in endoplasmic reticulum (ER), glycosylation, and steroid biosynthesis were significantly inhibited by DT exposure. The similar expressional patterns of 15 DEGs between RNA-seq and qRT-PCR assays indicated the reliability of the RNA-seq data. In conclusion, ER stress related to glycosylation inhibition and damage to cell membrane integrity might contribute to the toxicity of DT against Foc TR4. As the results presented here evidenced changes in gene expression associated with DT exposure, which might be used to develop new approaches for controlling FWB.

Keywords: Dimethyl trisulfide (DT); Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4); endoplasmic reticulum (ER) stress; steroid biosynthesis; target sites.

FIGURE 1

Changes in Foc TR4 viability induced by DT exposure. Conidia from control and treated isolates were incubated with FDA dye and their viability was assessed using a multifunctional microplate reader. Asterisks indicate a significant difference from the control, at ^∗P < 0.05, and ^∗∗P < 0.01.

FIGURE 2

Number of DEGs, which were up- and down-regulated in control and treated groups.

FIGURE 3

Gene Ontology classification analysis of DEGs. GO terms for which the false discovery rate (FDR) value was lower than 0.05 are listed.

FIGURE 4

The six most enriched DEGs pathways in each sample. Asterisks indicate the pathways for which the FDR value was lower than 0.05.

FIGURE 5

Expression profiles of ER-related genes.

FIGURE 6

Expression profiles of steroid biosynthesis-related genes. In the heatmap, (A–C) represent 1.5-C, 6-C, and 12-C (controls after 1.5, 6, and 12 h of incubation), and (D–F) represent 1.5-T, 6-T, and 12-T (treated samples after 1.5, 6, and 12 h of DT exposure), respectively.

FIGURE 7

Quantitative real-time PCR validation of candidate genes in enriched GO terms and pathways. Genes involved in: endocytosis, FOIG_02195, FOIG_00414, FOIG_13609, and FOIG_02810; oxidative phosphorylation, FOIG_06064; steroid biosynthesis, FOIG_07540, FOIG_08157, FOIG_12358, andFOIG_15550; and ER, FOIG_05398, FOIG_08856, FOIG_14848, and FOIG_16063.

FIGURE 8

Model illustrating the main molecular mechanism of the response of Foc TR4 to DT.