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. 2018 Oct 4:9:2280.
doi: 10.3389/fmicb.2018.02280. eCollection 2018.

Melatonin Treatment Inhibits the Growth of Xanthomonas oryzae pv. oryzae

Xian Chen  1 , Cheng Sun  2 , Pedro Laborda  1 , Yancun Zhao  1 , Ian Palmer  3 , Zheng Qing Fu  3 , Jingping Qiu  4 , Fengquan Liu  1
Affiliations

Melatonin Treatment Inhibits the Growth of Xanthomonas oryzae pv. oryzae

Xian Chen et al. Front Microbiol. .

Abstract

Xanthomonas oryzae pv. oryzae (Xoo) causes rice bacterial blight (BB), one of the most widespread and destructive diseases in rice-growing regions worldwide. Melatonin enhances pathogen resistance by inducing plant innate immunity, but the direct effect of melatonin on plant pathogenic bacteria is poorly understood. In this study, we investigated the direct effects of melatonin on Xoo. Exogenous melatonin at 200 μg/mL significantly inhibited the proliferation of Xoo and reduced the mRNA expression of five genes involved in cell division. This concentration of melatonin also inhibited the motility and biofilm formation of Xoo. Notably, melatonin was observed to alter the length of Xoo cells. To provide deeper insights into the mechanisms underlying this antibacterial activity, we examined global gene expression changes in Xoo strain PXO99 in response to the application of 200 μg/mL melatonin using RNA sequencing (RNA-Seq). A wide range of differentially expressed genes (DEGs) related to catalytic activity and metal-binding activity were downregulated in Xoo cells in response to the melatonin treatment. In addition, DEGs responsible for carbohydrate and amino acid metabolism were also downregulated. These results suggest that the inhibitory mechanism of melatonin on Xoo proliferation may involve the regulation of cell division in combination with a reduction in the concentration or activity of enzymes involved in metabolism.

Keywords: Xanthomonas oryzae pv. oryzae; antibacterial action; growth; melatonin; transcriptome.

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Figures

FIGURE 1
FIGURE 1
Melatonin inhibits the growth of Xoo. (A) The state of PXO99 under melatonin treatment. (B) Statistical analysis of growth curves of PXO99 treated with different concentrations of melatonin (μg/mL) and cultured for 24 h.
FIGURE 2
FIGURE 2
Statistical analysis of the swimming motility (A) and biofilm formation of Xoo (B) treated with melatonin. ∗P < 0.05, ∗∗∗P < 0.001.
FIGURE 3
FIGURE 3
Extraction and identification of melatonin in Xoo. (A) Chromatogram corresponding to melatonin. (a) Chromatogram corresponding to melatonin collected from PXO99 cells not treated with melatonin (Sigma). (b) Chromatogram corresponding to melatonin collected from PXO99 cells pre-treated with melatonin (Sigma). (B) Statistical analysis of melatonin (ng/cells) from PXO99 cells. UV response: 280 nm. ∗∗∗P < 0.001.
FIGURE 4
FIGURE 4
qRT-PCR analysis of the mRNA expression of cell-division-related genes in Xoo treated with melatonin. ∗∗∗P < 0.001.
FIGURE 5
FIGURE 5
Observations of Xoo morphology following treatment with melatonin. (A) The morphology of PXO99 cells. (a) The morphology of PXO99 cells not treated with melatonin. (b) The morphology of PXO99 cells treated with melatonin (200 μg/mL). (B) Statistical analysis of the width and length of PXO99 cells. Bar = 0.5 μm.
FIGURE 6
FIGURE 6
Classification of differentially expressed genes by gene ontology (GO) enrichment and cellular mapping. (A) Number of differentially expressed genes. (B) Cellular component classifications. (C) Molecular function. (D) Biological process.
FIGURE 7
FIGURE 7
Validation of 18 differentially expressed genes at the mRNA level by qRT-PCR.
FIGURE 8
FIGURE 8
Classification of differential genes in the metabolism in PXO99 under melatonin treatment.
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