Abstract
Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of rice blight disease as well as a serious phytopathogen worldwide. It is also one of the model organisms for studying bacteria-plant interactions. Current progress in bacterial signal transduction pathways has identified cyclic di-GMP as a major second messenger molecule in controlling Xanthomonas pathogenicity. However, it still remains largely unclear how c-di-GMP regulates the secretion of bacterial virulence factors in Xoo. In this study, we focused on the important roles played by DgcA (XOO3988), one of our previously identified diguanylate cyclases in Xoo, through further investigating the phenotypes of several dgcA-related mutants, namely, the dgcA-knockout mutant ΔdgcA, the dgcA overexpression strain OdgcA, the dgcA complemented strain CdgcA and the wild-type strain. The results showed that dgcA negatively affected virulence, EPS production, bacterial autoaggregation and motility, but positively triggered biofilm formation via modulating the intracellular c-di-GMP levels. RNA-seq data further identified 349 differentially expressed genes controlled by DgcA, providing a foundation for a more solid understanding of the signal transduction pathways in Xoo. Collectively, the present study highlights DgcA as a major regulator of Xoo virulence, and can serve as a potential target for preventing rice blight diseases.
Highlights
Xanthomonas oryzae pv. oryzae (Xoo) belongs to the gamma subdivision of Gram-negative proteobacteria with a single polar flagellum[1,2]
Our findings strongly suggest that the c-di-guanosine monophosphate (GMP) level in Xoo is significantly affected by dgcA, which seems to serve as a major regulator in controlling bacterial signal transduction and pathogenicity in Xoo
The importance of c-di-GMP in bacterial physiology has been well investigated to date, and a large number of diguanylate cyclases (DGCs) containing the conserved GGDEF domain were discovered in most bacterial strains[10,26]
Summary
Xanthomonas oryzae pv. oryzae (Xoo) belongs to the gamma subdivision of Gram-negative proteobacteria with a single polar flagellum[1,2]. Oryzae (Xoo) belongs to the gamma subdivision of Gram-negative proteobacteria with a single polar flagellum[1,2] It is a serious phytopathogen causing one of the most devastating diseases in rice— bacterial leaf blight[1,3], which has been estimated to incur as much as 50% economic loss of the annual rice yields worldwide[4]. Cyclic di-GMP [(bis-(3′–5′)-cyclic di-guanosine monophosphate)] is a ubiquitous second messenger that has been found to extensively involve in regulating a wide range of bacterial physiological functions[6,7] It is synthesized from two molecules of GTP by diguanylate cyclases (DGCs) containing the GGDEF domain, and hydrolyzed by phosphodiesterases (PDEs) containing either an EAL or HD-GYP domain to generate linear dinucleotide pGpG or guanosine monophosphate (GMP), respectively[7]. Different rice cultivars exhibit different degrees of pathogenicities because some of the rice plants like Zhonghua 11 may carry the elicitor-specific resistance genes that confer some degree of resistance to rice blast[18,19,20]
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