Abstract
Xanthomonas oryzae pv. oryzae (Xoo), a causal agent of bacterial leaf blight of rice, possesses two-component regulatory systems (TCSs) as an intracellular signaling pathway. In this study, we observed changes in virulence, biofilm formation, motility, chemotaxis, and tolerance against oxidative stress of a knockout mutant strain for the PXO_RS20535 gene, encoding an orphan response regulator (RR). The mutant strain lost virulence, produced significantly less biofilm, and showed remarkably reduced motility in swimming, swarming, and twitching. Furthermore, the mutant strain lost glucose-guided movement and showed clear diminution of growth and survival in the presence of H2O2. These results indicate that the RR protein encoded in the PXO_RS20535 gene (or a TCS mediated by the protein) is closely involved in regulation of biofilm formation, all types of motility, chemotaxis, and tolerance against reactive oxygen species (ROS) in Xoo. Moreover we found that the expression of most genes required for a type six secretion system (T6SS) was decreased in the mutant, suggesting that lack of the RR gene most likely leads to defect of T6SS in Xoo.
Highlights
Xanthomonas oryzae pv. oryzae (Xoo) is a Gram-negative rod-shaped bacterium and one of the most common pathogens of rice [1]
Based on data set from the RNA-sequencing analysis, we investigated phenotypic changes and genes expression of the mutant strain to elucidate regulatory function of RR35 protein in
Rr35 in the genome is independent of other pil genes. These findings indicate that the RR35 protein either regulates Xoo pilus independently or has a different function from PilH of P. aeruginosa and Xanthomonas campestris pv. campestris (Xcc)
Summary
Xanthomonas oryzae pv. oryzae (Xoo) is a Gram-negative rod-shaped bacterium and one of the most common pathogens of rice [1]. Oryzae (Xoo) is a Gram-negative rod-shaped bacterium and one of the most common pathogens of rice [1]. Xoo is a vascular pathogen, invading rice plants through natural openings on leaves, hydathodes, or wounds [2]. Xoo multiplies in xylem and impedes water flow, resulting in drying of leaves. A disease caused by Xoo is bacterial leaf blight (BLB), which causes significant loss of potential rice yield worldwide [3]. This indicates the need for in-depth study of virulence mechanisms of the bacteria and efforts over the past decades have functionally characterized many of the virulence factors required for bacterial disease. The factors include diffusible signal factors (DSFs), extracellular polysaccharides (EPSs), lipopolysaccharides (LPSs), adhesins, motility factors, biofilm formation species, type 2 secretion system (T2SS), type 3 secretion system (T3SS), type 6 secretion system (T6SS), and extracellular enzymes [4,5,6,7,8,9,10,11,12]
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