title: Xanthomonas campestris cell-cell signalling molecule DSF (diffusible signal factor) elicits innate immunity in plants and is suppressed by the exopolysaccharide xanthan.
abstract: Several secreted and surface-associated conserved microbial molecules are recognized by the host to mount the defence response. One such evolutionarily well-conserved bacterial process is the production of cell-cell signalling molecules which regulate production of multiple virulence functions by a process known as quorum sensing. Here it is shown that a bacterial fatty acid cell-cell signalling molecule, DSF (diffusible signal factor), elicits innate immunity in plants. The DSF family of signalling molecules are highly conserved among many phytopathogenic bacteria belonging to the genus Xanthomonas as well as in opportunistic animal pathogens. Using Arabidopsis, Nicotiana benthamiana, and rice as model systems, it is shown that DSF induces a hypersensitivity reaction (HR)-like response, programmed cell death, the accumulation of autofluorescent compounds, hydrogen peroxide production, and the expression of the PATHOGENESIS-RELATED1 (PR-1) gene. Furthermore, production of the DSF signalling molecule in Pseudomonas syringae, a non-DSF-producing plant pathogen, induces the innate immune response in the N. benthamiana host plant and also affects pathogen growth. By pre- and co-inoculation of DSF, it was demonstrated that the DSF-induced plant defence reduces disease severity and pathogen growth in the host plant. In this study, it was further demonstrated that wild-type Xanthomonas campestris suppresses the DSF-induced innate immunity by secreting xanthan, the main component of extracellular polysaccharide. The results indicate that plants have evolved to recognize a widely conserved bacterial communication system and may have played a role in the co-evolution of host recognition of the pathogen and the communication machinery.
authors.affiliation: Centre for DNA Fingerprinting and Diagnostics, Nampally, Hyderabad 500001, India Graduate studies, Manipal University, Manipal, India.
authors.forename: Akanksha
authors.initials: A
authors.lastname: Kakkar
authors.affiliation: Centre for DNA Fingerprinting and Diagnostics, Nampally, Hyderabad 500001, India.
authors.forename: Narasimha Rao
authors.initials: NR
authors.lastname: Nizampatnam
authors.affiliation: Centre for DNA Fingerprinting and Diagnostics, Nampally, Hyderabad 500001, India.
authors.forename: Anil
authors.initials: A
authors.lastname: Kondreddy
authors.affiliation: Centre for DNA Fingerprinting and Diagnostics, Nampally, Hyderabad 500001, India.
authors.forename: Binod Bihari
authors.initials: BB
authors.lastname: Pradhan
authors.affiliation: Centre for DNA Fingerprinting and Diagnostics, Nampally, Hyderabad 500001, India subhadeep@cdfd.org.in.
authors.forename: Subhadeep
authors.initials: S
authors.lastname: Chatterjee
mesh_terms: D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology; D057865:Plant Immunity; D011135:Polysaccharides, Bacterial / Q000378:metabolism*; D015398:Signal Transduction; D014026:Nicotiana / Q000276:immunology* / Q000382:microbiology; D016959:Xanthomonas campestris / Q000235:genetics* / Q000378:metabolism
chemical_list: D011135:Polysaccharides, Bacterial; C002563:xanthan gum
keywords: Defence suppressor; Nicotiana benthamiana; Xanthomonas campestris pv. campestris; Xanthomonas oryzae pv. oryzae.; elicitor; extracellular polysaccharide; innate immunity; quorum sensing; rice; virulence