title: Host plant peptides elicit a transcriptional response to control the Sinorhizobium meliloti cell cycle during symbiosis.
abstract: The α-proteobacterium Sinorhizobium meliloti establishes a chronic intracellular infection during the symbiosis with its legume hosts. Within specialized host cells, S. meliloti differentiates into highly polyploid, enlarged nitrogen-fixing bacteroids. This differentiation is driven by host cells through the production of defensin-like peptides called "nodule-specific cysteine-rich" (NCR) peptides. Recent research has shown that synthesized NCR peptides exhibit antimicrobial activity at high concentrations but cause bacterial endoreduplication at sublethal concentrations. We leveraged synchronized S. meliloti populations to determine how treatment with a sublethal NCR peptide affects the cell cycle and physiology of bacteria at the molecular level. We found that at sublethal levels a representative NCR peptide specifically blocks cell division and antagonizes Z-ring function. Gene-expression profiling revealed that the cell division block was produced, in part, through the substantial transcriptional response elicited by sublethal NCR treatment that affected ∼15% of the genome. Expression of critical cell-cycle regulators, including ctrA, and cell division genes, including genes required for Z-ring function, were greatly attenuated in NCR-treated cells. In addition, our experiments identified important symbiosis functions and stress responses that are induced by sublethal levels of NCR peptides and other antimicrobial peptides. Several of these stress-response pathways also are found in related α-proteobacterial pathogens and might be used by S. meliloti to sense host cues during infection. Our data suggest a model in which, in addition to provoking stress responses, NCR peptides target intracellular regulatory pathways to drive S. meliloti endoreduplication and differentiation during symbiosis.
authors: Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors: Jon
authors: J
authors: Penterman
authors: Ryan P
authors: RP
authors: Abo
authors: Nicole J
authors: NJ
authors: De Nisco
authors: Markus F F
authors: MF
authors: Arnold
authors: Renato
authors: R
authors: Longhi
authors: Matteo
authors: M
authors: Zanda
authors: Graham C
authors: GC
authors: Walker
mesh_terms: D002453:Cell Cycle / Q000502:physiology*; D018076:DNA, Complementary / Q000235:genetics; D007887:Fabaceae / Q000378:metabolism / Q000382:microbiology*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D046228:Microarray Analysis; D008954:Models, Biological; D016133:Polymerase Chain Reaction; D053204:Root Nodules, Plant / Q000378:metabolism / Q000382:microbiology; D016962:Sinorhizobium meliloti / Q000378:metabolism / Q000502:physiology*; D013559:Symbiosis
chemical_list: D018076:DNA, Complementary; D036341:Intercellular Signaling Peptides and Proteins
keywords: host–microbe interactions; rhizobia-legume