title: Analysis of differences between Sinorhizobium meliloti 1021 and 2011 strains using the host calcium spiking response.
abstract: In the Rhizobium-legume symbiosis, compatible partners recognize each other through an exchange of signals. Plant inducers act together with bacterial transcriptional activators, the NodD proteins, to regulate the expression of bacterial biosynthetic nodulation (nod) genes. These genes direct the synthesis of a lipochito-oligosaccharide signal called Nod factor (NF). NFs elicit an early host response, root hair calcium spiking, that is initiated in root hair cells within 15 min of NF or live Rhizobium inoculation. We used calcium spiking as an assay to compare two closely related strains of Sinorhizobium meliloti, Rm1021 and Rm2011, derived from the same field isolate. We found that the two strains show a kinetic difference in the calcium spiking assay: Rm1021 elicits calcium spiking in host root hairs as rapidly as purified NF, whereas Rm2011 shows a significant delay. This difference can be overcome by raising expression levels of either the NodD transcriptional activators or GroEL, a molecular chaperone that affects expression of the biosynthetic nod genes. We further demonstrate that the delay in triggering calcium spiking exhibited by Rm2011 is correlated with a reduced amount of nod gene expression compared with Rm1021. Therefore, calcium spiking is a useful tool in detecting subtle differences in bacterial gene expression that affect the early stages of the Rhizobium-legume symbiosis.
authors.affiliation: Department of Biological Sciences, Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305-5020, USA.
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Wais
authors.forename: Derek H
authors.initials: DH
authors.lastname: Wells
authors.forename: Sharon R
authors.initials: SR
authors.lastname: Long
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D018834:Chaperonin 60 / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D007887:Fabaceae / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D016962:Sinorhizobium meliloti / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D013045:Species Specificity; D013559:Symbiosis / Q000187:drug effects* / Q000235:genetics; D015534:Trans-Activators; D014157:Transcription Factors; D015533:Transcriptional Activation
chemical_list: D001426:Bacterial Proteins; D018834:Chaperonin 60; D004268:DNA-Binding Proteins; D008565:Membrane Proteins; C061268:NodD3 protein, Sinorhizobium meliloti; D010940:Plant Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C045625:nodulin; C072143:NolR protein, Sinorhizobium meliloti; D002118:Calcium