The alternative sigma factor RpoN is required for hrp activity in Pseudomonas syringae pv. maculicola and acts at the level of hrpL transcription.
beta-Glucuronidase (uidA) reporter gene fusions were constructed for the hrpZ, hrpL, and hrpS genes from the phytopathogen Pseudomonas syringae pv. maculicola strain ES4326. These reporters, as well as an avrRpt2-uidA fusion, were used to measure transcriptional activity in ES4326 and a ES4326 rpoN mutant. rpoN was required for the expression of avrRpt2, hrpZ, and hrpL in vitro in minimal media and in vivo when infiltrated into Arabidopsis thaliana leaves. In contrast, the expression of hrpS was essentially the same in wild-type and rpoN mutant strains. Constitutive expression of hrpL in an rpoN mutant restored hrpZ transcription to wild-type levels, restored the hypersensitive response when infiltrated into tobacco (Nicotiana tobacum), and partially restored the elicitation of virulence-related symptoms but not growth when infiltrated into Arabidopsis leaves. These data indicate that rpoN-mediated control of hrp gene expression acts at the level of hrpL and that in planta growth of P. syringae is not required for the elicitation of disease symptoms.
Hendrickson
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EL
Department of Genetics, Harvard Medical School, Massachusetts General Hospital, Boston 02114, USA.
Guevera
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P
Ausubel
F M
FM
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins; D012321:DNA-Directed RNA Polymerases / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005810:Multigene Family; D009154:Mutation; D010935:Plant Diseases / Q000382:microbiology; D011549:Pseudomonas / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity*; D051877:RNA Polymerase Sigma 54; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014774:Virulence / Q000235:genetics
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C085855:HrpL protein, Pseudomonas syringae; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; D012321:DNA-Directed RNA Polymerases; D051877:RNA Polymerase Sigma 54