title: Phenotypic switching in Pseudomonas brassicacearum involves GacS- and GacA-dependent Rsm small RNAs.
abstract: The plant-beneficial bacterium Pseudomonas brassicacearum forms phenotypic variants in vitro as well as in planta during root colonization under natural conditions. Transcriptome analysis of typical phenotypic variants using microarrays containing coding as well as noncoding DNA fragments showed differential expression of several genes relevant to secondary metabolism and of the small RNA (sRNA) genes rsmX, rsmY, and rsmZ. Naturally occurring mutations in the gacS-gacA system accounted for phenotypic switching, which was characterized by downregulation of antifungal secondary metabolites (2,4-diacetylphloroglucinol and cyanide), indoleacetate, exoenzymes (lipase and protease), and three different N-acyl-homoserine lactone molecules. Moreover, in addition to abrogating these biocontrol traits, gacS and gacA mutations resulted in reduced expression of the type VI secretion machinery, alginate biosynthesis, and biofilm formation. In a gacA mutant, the expression of rsmX was completely abolished, unlike that of rsmY and rsmZ. Overexpression of any of the three sRNAs in the gacA mutant overruled the pleiotropic changes and restored the wild-type phenotypes, suggesting functional redundancy of these sRNAs. In conclusion, our data show that phenotypic switching in P. brassicacearum results from mutations in the gacS-gacA system.
authors.affiliation: CEA, DSV, IBEB, SBVME, Laboratoire d’Ecologie Microbienne de la Rhizosphère et d’Environnements Extrèmes (LEMiRE), Saint-Paul-lez-Durance, France.
authors.forename: David
authors.initials: D
authors.lastname: Lalaouna
authors.forename: Sylvain
authors.initials: S
authors.lastname: Fochesato
authors.forename: Lisa
authors.initials: L
authors.lastname: Sanchez
authors.forename: Philippe
authors.initials: P
authors.lastname: Schmitt-Kopplin
authors.forename: Dieter
authors.initials: D
authors.lastname: Haas
authors.forename: Thierry
authors.initials: T
authors.lastname: Heulin
authors.forename: Wafa
authors.initials: W
authors.lastname: Achouak
mesh_terms: D000935:Antifungal Agents / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D053858:Metabolic Networks and Pathways / Q000235:genetics; D046228:Microarray Analysis; D010641:Phenotype; D011549:Pseudomonas / Q000235:genetics / Q000502:physiology*; D012329:RNA, Bacterial / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D000935:Antifungal Agents; D001426:Bacterial Proteins; C091100:GacA protein, Bacteria; D012329:RNA, Bacterial; D034741:RNA, Small Interfering; D014157:Transcription Factors; C074165:lemA protein, bacterial