title: PtrA Is Functionally Intertwined with GacS in Regulating the Biocontrol Activity ofPseudomonas chlororaphisPA23.
abstract: In vitroinhibition of the fungal pathogenSclerotinia sclerotiorumbyPseudomonas chlororaphisPA23 is reliant upon a LysR-type transcriptional regulator (LTTR) called PtrA. In the current study, we show that Sclerotinia stem rot and leaf infection are significantly increased in canola plants inoculated with theptrA-mutant compared to the wild type, establishing PtrA as an essential regulator of PA23 biocontrol. LTTRs typically regulate targets that are upstream of and divergently transcribed from the LTTR locus. We identified a short chain dehydrogenase (scd) gene immediately upstream ofptrA. Characterization of ascdmutant revealed that it is phenotypically identical to the wild type. Moreover,scdtranscript abundance was unchanged in theptrAmutant. These findings indicate that PtrA regulation does not involvescd, rather this LTTR controls genes located elsewhere on the chromosome. Employing a combination of complementation and transcriptional analysis we investigated whether connections exist between PtrA and other regulators of biocontrol. BesidesptrA, gacSwas the only gene able to partially rescue the wild-type phenotype, establishing a connection between PtrA and the sensor kinase GacS. Transcriptomic analysis revealed decreased expression of biosynthetic (phzA, prnA) and regulatory genes (phzI, phzR, rpoS, gacA, rsmX, rsmZ, retS) in theptrAmutant; conversely,rsmE, andrsmYwere markedly upregulated. The transcript abundance ofptrAwas nine-fold higher in the mutant background indicating that this LTTR negatively autoregulates itself. In summary, PtrA is an essential regulator of genes required for PA23 biocontrol that is functionally intertwined with GacS.
authors.affiliation: Department of Microbiology, University of Manitoba Winnipeg, MB, Canada.
authors.forename: Nidhi
authors.initials: N
authors.lastname: Shah
authors.affiliation: Department of Microbiology, University of Manitoba Winnipeg, MB, Canada.
authors.forename: Natasha
authors.initials: N
authors.lastname: Klaponski
authors.affiliation: Department of Plant Science, University of Manitoba Winnipeg, MB, Canada.
authors.forename: Carrie
authors.initials: C
authors.lastname: Selin
authors.affiliation: Department of Microbiology, University of Manitoba Winnipeg, MB, Canada.
authors.forename: Rachel
authors.initials: R
authors.lastname: Rudney
authors.affiliation: Department of Plant Science, University of Manitoba Winnipeg, MB, Canada.
authors.forename: W G Dilantha
authors.initials: WG
authors.lastname: Fernando
authors.affiliation: Department of Biological Science, University of Manitoba Winnipeg, MB, Canada.
authors.forename: Mark F
authors.initials: MF
authors.lastname: Belmonte
authors.affiliation: Department of Microbiology, University of Manitoba Winnipeg, MB, Canada.
authors.forename: Teresa R
authors.initials: TR
authors.lastname: de Kievit
keywords: antifungal; autoinducer; degradative enzymes; phenazine; pyrrolnitrin