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RsmC of the soft-rotting bacterium Erwinia carotovora subsp. carotovora negatively controls extracellular enzyme and harpin(Ecc) production and virulence by modulating levels of regulatory RNA (rsmB) and RNA-binding protein (RsmA).

ABSTRACT: Previous studies have shown that the production of extracellular enzymes (pectate lyase [Pel], polygalacturonase [Peh], cellulase [Cel], and protease [Prt]) and harpin(Ecc) (the elicitor of hypersensitive reaction) in Erwinia carotovora subsp. carotovora is regulated by RsmA, an RNA-binding protein, and rsmB, a regulatory RNA (Rsm stands for regulator of secondary metabolites) (Y. Liu et al., Mol. Microbiol. 29:219-234, 1998). We have cloned and characterized a novel regulatory gene, rsmC, that activates RsmA production and represses extracellular enzyme and harpin(Ecc) production, rsmB transcription, and virulence in E. carotovora subsp. carotovora. In an rsmC knockout mutant of E. carotovora subsp. carotovora Ecc71 carrying the chromosomal copy of the wild-type rsmA(+) allele, the basal levels of Pel, Peh, Cel, Prt, and harpin(Ecc) as well as the amounts of rsmB, pel-1, peh-1, celV, and hrpN(Ecc) transcripts are high, whereas the levels of rsmA transcripts and RsmA protein are low. Furthermore, the expression of an rsmA-lacZ gene fusion is lower in the RsmC(-) mutant than in the RsmC(+) parent. Conversely, the expression of an rsmB-lacZ operon fusion is higher in the RsmC(-) mutant than in the RsmC(+) parent. These observations establish that RsmC negatively regulates rsmB transcription but positively affects RsmA production. Indeed, comparative studies with an RsmC(-) mutant, an RsmA(-) mutant, and an RsmA(-) RsmC(-) double mutant have revealed that the negative effects on exoprotein production and virulence are due to the cumulative regulatory effects of RsmC on rsmA and rsmB. Exoprotein production by the RsmC(-) mutant is partially dependent on the quorum sensing signal, N-(3-oxohexanoyl)-L-homoserine lactone. Southern blot data and analysis of PCR products disclosed the presence of rsmC sequences in E. carotovora subsp. atroseptica, E. carotovora subsp. betavasculorum, and E. carotovora subsp. carotovora. These findings collectively support the idea that rsmA and rsmB expression in these plant pathogenic Erwinia species is controlled by RsmC or a functional homolog of RsmC.

SUBMITTER: Cui Y

PROVIDER: S-EPMC103632 | biostudies-literature | 1999 Oct

REPOSITORIES: biostudies-literature

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rsmC of the soft-rotting bacterium Erwinia carotovora subsp. carotovora negatively controls extracellular enzyme and harpin(Ecc) production and virulence by modulating levels of regulatory RNA (rsmB) and RNA-binding protein (RsmA).

Cui Y Y Mukherjee A A Dumenyo C K CK Liu Y Y Chatterjee A K AK

Journal of bacteriology 19991001 19

Previous studies have shown that the production of extracellular enzymes (pectate lyase [Pel], polygalacturonase [Peh], cellulase [Cel], and protease [Prt]) and harpin(Ecc) (the elicitor of hypersensitive reaction) in Erwinia carotovora subsp. carotovora is regulated by RsmA, an RNA-binding protein, and rsmB, a regulatory RNA (Rsm stands for regulator of secondary metabolites) (Y. Liu et al., Mol. Microbiol. 29:219-234, 1998). We have cloned and characterized a novel regulatory gene, rsmC, that ...[more]

PMID: 10498717

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Project description:Erwinia carotovora subsp. carotovora produces extracellular pectate lyase (Pel), polygalacturonase (Peh), cellulase (Cel), and protease (Prt). The concerted actions of these enzymes largely determine the virulence of this plant-pathogenic bacterium. E. carotovora subsp. carotovora also produces HarpinEcc, the elicitor of the hypersensitive reaction. We document here that KdgREcc (Kdg, 2-keto-3-deoxygluconate; KdgR, general repressor of genes involved in pectin and galacturonate catabolism), a homolog of the E. chrysanthemi repressor, KdgREch and the Escherichia coli repressor, KdgREco, negatively controls not only the pectinases, Pel and Peh, but also Cel, Prt, and HarpinEcc production in E. carotovora subsp. carotovora. The levels of pel-1, peh-1, celV, and hrpNEcc transcripts are markedly affected by KdgREcc. The KdgREcc- mutant is more virulent than the KdgREcc+ parent. Thus, our data for the first time establish a global regulatory role for KdgREcc in E. carotovora subsp. carotovora. Another novel observation is the negative effect of KdgREcc on the transcription of rsmB (previously aepH), which specifies an RNA regulator controlling exoenzyme and HarpinEcc production. The levels of rsmB RNA are higher in the KdgREcc- mutant than in the KdgREcc+ parent. Moreover, by DNase I protection assays we determined that purified KdgREcc protected three 25-bp regions within the transcriptional unit of rsmB. Alignment of the protected sequences revealed the 21-mer consensus sequence of the KdgREcc-binding site as 5'-G/AA/TA/TGAAA[N6]TTTCAG/TG/TA-3'. Two such KdgREcc-binding sites occur in rsmB DNA in a close proximity to each other within nucleotides +79 and +139 and the third KdgREcc-binding site within nucleotides +207 and +231. Analysis of lacZ transcriptional fusions shows that the KdgR-binding sites negatively affect the expression of rsmB. KdgREcc also binds the operator DNAs of pel-1 and peh-1 genes and represses expression of a pel1-lacZ and a peh1-lacZ transcriptional fusions. We conclude that KdgREcc affects extracellular enzyme production by two ways: (i) directly, by inhibiting the transcription of exoenzyme genes; and (ii) indirectly, by preventing the production of a global RNA regulator. Our findings support the idea that KdgREcc affects transcription by promoter occlusion, i.e., preventing the initiation of transcription, and by a roadblock mechanism, i.e., by affecting the elongation of transcription.

Dataset Information

RsmC of the soft-rotting bacterium Erwinia carotovora subsp. carotovora negatively controls extracellular enzyme and harpin(Ecc) production and virulence by modulating levels of regulatory RNA (rsmB) and RNA-binding protein (RsmA).

Publications

rsmC of the soft-rotting bacterium Erwinia carotovora subsp. carotovora negatively controls extracellular enzyme and harpin(Ecc) production and virulence by modulating levels of regulatory RNA (rsmB) and RNA-binding protein (RsmA).

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