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Response of endophytic bacterial communities in potato plants to infection with Erwinia carotovora subsp. atroseptica.

ABSTRACT: The term endophyte refers to interior colonization of plants by microorganisms that do not have pathogenic effects on their hosts, and various endophytes have been found to play important roles in plant vitality. In this study, cultivation-independent terminal restriction fragment length polymorphism analysis of 16S ribosomal DNA directly amplified from plant tissue DNA was used in combination with molecular characterization of isolates to examine the influence of plant stress, achieved by infection with the blackleg pathogen Erwinia carotovora subsp. atroseptica, on the endophytic population in two different potato varieties. Community analysis clearly demonstrated increased bacterial diversity in infected plants compared to that in control plants. The results also indicated that the pathogen stress had a greater impact on the bacteria population than the plant genotype had. Partial sequencing of the 16S rRNA genes of isolated endophytes revealed a broad phylogenetic spectrum of bacteria, including members of the alpha, beta, and gamma subgroups of the Proteobacteria, high- and low-G+C-content gram-positive organisms, and microbes belonging to the Flexibacter-Cytophaga-Bacteroides group. Screening of the isolates for antagonistic activity against E. carotovora subsp. atroseptica revealed that 38% of the endophytes protected tissue culture plants from blackleg disease.

SUBMITTER: Reiter B

PROVIDER: S-EPMC127529 | biostudies-literature | 2002 May

REPOSITORIES: biostudies-literature

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Response of endophytic bacterial communities in potato plants to infection with Erwinia carotovora subsp. atroseptica.

Reiter Birgit B Pfeifer Ulrike U Schwab Helmut H Sessitsch Angela A

Applied and environmental microbiology 20020501 5

The term endophyte refers to interior colonization of plants by microorganisms that do not have pathogenic effects on their hosts, and various endophytes have been found to play important roles in plant vitality. In this study, cultivation-independent terminal restriction fragment length polymorphism analysis of 16S ribosomal DNA directly amplified from plant tissue DNA was used in combination with molecular characterization of isolates to examine the influence of plant stress, achieved by infec ...[more]

PMID: 11976096

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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

Response of endophytic bacterial communities in potato plants to infection with Erwinia carotovora subsp. atroseptica.

Publications

Response of endophytic bacterial communities in potato plants to infection with Erwinia carotovora subsp. atroseptica.

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