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Journal of Bacteriology, March 2001, p. 1870-1880, Vol. 183, No. 6
Department of Plant Microbiology and
Pathology, Plant Sciences Unit, University of Missouri, Columbia,
Missouri 65211
Received 21 August 2000/Accepted 12 December 2000
rsmBEcc specifies a nontranslatable RNA
regulator that controls exoprotein production and pathogenicity in soft
rot-causing Erwinia carotovora subsp.
carotovora. This effect of rsmBEcc
RNA is mediated mostly by neutralizing the function of
RsmAEcc, an RNA-binding protein of E. carotovora subsp. carotovora, which acts as a global
negative regulator. To determine the occurrence of functional homologs
of rsmBEcc in non-soft-rot-causing
Erwinia species, we cloned the rsmB genes of
E. amylovora (rsmBEa) and E. herbicola pv. gypsophilae (rsmBEhg). We
show that rsmBEa in E. amylovora
positively regulates extracellular polysaccharide (EPS) production,
motility, and pathogenicity. In E. herbicola pv.
gypsophilae, rsmBEhg elevates the levels of
transcripts of a cytokinin (etz) gene and stimulates the
production of EPS and yellow pigment as well as motility.
RsmAEa and RsmAEhg have more than 93% identity
to RsmAEcc and, like the latter, function as negative
regulators by affecting the transcript stability of the target gene.
The rsmB genes reverse the negative effects of
RsmAEa, RsmAEhg, and RsmAEcc, but
the extent of reversal is highest with homologous combinations of
rsm genes. These observations and findings that
rsmBEa and rsmBEhg RNA
bind RsmAEcc indicate that the rsmB effect is
channeled via RsmA. Additional support for this conclusion comes from
the observation that the rsmB genes are much more effective as positive regulators in a RsmA+ strain of E. carotovora subsp. carotovora than in its
RsmA
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.6.1870-1880.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Molecular Characterization of Global Regulatory RNA
Species That Control Pathogenicity Factors in Erwinia
amylovora and Erwinia herbicola pv.
gypsophilae
,
derivative. E. herbicola pv. gypsophilae
produces a 290-base rsmB transcript that is not subject to
processing. By contrast, E. amylovora produces 430- and
300-base rsmB transcripts, the latter presumably derived by
processing of the primary transcript as previously noted with the
transcripts of rsmBEcc. Southern blot
hybridizations revealed the presence of rsmB homologs in E. carotovora, E. chrysanthemi, E. amylovora, E. herbicola, E. stewartii and E. rhapontici, as well as in other
enterobacteria such as Escherichia coli, Salmonella
enterica serovar Typhimurium, Serratia marcescens, Shigella
flexneri, Enterobacter aerogenes, Klebsiella pneumoniae, Yersinia
enterocolitica, and Y. pseudotuberculosis. A
comparison of rsmB sequences from several of these
enterobacterial species revealed a highly conserved 34-mer region which
is predicted to play a role in positive regulation by rsmB RNA.
*
Corresponding author. Mailing address: Department of
Plant Microbiology and Pathology, Plant Sciences Unit, University of Missouri, 108 Waters Hall, Columbia, MO 65211. Phone: (573) 882 1892. Fax: (573) 882 0588. E-mail: CHATTERJEEA{at}MISSOURI.EDU.
We affectionately dedicate this paper to the memory of Robert N. Goodman, whose insight and numerous contributions have led to a better
understanding of the biology of these and other plant-pathogenic bacteria.
Journal series 13,022 of the Missouri Agriculture Experiment Station.
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