Negative autogenous control of the master type III secretion system regulator HrpL in Pseudomonas syringae
File(s)
Published version
Author(s)
Waite, CJ
Schumacher, J
Jovanovic, M
Bennett, M
Buck, M
Type
Journal Article
Abstract
The type III secretion system (T3SS) is a principal virulence determi-
nant of the model bacterial plant pathogen
Pseudomonas syringae
. T3SS effector
proteins inhibit plant defense signaling pathways in susceptible hosts and elicit
evolved immunity in resistant plants. The extracytoplasmic function sigma factor
HrpL coordinates the expression of most T3SS genes. Transcription of
hrpL
is depen-
dent on sigma-54 and the codependent enhancer binding proteins HrpR and HrpS
for
hrpL
promoter activation.
hrpL
is oriented adjacently to and divergently from the
HrpL-dependent gene
hrpJ
, sharing an intergenic upstream regulatory region. We
show that association of the RNA polymerase (RNAP)-HrpL complex with the
hrpJ
promoter element imposes negative autogenous control on
hrpL
transcription in
P. syringae
pv.
tomato
DC3000. The
hrpL
promoter was upregulated in a Δ
hrpL
mu-
tant and was repressed by plasmid-borne
hrpL
. In a minimal
Escherichia coli
back-
ground, the activity of HrpL was sufficient to achieve repression of reconstituted
hrpL
transcription. This repression was relieved if both the HrpL DNA-binding func-
tion and the
hrp
-box sequence of the
hrpJ
promoter were compromised, implying
dependence upon the
hrpJ
promoter. DNA-bound RNAP-HrpL entirely occluded the
HrpRS and partially occluded the integration host factor (IHF) recognition elements
of the
hrpL
promoter
in vitro
, implicating inhibition of DNA binding by these factors
as a cause of negative autogenous control. A modest increase in the HrpL concen-
tration caused hypersecretion of the HrpA1 pilus protein but intracellular accumula-
tion of later T3SS substrates. We argue that negative feedback on HrpL activity fine-
tunes expression of the T3SS regulon to minimize the elicitation of plant defenses.
nant of the model bacterial plant pathogen
Pseudomonas syringae
. T3SS effector
proteins inhibit plant defense signaling pathways in susceptible hosts and elicit
evolved immunity in resistant plants. The extracytoplasmic function sigma factor
HrpL coordinates the expression of most T3SS genes. Transcription of
hrpL
is depen-
dent on sigma-54 and the codependent enhancer binding proteins HrpR and HrpS
for
hrpL
promoter activation.
hrpL
is oriented adjacently to and divergently from the
HrpL-dependent gene
hrpJ
, sharing an intergenic upstream regulatory region. We
show that association of the RNA polymerase (RNAP)-HrpL complex with the
hrpJ
promoter element imposes negative autogenous control on
hrpL
transcription in
P. syringae
pv.
tomato
DC3000. The
hrpL
promoter was upregulated in a Δ
hrpL
mu-
tant and was repressed by plasmid-borne
hrpL
. In a minimal
Escherichia coli
back-
ground, the activity of HrpL was sufficient to achieve repression of reconstituted
hrpL
transcription. This repression was relieved if both the HrpL DNA-binding func-
tion and the
hrp
-box sequence of the
hrpJ
promoter were compromised, implying
dependence upon the
hrpJ
promoter. DNA-bound RNAP-HrpL entirely occluded the
HrpRS and partially occluded the integration host factor (IHF) recognition elements
of the
hrpL
promoter
in vitro
, implicating inhibition of DNA binding by these factors
as a cause of negative autogenous control. A modest increase in the HrpL concen-
tration caused hypersecretion of the HrpA1 pilus protein but intracellular accumula-
tion of later T3SS substrates. We argue that negative feedback on HrpL activity fine-
tunes expression of the T3SS regulon to minimize the elicitation of plant defenses.
Date Issued
2017-01-24
Date Acceptance
2016-12-22
Citation
mBio, 2017, 8 (1)
ISSN
2150-7511
Publisher
American Society for Microbiology
Journal / Book Title
mBio
Volume
8
Issue
1
Copyright Statement
© 2017 Waite et al. This is an openaccess
article distributed under the terms of
the Creative Commons Attribution 4.0
International license (https://creativecommons.org/licenses/by/4.0/)
article distributed under the terms of
the Creative Commons Attribution 4.0
International license (https://creativecommons.org/licenses/by/4.0/)
Subjects
Science & Technology
Life Sciences & Biomedicine
Microbiology
PLANT-PATHOGENIC BACTERIA
PV. TOMATO DC3000
ESCHERICHIA-COLI
GENE-EXPRESSION
PROTEIN SECRETION
RNA-POLYMERASE
PROMOTER
PILUS
VIRULENCE
EVOLUTION
0605 Microbiology
Publication Status
Published
Article Number
e02273-16