MEKK1 is requried for MPK4 activation and regulates tissue specific and temperature dependent cell death in Arabidopsis

1
The Journal of Biological Chemistry. 2006.
MEKK1 is requried for MPK4 activation and
regulates tissue specific and temperature
dependent cell death in Arabidopsis
20. Nov. 2006 lim ji hyuk
2
Introduction
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Various types of plant innate immunity
Immunological Reviews. 198 249-266. 2004
4
Conservation of signaling pathways mediating the
activation of innate immunity in insects,
mammals, and plants.
Immunological Reviews. 198 249-266. 2004
5
Model for the evolution of bacterial resistance
in plants
Cell. 124. 803-814.2006
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MAPK cascades and the cellular responses they
influence following the recognition of microbial
pathogens
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Schematic illustration of MAPK pathways
identified in Arabidopsis, tobacco, and tomato
that are involved in defense-related signal
transduction
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Model describing the role of Arabidopsis,
Medicago and tomato MAPK pathways in abiotic
stress responses
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• The recognition of pathogen derived molecules,
  so called PAMPs, triggers innate immunity
  responses in both animals and plants.
• In plants PAMPs are also recognized by
  LRR-containing receptor kinases.
• Plants recognize such effectors, directly or
  indirectly by resistance (R) proteins and trigger
  rapid defense responses including localized cell
  death.
• The signal transduction following pathogen
  recognition by R proteins and receptor kinases in
  plants are thought to be mediated by MAPK
  cascades as a number of MAPK components are known
  to be activated in these processes.

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Results
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Figure 1.
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Figure 2.
MEKK1 is dispensable for MPK3 and MPK6 activation
by flg22.
Loss of MPK4 activity in mekk1 in response to
flg22 is not due to reduced MPK4 protein levels.
MEKK1 is required for activation of MPK4
triggered by flg22.
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Figure 3.
Figure 4.
H2O2 accumulation is associated with cell death
in the vasculature but not in the guard cells.
MEKK1 negatively regulates tissue-specific cell
death.
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Figure 5.
MEKK1 function leads to constitutive activation
of the defense associated responses.
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Figure 6.
Cotyledon
True leaf
Transverse section of the first leaf
Guard cell on cotyledon
MEKK1 expression is tissue specific and
correlates well with the cell death phenotype and
H2O2 accumulation in leaves.
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Figure 7.
Temperature dependent process is upstream of cell
death and H2O2 accumulation.
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Figure 8.
Tryphan blue
DAB
Aniline blue
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Discussion

• MEKK1 is dispensable for flg22-triggered
  activation of positive regulators of basal
  defense, MPK3 and MPK6.
• MEKK1 is essential for flg22-triggered
  activation of MPK4.
• Defense gene induction is controlled by a finely
  tuned balance of positive and negative regulators
  at the early time point.
• MEKK1 may play an important role in positive and
  negative regulation of parallel MAPK cascades.
• MEKK1 is highly expressed in the vasculature and
  acts as a novel negative regulator in preventing
  cell death and H2O2 accumulation.