Biology Reference
In-Depth Information
Chapter 7
Mitogen-Activated Protein Kinase Cascades
in Plant Innate Immunity
Abstract Mitogen-activated protein kinase cascades are major signal transduction
systems functioning downstream of pattern recognition receptors upon perception
of PAMP elicitor signals. The MAPKs transduce extracellular stimuli into intracel-
lular transcription factors through activation of Ca 2+ , ROS, SA, JA, and ethylene-
dependent signaling systems, and enhance expression of defense-related genes in
plant innate immune system. A typical MAPK signaling module consists of three
kinases: a MAP kinase kinase kinase (MAPKKK), a MAP kinase kinase (MAPKK),
and a MAP kinase (MAPK). MAPKs function at the bottom of the three-kinase
cascade and are activated by MAPKKs through phosphorylation. The activity of
MAPKKs is, in turn, regulated by MAPKKKs via phosphorylation. MAPKKKs
receive PAMP signals from upstream receptors/sensors to activate the MAPK
signaling system. Several distinct MAPK pathways are involved in activating the
plant immune system. Rather than linear pathways, multiple interconnected MAPK
pathways may be required to transmit elicitor signals and integrate defense
responses. Some MAP kinase cascades are involved in biosynthesis of SA, JA, and
ethylene, which are key plant hormones modulating plant innate immune systems.
MAP kinases play important role in interplay and crosstalk of the plant hormone
signaling systems. Some MAP kinases have been found to be involved in priming
defense responses in systemic acquired resistance. MAP kinases modulate phos-
phorylation of transcription factors to trigger transcription of defense genes. 14-3-3
proteins enhance the activity of MAPKKKs in triggering phosphorylation. MAP
kinases modulate stomatal closure immune responses. Enhanced expression of
some MAP kinases trigger enhanced defense responses against a wide spectrum
of viral, bacterial, fungal, and oomycete pathogens. Potential pathogens secrete
effectors to suppress MAPK signaling system and enhance plant susceptibility.
Keywords MAPK ￿ MAPKK ￿ MAPKKK ￿ Three-kinase cascade ￿ Priming
￿ 14-3-3 proteins ￿ Phosphorylation ￿ Effectors
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