Resumen de Signaling in PAMP-triggered immunity in Arabidopsis thaliana
Gerit Bethke, Lennart Eschen Lippold, Justin Lee, Luis Maldonado, Kai Naumann, Pascal Pecher, Stefanie Ranf, Dierk Scheel
Plants detect potential pathogens in their environment via pathogen-associated molecularpatterns (PAMPs) that are recognized by plant plasma membrane receptors. Typical PAMPsinclude the bacterial flagellin-derived flg22 peptide, the elf18 peptide of the bacterial elongationfactor EF-Tu, bacterial peptidoglycans and lipopolysaccharides, as well as fungal chitinoligomers and glucan fragments from oomycetes. PAMP-binding to their receptors initiatescomplex signaling networks that activate a multi-component defense response and therebyestablish PAMP-triggered immunity.One of the earliest detectable responses after PAMP perception is the activation of ion channelsand pumps at the plasma membrane. The resulting ion fluxes, which lead to a transient increasein cytosolic calcium, have been shown to be required for all other downstream responses, suchas the activation of mitogen-activated protein kinases (MAPKs), production of reactive oxygenspecies and defence gene expression. Using a transgenic Arabidopsis line with the calciumreporter, aequorin, rapid increases in cytosolic calcium levels are detected after PAMPapplication. To identify regulators of calcium homeostasis, seeds of aequorin-expressing lineswere mutagenized and the population screened for mutants with changed calcium elevation(cce) in response to flg22 treatment. Many mutants in the flg22 receptor, in receptor complexcomponents and in unknown signaling elements were isolated.MAPK cascades are essential not only for controling the defense response but also manydevelopmental processes. The elements that prevent erroneous signaling crosstalk may includeexpression patterns of the MAPK components, the presence of pathway-specific proteincomplexes or the MAPK substrate diversity. Different strategies have been employed to isolateMAPK substrates and interacting proteins. Results of the functional analysis of severalinteracting proteins in the MAPK signal transduction pathway(s) will be presented.
