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Analysis of CERK1 ectodomain shedding and the role of XLG2 in cerk1-4 cell death execution

dc.contributor.advisorPetutschnig, Elena K Dr.
dc.contributor.authorMeusel, Christopher
dc.titleAnalysis of CERK1 ectodomain shedding and the role of XLG2 in cerk1-4 cell death executionde
dc.contributor.refereeLipka, Volker Prof. Dr.
dc.description.abstractengConserved microbial signatures are perceived via plasma membrane localized pattern recognition receptors (PRRs). In Arabidopsis, perception of the fungal cell wall component chitin requires the LysM receptor-like kinase CERK1. CERK1 is post-translationally modified to release a soluble ectodomain derivative into the apoplast. The ectodomain fragment is likely to be generated by a proteolytic mechanism called ectodomain shedding. Ectodomain shedding is well documented in animals, where it fulfils diverse regulatory functions on a range of different proteins. In plants, ectodomain shedding has so far only been reported for CERK1 and the function of CERK1 ectodomain shedding is unknown. Some evidence for a role in cell death control comes from cerk1-4, a CERK1 mutant that lacks the soluble ectodomain fragment and is characterized by enhanced cell death upon pathogen attack and in senescence. The first part of the present study focused on the analysis of CERK1 ectodomain shedding and its function in the development of the cerk1-4 phenotype. Arabidopsis accessions were found to vary regarding the abundance of the shed CERK1 ectodomain. The presence of prolines within the extracellular stalk of CERK1 positively correlated with ectodomain abundance. CERK1 variants lacking specific proline residues showed reduced ectodomain abundance, but did not suppress the development of the cerk1-4 phenotype. Point mutations targeting possible protease recognition motifs or variations in extracellular stalk length did not abolish CERK1 ectodomain shedding. Similarly, replacement of the CERK1 transmembrane domain and extracellular stalk with corresponding regions from the flagellin receptor FLS2 had little impact on ectodomain shedding. In mass spectrometry analyses of cell culture supernatants and apoplastic wash fluids, peptides corresponding to extracellular domains of numerous RLKs were identified. The peptides probably derived from ectodomain which were proteolytically released into the apoplast. These results indicate that ectodomain shedding might be a common post-translational modification in plants. The second part of this study focused on the identification of signal transduction components which are essential for development of the cerk1-4 phenotype. A novel mutant fully suppressing the cerk1-4 phenotype was isolated from a genetic screen. The underlying mutation was mapped to the extra-large G-protein 2 (XLG2), which has recently been proposed to act as a G-protein α-subunit.  In the suppressor mutant, a highly conserved glutamic acid was substituted by lysine in the N-terminal part of XLG2. Complementation studies showed that XLG2 fusions with an N-terminal fluorescence protein tag are functional, while C-terminal fusions are not. Confocal microscopy of stably transformed Arabidopsis plants expressing Venus-XLG2 revealed localization to the cell periphery. A subpopulation of Venus-XLG2 accumulates in the nucleus upon diverse stimuli such as water and PAMP infiltration, wounding or pathogen attack. XLG2 has recently been shown to physically interact with canonical heterotrimeric G-protein βγ-dimers. Also, G-protein β- and γ-subunits were shown to be required for full development of the cerk1-4 phenotype. Interestingly, in the G-protein β-subunit mutant agb1, a subpopulation of Venus-XLG2 was localized to the nucleus already in untreated cells. These results suggest that XLG2 subcellular localization is modulated by interaction with G-protein βγ-subunits, which in turn affects its action on downstream targets.  de
dc.contributor.coRefereeTeichmann, Thomas PD Dr.
dc.contributor.thirdRefereeFeussner, Ivo Prof. Dr.
dc.contributor.thirdRefereeFulda, Martin Dr.
dc.contributor.thirdRefereeGatz, Christiane Prof. Dr.
dc.contributor.thirdRefereePolle, Andrea Prof. Dr.
dc.subject.engchitin signalingde
dc.affiliation.instituteBiologische Fakultät für Biologie und Psychologiede
dc.subject.gokfullBiologie (PPN619462639)de

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