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Publikationen - Molekulare Signalverarbeitung

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Wasternack, C.; Hause, B. Jasmonsäure – ein universelles Pflanzenhormon: Blütenduft, Abwehr, Entwicklung Biologie in unserer Zeit 44, 164 - 171, (2014) DOI: 10.1002/biuz.201410535

Jasmonsäure (JA) und ihre Metaboliten kommen in allen niederen und höheren Pflanzen vor. Sie sind universell wirksame, aus Lipiden gebildete Signalstoffe bei der Abwehr von biotischem und abiotischem Stress sowie in der pflanzlichen Entwicklung. Rezeptor und Komponenten von JA–Signalketten wurden identifiziert. In der Entwicklung von Blüten, Früchten, Samen, Trichomen oder in der Abwehr von Insekten und Pathogenen treten ähnliche JA-vermittelte Signalproteine auf, die eine Feinregulation der Prozesse erlauben und eine Verbindung (cross-talk) zu anderenPflanzenhormonen aufweisen.

Jayaweera, T.; Siriwardana, C.; Dharmasiri, S.; Quint, M.; Gray, W. M.; Dharmasiri, N. Alternative Splicing of Arabidopsis IBR5 Pre-mRNA Generates Two IBR5 Isoforms with Distinct and Overlapping Functions PLoS ONE 9, e102301, (2014) DOI: 10.1371/journal.pone.0102301

The INDOLE-3-BUTYRIC ACID RESPONSE5 (IBR5) gene encodes a dual specificity phosphatase that regulates plant auxinresponses. IBR5 has been predicted to generate two transcripts through alternative splicing, but alternative splicing of IBR5has not been confirmed experimentally. The previously characterized ibr5-1 null mutant exhibits many auxin related defectssuch as auxin insensitive primary root growth, defective vascular development, short stature and reduced lateral rootdevelopment. However, whether all these defects are caused by the lack of phosphatase activity is not clear. Here wedescribe two new auxin insensitive IBR5 alleles, ibr5-4, a catalytic site mutant, and ibr5-5, a splice site mutant.Characterization of these new mutants indicates that IBR5 is post-transcriptionally regulated to generate two transcripts,AT2G04550.1 and AT2G04550.3, and consequently two IBR5 isoforms, IBR5.1 and IBR5.3. The IBR5.1 isoform exhibitsphosphatase catalytic activity that is required for both proper degradation of Aux/IAA proteins and auxin-induced geneexpression. These two processes are independently regulated by IBR5.1. Comparison of new mutant alleles with ibr5-1indicates that all three mutant alleles share many phenotypes. However, each allele also confers distinct defects implicatingIBR5 isoform specific functions. Some of these functions are independent of IBR5.1 catalytic activity. Additionally, analysis ofthese new mutant alleles suggests that IBR5 may link ABP1 and SCFTIR1/AFBs auxin signaling pathways.

Antolín-Llovera, M.; Ried, M. K.; Parniske, M. Cleavage of the SYMBIOSIS RECEPTOR-LIKE KINASE Ectodomain Promotes Complex Formation with Nod Factor Receptor 5 Curr Biol 24, 422-427, (2014) DOI: 10.1016/j.cub.2013.12.053

Plants form root symbioses with fungi and bacteria to improve their nutrient supply. SYMBIOSIS RECEPTOR-LIKE KINASE (SYMRK) is required for phosphate-acquiring arbuscular mycorrhiza, as well as for the nitrogen-fixing root nodule symbiosis of legumes [1] and actinorhizal plants [2, 3], but its precise function was completely unclear. Here we show that the extracytoplasmic region of SYMRK, which comprises three leucine-rich repeats (LRRs) and a malectin-like domain (MLD) related to a carbohydrate-binding protein from Xenopus laevis [4], is cleaved to release the MLD in the absence of symbiotic stimulation. A conserved sequence motif—GDPC—that connects the MLD to the LRRs is required for MLD release. We discovered that Nod factor receptor 5 (NFR5) [5, 6, 7, 8] forms a complex with the SYMRK version that remains after MLD release (SYMRK-ΔMLD). SYMRK-ΔMLD outcompeted full-length SYMRK for NFR5 interaction, indicating that the MLD negatively interferes with complex formation. SYMRK-ΔMLD is present at lower amounts than MLD, suggesting rapid degradation after MLD release. A deletion of the entire extracytoplasmic region increased protein abundance, suggesting that the LRR region promotes degradation. Curiously, this deletion led to excessive infection thread formation, highlighting the importance of fine-tuned regulation of SYMRK by its ectodomain.
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