Publikationen - Molekulare Signalverarbeitung

Recognition of pathogen-associated molecular patterns (PAMPs) induces multiple defense mechanisms to limit pathogen growth. Here, we show that the Arabidopsis thaliana tandem zinc finger protein 9 (TZF9) is phosphorylated by PAMP-responsive mitogen-activated protein kinases (MAPKs) and is required to trigger a full PAMP-triggered immune response. Analysis of a tzf9 mutant revealed attenuation in specific PAMP-triggered reactions such as reactive oxygen species accumulation, MAPK activation and, partially, the expression of several PAMP-responsive genes. In accordance with these weaker PAMP-triggered responses, tzf9 mutant plants exhibit enhanced susceptibility to virulent Pseudomonas syringae pv. tomato DC3000. Visualization of TZF9 localization by fusion to green fluorescent protein revealed cytoplasmic foci that co-localize with marker proteins of processing bodies (P-bodies). This localization pattern is affected by inhibitor treatments that limit mRNA availability (such as cycloheximide or actinomycin D) or block nuclear export (leptomycin B). Coupled with its ability to bind the ribohomopolymers poly(rU) and poly(rG), these results suggest involvement of TZF9 in post-transcriptional regulation, such as mRNA processing or storage pathways, to regulate plant innate immunity.

A strategy to detect and quantify the polar ethylene precursor 1-aminocyclopropan-1-carboxylic acid (ACC) along with the more apolar phytohormones abscisic acid (ABA), indole-3-acetic acid (IAA), jasmonic acid (JA), jasmonic acid-isoleucine conjugate (JA-Ile), 12-oxo-phytodienoic acid (OPDA), trans-zeatin, and trans-zeatin 9-riboside using a single extraction is presented. Solid phase resins commonly employed for extraction of phytohormones do not allow the recovery of ACC. We circumvent this problem by attaching an apolar group to ACC via derivatization with the amino group specific reagent 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl). Derivatization in the methanolic crude extract does not modify other phytohormones. The derivatized ACC could be purified and detected together with the more apolar phytohormones using common solid phase extraction resins and reverse phase HPLC/electrospray negative ion tandem mass spectrometry. The limit of detection was in the low nanomolar range for all phytohormones, a sensitivity sufficient to accurately determine the phytohormone levels from less than 50 mg (fresh weight) of Arabidopsis thaliana and Nicotiana benthamiana tissues. Comparison with previously published phytohormone levels and the reported changes in phytohormone levels after stress treatments confirmed the accuracy of the method.

Developmental expression of a 23 kDa jasmonate-induced protein (JIP-23) of barley leaves (Hordeum vulgare cv. Salome) was studied by measuring the time-dependent accumulation of transcript and protein during germination. Tissue-specific expression of JIP-23 was analyzed immunocytochemically and by in situ hybridizations, respectively. During seed germination JIP-23 mRNA was found to accumulate transiently with a maximum at 32 h, whereas the protein was steadily detectable after the onset of expression. The occurrence of new isoforms of JIP-23 during germination in comparison to jasmonate-treated leaves suggests, that the JIP-23 gene family of barley is able to express different subsets of isoforms dependent on the developmental stage.JIP-23 and its transcript were found mainly in the scutellum, the scutellar nodule and in lower parts of the primary leaf of 6 days old seedlings. All these tissues exhibited high levels of endogenous jasmonates. In situ hybridization revealed specific accumulation of JIP-23 mRNA in companion cells of the phloem in the nodule plate of the scutellum. In accordance with that, JIP-23 was detected immunocytochemically in phloem cells of the root as well as of the scutellar nodule and in parenchymatic cells of the scutellum. The cell type-specific occurrence of JIP-23 was restricted to cells, which are known to be highly stressed osmotically by active solute transport. This observation suggests, that the expression of this protein might be a response to osmotic stress during development.