Omanische Heilpflanze im Fokus der Phytochemie IPB-Wissenschaftler und Partner aus Dhofar haben jüngst die omanische Heilpflanze Terminalia dhofarica unter die phytochemische Lupe genommen. Die Pflanze ist reich an…
Geschmack ist vorhersagbar: Mit FlavorMiner. FlavorMiner heißt das Tool, das IPB-Chemiker und Partner aus Kolumbien jüngst entwickelt haben. Das Programm kann, basierend auf maschinellem Lernen (KI), anhand der…
Grunewald, S.; Marillonnet, S.; Hause, G.; Haferkamp, I.; Neuhaus, H. E.; Veß, A.; Hollemann, T.; Vogt, T.;The Tapetal Major Facilitator NPF2.8 is Required for Accumulation of Flavonol Glycosides on the Pollen Surface in Arabidopsis thalianaPlant Cell321727-1748(2020)DOI: 10.1105/tpc.19.00801
The exine of angiosperm pollen grains is usually covered by a complex mix of metabolites including pollen-specific hydroxycinnamic acid amides (HCAAs) and flavonoid glycosides. Whereas the biosynthetic pathways resulting in the formation of HCAAs and flavonol glycosides have been characterized, it is unclear, how these compounds are transported to the pollen surface. In this report we provide several lines of evidence that AtNPF2.8, a member of the nitrate/peptide NTR/PTR family of transporters is required for accumulation and transport of pollen-specific flavonol 3-O-sophorosides, characterized by a glycosidic β-1,2-linkage, to the pollen surface of Arabidopsis. Ectopic, transient expression of this flavonol sophoroside transporter, termed AtFST1, fused to green fluorescent protein (GFP) demonstrated localization of AtFST1 at the plasmalemma in epidermal leaf cells of Nicotiana benthamiana whereas the tapetum-specific AtFST1-expression was confirmed by promAtFST1:GFP-reporter lines. In vitro characterization of AtFST1-activity was achieved by microbial uptake assays based on 14C-labeled flavonol glycosides. Finally, rescue of an fst1-line by complementation with a genomic fragment of the AtFST1 gene restored flavonol glycoside accumulation of pollen grains to wild-type levels corroborating the requirement of AtFST1 for transport of flavonol-3-O-sophorosides from the tapetum to the pollen surface.
Publikation
Tabassum, N.; Eschen-Lippold, L.; Athmer, B.; Baruah, M.; Brode, M.; Maldonado-Bonilla, L. D.; Hoehenwarter, W.; Hause, G.; Scheel, D.; Lee, J.;Phosphorylation‐dependent control of an RNA granule‐localized protein that fine‐tunes defence gene expression at a post‐transcriptional levelPlant J.1011023-1039(2020)DOI: 10.1111/tpj.14573
Mitogen‐activated protein kinase (MAPK) cascades are key signalling modules of plant defence responses to pathogen‐associated molecular patterns (PAMPs, e.g. bacterial flg22 peptide). The Tandem Zinc Finger Protein 9 (TZF9) is an RNA‐binding protein that is phosphorylated by two PAMP‐responsive MAPKs, MPK3 and MPK6. We mapped the major phosphosites in TZF9 and showed their importance for controlling in vitro RNA‐binding activity, in vivo flg22‐induced rapid disappearance of TZF9‐labelled processing body‐like structures and TZF9 protein turnover. Microarray analysis showed a strong discordance between transcriptome (total mRNA) and translatome (polysome‐associated mRNA) in the tzf9 mutant, with more mRNAs associated to ribosomes in the absence of TZF9. This suggests that TZF9 may sequester and inhibit translation of subsets of mRNAs. Fittingly, TZF9 physically interacts with poly(A)‐binding protein 2 (PAB2), a hallmark constituent of stress granules – a site for stress‐induced translational stalling/arrest. TZF9 even promotes stress granule assembly in the absence of stress. Hence, MAPKs may control defence gene expression post‐transcriptionally through release from translation arrest within TZF9‐PAB2‐containing RNA granules or perturbing PAB2 functions in translation control (e.g. in the mRNA closed‐loop model of translation).
Publikation
Rödiger, A.; Galonska, J.; Bergner, E.; Agne, B.; Helm, S.; Alseekh, S.; Fernie, A. R.; Thieme, D.; Hoehenwarter, W.; Hause, G.; Pfannschmidt, T.; Baginsky, S.;Working day and night: plastid casein kinase 2 catalyses phosphorylation of proteins with diverse functions in light‐ and dark‐adapted plastidsPlant J.104546-558(2020)DOI: 10.1111/tpj.14944
Casein kinase 2 is a ubiquitous protein kinase that has puzzled
researchers for several decades because of its pleiotropic activity.
Here, we set out to identify the in vivo targets of plastid casein kinase 2 (pCK2) in Arabidopsis thaliana. Survey phosphoproteome analyses were combined with targeted analyses with wild-type and pck2 knockdown mutants to identify potential pCK2 targets by their decreased phosphorylation state in the mutant. To validate potential substrates, we complemented the pck2 knockdown line with tandem affinity tag (TAP)-tagged pCK2 and found it to restore growth parameters, as well as many, but not all, putative pCK2-dependent phosphorylation events. We further performed a targeted analysis at the end-of-night to increase the specificity of target protein identification. This analysis confirmed light-independent phosphorylation of several pCK2 target proteins. Based on the aforementioned data, we define a set of in vivo
pCK2-targets that span different chloroplast functions, such as
metabolism, transcription, translation and photosynthesis. The
pleiotropy of pCK2 functions is also manifested by altered state
transition kinetics during short-term acclimation and significant
alterations in the mutant metabolism, supporting its function in
photosynthetic regulation. Thus, our data expand our understanding on
chloroplast phosphorylation networks and provide insights into kinase
networks in the regulation of chloroplast functions.
Publikation
Page, J. E.; Hause, G.; Raschke, M.; Gao, W.; Schmidt, J.; Zenk, M. H.; Kutchan, T. M.;Functional Analysis of the Final Steps of the 1-Deoxy-d-xylulose 5-phosphate (DXP) Pathway to Isoprenoids in Plants Using Virus-Induced Gene SilencingPlant Physiol.1341401-1413(2004)DOI: 10.1104/pp.103.038133
Isoprenoid biosynthesis in plant plastids occurs via the 1-deoxy-d-xylulose 5-phosphate (DXP) pathway. We used tobacco rattle virus (TRV) to posttranscriptionally silence the expression of the last two enzymes of this pathway, the IspG-encoded (E)-4-hydroxy-3-methylbut-2-enyl diphosphate synthase (HDS) and the IspH-encoded isopentenyl/dimethylallyl diphosphate synthase (IDDS), as well as isopentenyl/dimethylallyl diphosphate isomerase (IDI), the enzyme that interconverts IPP and DMAPP. TRV-IspG and TRV-IspH infected Nicotiana benthamiana plants had albino leaves that contained less than 4% of the chlorophyll and carotenoid pigments of control leaves. We applied [13C]DXP and [14C]DXP to silenced leaves and found that 2-C-methyl-d-erythritol 2,4-cyclodiphosphate accumulated in plants blocked at HDS while DXP, (E)-4-hydroxy-3-methylbut-2-enyl phosphate and (E)-2-methylbut-2-ene-1,4-diol accumulated in IDDS-blocked plants. Albino leaves from IspG- and IspH-silenced plants displayed a disorganized palisade mesophyll, reduced cuticle, fewer plastids, and disrupted thylakoid membranes. These findings demonstrate the participation of HDS and IDDS in the DXP pathway in plants, and support the view that plastid isoprenoid biosynthesis is metabolically and physically segregated from the mevalonate pathway. IDI-silenced plants had mottled white-pale green leaves with disrupted tissue and plastid structure, and showed an 80% reduction in pigments compared to controls. IPP pyrophosphatase activity was higher in chloroplasts isolated from IDI-silenced plants than in control plant chloroplasts. We suggest that a low level of isoprenoid biosynthesis via the DXP pathway can occur without IDI but that this enzyme is required for full function of the DXP pathway.