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Publications - Cell and Metabolic Biology

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Publications

Sheikh, A. H.; Fraz Hussain, R. M.; Tabassum, N.; Badmi, R.; Marillonnet, S.; Scheel, D.; Lee, J.; Sinha, A.; Possible role of WRKY transcription factors in regulating immunity in Oryza sativa ssp. indica Physiol. Mol. Plant Pathol. 114, 101623, (2021) DOI: 10.1016/j.pmpp.2021.101623

Plants have developed a robust transcription machinery to combat potential pathogenic organisms. One of the hallmarks of early immune responses is the activation of the WRKY transcription factors post infection. Specific WRKYs proteins from Arabidopsis are known substrates of MAPK pathway to mediate the flg22 elicited early immunity. In the current study, using the Golden Gate cloning strategy, we aim to clone the entire WRKY transcription factor family from Oryza sativa ssp. indica consisting of more than 100 members and study their MAPK interaction and subsequent role in PTI. Using a reporter LUC assay in protoplasts we investigated the early defense responses in a few interesting OsWRKY candidates. Interestingly, we observed stringent regulation of WRKY expression in cells and their transcriptional expression only under specific stress responses. The phenomenon of gene expression regulation by intron retention (IR) was prevalently observed in rice WRKY transcripts. We could show the role of WRKY8, 24, and 77 in early defense responses. It was observed that WRKY24 enhanced the expression of early defense response marker genes like NHL10 while WRKY8 and WRKY77 supressed their expression. This study highlights the complicated mechanism by which OsWRKYs expression is possibly regulated and the distinctive roles of some individual members in plant immunity. At the same time this study serves as a cautionary warning for plant researchers to be mindful of the intron retention mechanism while cloning OsWRKYs.
Publications

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 level Plant J. 101, 1023-1039, (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).
Publications

Varet, A.; Hause, B.; Hause, G.; Scheel, D.; Lee, J.; The Arabidopsis NHL3 Gene Encodes a Plasma Membrane Protein and Its Overexpression Correlates with Increased Resistance to Pseudomonas syringae pv. tomato DC3000 Plant Physiol. 132, 2023-2033, (2003) DOI: 10.1104/pp.103.020438

The Arabidopsis genome contains a family of NDR1/HIN1-like (NHL) genes that show homology to the nonrace-specific disease resistance (NDR1) and the tobacco (Nicotiana tabacum) harpin-induced (HIN1) genes. NHL3 is a pathogen-responsive member of this NHL gene family that is potentially involved in defense. In independent transgenic NHL3-overexpressing plant lines, a clear correlation between increased resistance to virulent Pseudomonas syringae pv. tomato DC3000 and enhanced NHL3 transcript levels was seen. These transgenic plants did not show enhanced pathogenesis-related gene expression or reactive oxygen species accumulation. Biochemical and localization experiments were performed to assist elucidation of how NHL3 may confer enhanced disease resistance. Gene constructs expressing amino-terminal c-myc-tagged or carboxyl-terminal hemagglutinin epitope (HA)-tagged NHL3 demonstrated membrane localization in transiently transformed tobacco leaves. Stable Arabidopsis transformants containing the NHL3-HA construct corroborated the findings observed in tobacco. The detected immunoreactive proteins were 10 kD larger than the calculated size and could be partially accounted for by the glycosylation state. However, the expected size was not attained with deglycosylation, suggesting possibly additional posttranslational modification. Detergent treatment, but not chemicals used to strip membrane-associated proteins, could displace the immunoreactive signal from microsomal fractions, showing that NHL3 is tightly membrane associated. Furthermore, immunofluorescence and immunogold labeling, coupled with two-phase partitioning techniques, revealed plasma membrane localization of NHL3-HA. This subcellular localization of NHL3 positions it at an initial contact site to pathogens and may be important in facilitating interception of pathogen-derived signals.
Publications

Schmidt, A.; Grimm, R.; Schmidt, J.; Scheel, D.; Strack, D.; Rosahl, S.; Cloning and Expression of a Potato cDNA Encoding Hydroxycinnamoyl-CoA:Tyramine N-(Hydroxycinnamoyl)transferase J. Biol. Chem. 274, 4273-4280, (1999) DOI: 10.1074/jbc.274.7.4273

Hydroxycinnamoyl-CoA:tyramineN-(hydroxycinnamoyl)transferase (THT; EC 2.3.1.110) catalyzes the transfer of hydroxycinnamic acids from the respective CoA esters to tyramine and other amines in the formation ofN-(hydroxycinnamoyl)amines. Expression of THT is induced byPhytophthora infestans, the causative agent of late blight disease in potato. The amino acid sequences of nine endopeptidase LysC-liberated peptides from purified potato THT were determined. Using degenerate primers, a THT-specific fragment was obtained by reverse transcription-polymerase chain reaction, and THT cDNA clones were isolated from a library constructed from RNA of elicitor-treated potato cells. The open reading frame encoding a protein of 248 amino acids was expressed in Escherichia coli. Recombinant THT exhibited a broad substrate specificity, similar to that of native potato THT, accepting cinnamoyl-, 4-coumaroyl-, caffeoyl-, feruloyl- and sinapoyl-CoA as acyl donors and tyramine, octopamine, and noradrenalin as acceptors tested. Elicitor-induced THT transcript accumulation in cultured potato cells peaked 5 h after initiation of treatment, whereas enzyme activity was highest from 5 to 30 h after elicitation. In soil-grown potato plants, THT mRNA was most abundant in roots. Genomic Southern analyses indicate that, in potato, THT is encoded by a multigene family.
Publications

Schmidt, A.; Scheel, D.; Strack, D.; Elicitor-stimulated biosynthesis of hydroxycinnamoyltyramines in cell suspension cultures of Solanum tuberosum Planta 205, 51-55, (1998) DOI: 10.1007/s004250050295

Treatment of suspension-cultured potato cells (Solanum tuberosum L. cv. Desirée) with an elicitor from Phytophthora infestans induced increased incorporation of 4-hydroxybenzaldehyde, 4-hydroxybenzoate, and N-4-coumaroyl- and N-feruloyltyramine into the cell␣wall and secretion of N-4-coumaroyl- and N-feruloyltyramine into the culture medium. Induced metabolite accumulation was preceded by rapid and transient increases in activities of phenylalanine ammonia-lyase (EC 4.3.1.5) and tyrosine decarboxylase (TyrDC; EC 4.1.1.25), exhibiting maximal activities 5–10 h after initiation of elicitor treatment. Activities of hydroxycinnamoyl-CoA:tyramine hydroxycinnamoyltransferase (EC 2.3.1.110), catalyzing the formation of N-4-coumaroyl- and N-feruloyltyramine, increased later and remained at high levels. The phenolic defense compounds appear to be involved in cell wall reinforcement and may further directly affect fungal growth in the apoplastic space.
Publications

Keller, H.; Hohlfeld, H.; Wray, V.; Hahlbrock, K.; Scheel, D.; Strack, D.; Changes in the accumulation of soluble and cell wall-bound phenolics in elicitor-treated cell suspension cultures and fungus-infected leaves of Solanum tuberosum Phytochemistry 42, 389-396, (1996) DOI: 10.1016/0031-9422(95)00866-7

Cell suspension cultures of potato (Solanum tuberosum cv. Datura) treated with an elicitor preparation from Phytophthora infestans and potato leaves infected with the same fungus were used to study changes in the accumulation patterns of soluble and cell wall-bound phenolics. The compounds were identified by chromatographic comparison with authentic substances and by spectroscopic methods (FAB mass spectrometry, 1H and 13C NMR). The soluble phenolics were 4-O-β-glucopyranosylhydroquinone (arbutin), 4-O-β-glucopyranosylbenzoate, 3-methoxy-4-O-β-glucopyranosylbenzoate (vanillate glucoside), N-(E)-caffeoylputrescine, 2-O-β-glucopyranosylbenzoate (salicylate glucoside), N-(E)-feruloylputrescine, and N-(E)-feruloylaspartate. The cell wall-bound phenolics were 4-hydroxybenzoate, 4-hydroxybenzaldehyde, 3-methoxy-4-hydroxybenzaldehyde (vanillin), 4-(E)-coumarate, (E)-ferulate, N-4-(E)-coumaroyltyramine, and N-(E)-feruloyltyramine. The most prominent phenolics showing elicitor- or fungus-induced increases in accumulation rates were the soluble putrescine amides and cell wall-bound 4-hydroxybenzaldehyde and tyramine amides. In addition, there was a secretion of large amounts of coumaroyltyramine into the cell culture medium.
Publications

Hohlfeld, H.; Scheel, D.; Strack, D.; Purification of hydroxycinnamoyl-CoA:tyramine hydroxycinnamoyltransferase from cell-suspension cultures of Solanum tuberosum L. cv. Datura Planta 199, 166-168, (1996) DOI: 10.1007/BF00196893

A pathogen-elicitor-inducible acyltransferase [tyramine hydroxycinnamoyltransferase (THT); EC 2.3.1], which catalyzes the transfer of hydroxycinnamic acids from hydroxycinnamoyl-CoA esters to tyramine in the formation of N-hydroxycinnamoyltyramine, was purified to apparent homogeneity from cell-suspension cultures of potato (Solanum tuberosum L. cv. Datura), with a 1400-fold enrichment, a 5% recovery and a final specific activity of 208 mkat·(kg protein)−1. Affinity chromatography on Reactive Yellow-3-Agarose using the acyl donor (feruloyl-CoA) as eluent was the decisive step in the purification sequence. The purified protein showed a native molecular mass of ca. 49 kDa. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence and in the absence of a reducing agent (2-mercaptoethanol) indicated that THT is a heterodimer in which the protein subunits (ca. 25 kDa) are non-covalently associated. The enzyme was stimulated fivefold by 10 mM Ca2+. The apparent K m value for tyramine was dependent on the nature of the hydroxycinnamoyl-CoA present. Thus, the K m value for tyramine was about tenfold greater (174 μM) in the presence of 4-coumaroyl-CoA than in the presence of feruloyl-CoA (20 μM).
Publications

Hohlfeld, H.; Schurmann, W.; Scheel, D.; Strack, D.; Partial Purification and Characterization of Hydroxycinnamoyl-Coenzyme A:Tyramine Hydroxycinnamoyltransferase from Cell Suspension Cultures of Solanum tuberosum Plant Physiol. 107, 545-552, (1995) DOI: 10.1104/pp.107.2.545

A pathogen elicitor-inducible soluble acyltransferase (tyramine hydroxycinnamoyltransferase [THT], EC 2.3.1), which catalyzes the transfer of hydroxycinnamic acids from hydroxycinnamoyl-coenzyme A (CoA) esters to tyramine in the formation of N-hydroxycinnamoyltyramine, was partially purified with a 380-fold enrichment and a 6% recovery from cell-suspension cultures of potato (Solanum tuberosum L. cv Datura). The enzyme showed specific activities of 33 mkat (kg protein)-1 (formation of feruloyltyramine). The apparent native Mr was found to be approximately 49,000. Highest activity was at pH 6.8 in K-phosphate. The isoelectric point of the enzyme was approximately pH5.2. The apparent energy of activation was calculated to be 96 kJ mol-1. The enzyme activity was stimulated more than 5-fold by 10 mM Ca2+ or Mg2+. The apparent Km values were 36 [mu]M for feruloyl-CoA and 85 and 140 [mu]M for cinnamoyl- and 4-coumaroyl-CoA, respectively. The Km value for tyramine in the presence of feruloyl-CoA was 22 [mu]M. In the presence of 4-coumaroyl-CoA, however, the Km for tyramine increased to about 230 [mu]M. The mode of action was an iso-ordered bi bi mechanism in which A, B, P, and Q equal hydroxycinnamoyl-CoA, tyramine, N-hydroxycinnamoyltyramine, and CoA, respectively. Thus, the reaction occurred in a ternary complex of the enzyme and substrates. The equilibrium constant of the reaction was determined to be 1.3 x 104. This gave a [delta]G[deg][prime] eq value of -23.5 kJ mol-1.
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