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Publikation

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.
Publikation

Schliemann, W.; Strack, D.; Intramolecular stabilization of acylated betacyanins Phytochemistry 49, 585-588, (1998) DOI: 10.1016/S0031-9422(98)00047-8

Racemization and stability of the betacyanins, betanin (betanidin 5-O-glucoside) and amaranthin(betanidin 5-O-glucuronosylglucoside), under acidic conditions were compared with those of the corresponding feruloyl derivatives, lampranthin II and celosianin II. Both acylbetacyanins showed a reduced racemizationvelocity and celosianin II in addition an enhanced stability, possibly caused by intramolecular associationbetween the betanidin and the feruloyl moieties.
Publikation

Schliemann, W.; Steiner, U.; Strack, D.; Betanidin formation from dihydroxyphenylalanine in a model assay system Phytochemistry 49, 1593-1598, (1998) DOI: 10.1016/S0031-9422(98)00276-3

Formation of betanidin, the aglycone of the red–violet betacyanins, has been demonstrated by a two-step model assay system. In the first step, dihydroxyphenylalanine (Dopa) was incubated with a Dopa dioxygenase preparation from Amanita muscaria, resulting in the formation of 4,5-seco-Dopa that spontaneously recyclized to betalamic acid. In the second step, a tyrosinase preparation from Portulaca grandiflora was added to the Dopa dioxygenase assay, resulting in Dopa oxidation followed by a spontaneous formation of cyclo-Dopa that, in turn, reacted spontaneously with betalamic acid to form betanidin. Thus, two enzymatic reactions, Dopa extradiol ring cleavage by the fungal enzyme and Dopa oxidation by the plant enzyme, initiate three spontaneous steps: the formation of cyclo-Dopa and betalamic acid and finally the condensation of these compounds to betanidin.
Publikation

Maier, W.; Schneider, B.; Strack, D.; Biosynthesis of sesquiterpenoid cyclohexenone derivatives in mycorrhizal barley roots proceeds via the glyceraldehyde 3-phosphate/pyruvate pathway Tetrahedron Lett. 39, 521-524, (1998) DOI: 10.1016/S0040-4039(97)10673-6

Incorporation of [1-13C]- and [U-13C6]glucose indicates that the biosynthesis of sesquiterpenoid cyclohexenone derivatives in mycorrhizal barley roots proceeds via the glyceraldehyde 3-phosphate/pyruvate non-mevalonate pathway.Incorporation of label from [1-13C]glucose (•) and [U-13C6]glucose ( − ) into the aglycon part (blumenol C) of blumenin indicates that in barley roots the arbuscular mycorrhizal fungus Glomus intraradices induces the glyceraldehyde 3-phosphate/pyruvate non-mevalonate pathway leading to sesquiterpenoid cyclohexenone derivatives.
Publikation

Eckermann, S.; Schröder, G.; Schmidt, J.; Strack, D.; Edrada, R. A.; Helariutta, Y.; Elomaa, P.; Kotilainen, M.; Kilpeläinen, I.; Proksch, P.; Teeri, T. H.; Schröder, J.; New pathway to polyketides in plants Nature 396, 387-390, (1998) DOI: 10.1038/24652

The repertoire of secondary metabolism (involving the production of compounds not essential for growth) in the plant kingdom is enormous, but the genetic and functional basis for this diversity is hard to analyse as many of the biosynthetic enzymes are unknown. We have now identified a key enzyme in the ornamental plant Gerbera hybrida (Asteraceae) that participates in the biosynthesis of compounds that contribute to insect and pathogen resistance. Plants transformed with an antisense construct of gchs2, a complementary DNA encoding a previously unknown function1,2, completely lack the pyrone derivatives gerberin and parasorboside. The recombinant plant protein catalyses the principal reaction in the biosynthesis of these derivatives: GCHS2 is a polyketide synthase that uses acetyl-CoA and two condensation reactions with malonyl-CoA to form the pyrone backbone of thenatural products. The enzyme also accepts benzoyl-CoA to synthesize the backbone of substances that have become of interest as inhibitors of the HIV-1 protease3,4,5. GCHS2 is related to chalcone synthase (CHS) and its properties define a new class of function in the protein superfamily. It appears that CHS-related enzymes are involved in the biosynthesis of a much larger range of plant products than was previously realized.
Publikation

Schröder, J.; Raiber, S.; Berger, T.; Schmidt, A.; Schmidt, J.; Soares-Sello, A. M.; Bardshiri, E.; Strack, D.; Simpson, T. J.; Veit, M.; Schröder, G.; Plant Polyketide Synthases: A Chalcone Synthase-Type Enzyme Which Performs a Condensation Reaction with Methylmalonyl-CoA in the Biosynthesis of C-Methylated Chalcones Biochemistry 37, 8417-8425, (1998) DOI: 10.1021/bi980204g

Heterologous screening of a cDNA library from Pinus strobus seedlings identified clones for two chalcone synthase (CHS) related proteins (PStrCHS1 and PStrCHS2, 87.6% identity). Heterologous expression in Escherichia coli showed that PStrCHS1 performed the typical CHS reaction, that it used starter CoA-esters from the phenylpropanoid pathway, and that it performed three condensation reactions with malonyl-CoA, followed by the ring closure to the chalcone. PstrCHS2 was completely inactive with these starters and also with linear CoA-esters. Activity was detected only with a diketide derivative (N-acetylcysteamine thioester of 3-oxo-5-phenylpent-4-enoic acid) that corresponded to the CHS reaction intermediate postulated after the first condensation reaction. PstrCHS2 performed only one condensation, with 6-styryl-4-hydroxy-2-pyrone derivatives as release products. The enzyme preferred methylmalonyl-CoA against malonyl-CoA, if only methylmalonyl-CoA was available. These properties and a comparison with the CHS from Pinussylvestris suggested for PstrCHS2 a special function in the biosynthesis of secondary products. In contrast to P. sylvestris, P. strobus contains C-methylated chalcone derivatives, and the methyl group is at the position predicted from a chain extension with methylmalonyl-CoA in the second condensation of the biosynthetic reaction sequence. We propose that PstrCHS2 specifically contributes the condensing reaction with methylmalonyl-CoA to yield a methylated triketide intermediate. We discuss a model that the biosynthesis of C-methylated chalcones represents the simplest example of a modular polyketide synthase.
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