Cloning and molecular analysis of structural genes involved in flavonoid and stilbene biosynthesis in grape (Vitis vinifera L.)

Expression of the grape dihydroflavonol reductase gene and analysis of its promoter region

Dihydroflavonol reductase (DFR) is a key enzyme involved in anthocyanin biosynthesis and proanthocyanidin synthesis in grape. DFR catalyses the reduction of dihydroflavonols to leucoanthocyanidins in the anthocyanin pathway. The DFR products, the leucoanthocyanidins, are substrates for the next step in the anthocyanin pathway and are also the substrates for the proanthocyanidin pathway. In the present study the promoter of the grape dfr gene was cloned. Analysis of the dfr promoter sequence revealed the existence of several putative DNA binding motifs. The dfr promoter was fused to the uidA gene and the control of this fusion and the endogenous dfr gene expression, was studied in transformed plants and in red cell suspension originated from fruits. The dfr promoter-uidA gene fusion was expressed in leaves, roots and stems. Deletions of the dfr promoter influenced the specificity of the expression of the GUS gene fusion in plantlet roots and the level of expression in plants and in the red cell suspension originated from fruits. The deletion analysis of the dfr promoter suggests that a specific sequence located between -725 to -233 might be involved in expression of the dfr gene in fruits. Light, calcium and sucrose induced the dfr gene expression. In the transformed suspension cultures, expression of both the endogenous dfr gene and the dfr promoter-uidA gene fusions was induced by white light. The induction by both light and calcium suggests the possible involvement of a UV receptors signal transduction pathway in the induction of the dfr gene. The induction of the dfr gene and the dfr promoter-uidA gene fusions by light and sucrose indicates a close interaction between sucrose and light signalling pathways.

Phytoalexins from the Vitaceae: biosynthesis, phytoalexin gene expression in transgenic plants, antifungal activity, and metabolism

Resistance of plants to infection by phytopathogenic microorganisms is the result of multiple defense reactions comprising both constitutive and inducible barriers. In grapevine, the most frequently observed and best characterized defense mechanisms are the accumulation of phytoalexins and the synthesis of PR-proteins. Particular attention has been given here to stilbene phytoalexins produced by Vitaceae, specifically, their pathway of biosynthesis (including stilbene phytoalexin gene transfer experiments to other plants) and their biological activity together with fungal metabolism.

Reaction mechanism from leucoanthocyanidin to anthocyanidin 3-glucoside, a key reaction for coloring in anthocyanin biosynthesis

In the conversion from colorless leucoanthocyanidin to colored anthocyanidin 3-glucoside, at least two enzymes, anthocyanidin synthase (ANS) and UDP-glucose:flavonoid 3-O-glucosyltransferase (3-GT), are postulated to be involved. Despite the importance of this reaction sequence for coloring in anthocyanin biosynthesis, the biochemical reaction mechanism has not been clarified, and the possible involvement of a dehydratase has not been excluded. Here we show that recombinant ANSs from several model plant species, snapdragon, petunia, torenia, and maize, catalyze the formation of anthocyanidin in vitro through a 2-oxoglutarate-dependent oxidation of leucoanthocyanidin. Crude extracts of Escherichia coli, expressing recombinant ANSs from these plant species, and purified recombinant enzymes of petunia and maize catalyzed the formation of anthocyanidin in the presence of ferrous ion, 2-oxoglutarate, and ascorbate. The in vitro formation of colored cyanidin 3-glucoside from leucocyanidin, via a cyanidin intermediate, was demonstrated using petunia ANS and 3-GT. The entire reaction sequence did not require any additional dehydratase but was dependent on moderate acidic pH conditions following the enzymatic steps. The present study indicated that the in vivo cytosolic reaction sequence involves an ANS-catalyzed 2-oxoglutarate-dependent conversion of leucoanthocyanidin (flavan-3,4-cis-diol) to 3-flaven-2,3-diol (pseudobase), most probably through 2,3-desaturation and isomerization, followed by glucosylation at the C-3 position by 3-GT.

Novel polyketides synthesized with a higher plant stilbene synthase

The physiological function of the stilbene synthase (STS) from groundnut (Arachis hypogaea) is the formation of resveratrol. The enzyme uses 4-coumaroyl-CoA, performs three condensations with malonyl-CoA, and folds the resulting tetraketide into a new aromatic ring system. We investigated the capacity for building novel and unusual polyketides from alternative substrates. Three types of products were obtained: (a) complete reaction (stilbene-type), (b) three condensations without formation of an aromatic ring (CTAL-type pyrone derailment), and (c) two condensations (BNY-type pyrone derailment). All product types were obtained from 4-fluorocinnamoyl-CoA and analogs in which the coumaroyl moiety was replaced by furan or thiophene. Only type (b) and (c) products were synthesized from other 4-substituted 4-coumaroyl-CoA analogs (-Cl, -Br, -OCH3). Benzoyl-CoA, phenylacetyl-CoA, and medium chain aliphatic CoA esters were poor substrates, and the majority of the products were of type (c). The results show that minor modifications can be used to direct the enzyme reaction to form a variety of different and new products. Manipulation of the biosynthesis of polyketides by synthetic analogs could lead to the development of a chemical library of pharmaceutically interesting novel polyketides.

Regulation of anthocyanin biosynthesis in UV-A-irradiated cell cultures of carrot and in organs of intact carrot plants

Two cell lines of Daucus carota are known to differ with respect to anthocyanin accumulation. cDNA clones encoding enzymes involved in anthocyanidin biosynthesis, namely phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), chalcone synthase (CHS; EC 2.3.1.74), flavanone 3-hydroxylase (F3H; EC 1.14.11.9), dihydroflavonol 4-reductase (DFR; EC 1.1.1.219) and leucoanthocyanidin dioxygenase (LDOX; EC 1.14.11.-), were isolated from libraries derived from cell cultures. Northern blot analysis of anthocyanin-accumulating (DCb) and non-accumulating (DCs) cell cultures of carrot showed that the anthocyanin pathway in these anthocyanin-free DCs cells is blocked. The expression of CHS1, DFR1 and LDOX is not detectable. However, F3H and DFR2 behave differently. In the European wild carrot (Daucus carota ssp. carota) the structural genes coding for the enzymes responsible for anthocyanin biosynthesis are strongly expressed in organs which accumulate anthocyanins. Only the dark-purple coloured petals of the central flowers of the inflorescence and to a certain extent the white flowers and the leaves but not the stems and the roots transcribe these genes. To study the effect of anthocyanins as UV-screens the expression of a protein indispensable for cell proliferation like alpha-tubulin (TUB) was monitored.

Two differentially regulated Arabidopsis genes define a new branch of the DFR superfamily

Two tandem genes were identified on Arabidopsis chromosome II (AtCRL1 and AtCRL2) encoding proteins with homology to members of the dihydroflavonol-4-reductase (DFR) superfamily. The encoded CRL1 and CRL2 proteins share 87% mutual amino acid sequence identity whereas their promoter regions are highly divergent, suggesting differential regulation of the CRL genes. Phylogenetic analysis placed CRL1 and CRL2 in a separate branch of the DFR superfamily. Northern blotting showed strong AtCRL1 induction by abscisic acid (ABA), drought, and heat shock, and high expression level in seeds, thus resembling the expression pattern of late embryogenic abundant ABA-responsive genes. Differential expression of the two genes during plant development was confirmed in plants expressing transcriptional fusions between the two promoters and the Escherichia coli beta-glucuronidase reporter gene. This showed that, whereas high expression of AtCRL1 in mature seeds declines during subsequent vegetative growth, transcriptional activity from the AtCRL2 promoter increases during vegetative growth. Expression of both genes is restricted to vascular tissue. Based upon their homology to proteins involved in lignin synthesis, we propose that AtCRL2 is involved in generating conducting tissue late in development, while AtCRL1 is involved in vascular tissue differentiation and/or synthesis in the germinating embryos.

Comparison of UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) gene sequences between white grapes (Vitis vinifera) and their sports with red skin

The expression of the UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) gene has been shown to be critical for anthocyanin biosynthesis in the grape berry. Using white cultivars and bud sports with red skin, we examined the expression of seven anthocyanin biosynthetic genes including the UFGT gene and compared the coding/promoter sequences of the UFGT gene. Northern blot analysis showed that the seven anthocyanin biosynthetic genes were expressed coordinately at higher levels in the red-skin sports than in the white-skin progenitors of the sports. It was especially notable that UFGT gene expression was detected only in the red-skin sports and Kyoho. However, there were no differences in either coding or promoter sequences between Italia (Vitis vinifera) and its red-skin sport Ruby Okuyama, or between Muscat of Alexandria (V. vinifera) and the red-skin sport Flame Muscat. From these findings, the phenotypic change from white to red in the sports is thought to be the result of a mutation in a regulatory gene controlling the expression of UFGT.

Purification, cloning, and heterologous expression of a catalytically efficient flavonol 3-O-galactosyltransferase expressed in the male gametophyte of Petunia hybrida

Flavonols are plant-specific molecules that are required for pollen germination in maize and petunia. They exist in planta as both the aglycone and glycosyl conjugates. We identified a flavonol 3-O-galactosyltransferase (F3GalTase) that is expressed exclusively in the male gametophyte and controls the formation of a pollen-specific class of glycosylated flavonols. Thus an essential step to understanding flavonol-induced germination is the characterization of F3GalTase. Amino acid sequences of three peptide fragments of F3GalTase purified from petunia pollen were used to isolate a full-length cDNA clone. RNA gel blot analysis and enzyme assays confirmed that F3GalTase expression is restricted to pollen. Heterologous expression of the F3GalTase cDNA in Escherichia coli yielded active recombinant enzyme (rF3GalTase) which had the identical substrate specificity as the native enzyme. Unlike the relatively nonspecific substrate usage of flavonoid glycosyltransferases from sporophytic tissues, F3GalTase uses only UDP-galactose and flavonols to catalyze the formation of flavonol 3-O-galactosides. Kinetic analysis showed that the k(cat)/K(m) values of rF3GalTase, using kaempferol and quercetin as substrates, approaches that of a catalytically perfect enzyme. rF3GalTase catalyzes the reverse reaction, generation of flavonols from UDP and flavonol 3-O-galactosides, almost as efficiently as the forward reaction. The biochemical characteristics of F3GalTase are discussed in the context of a role in flavonol-induced pollen germination.

Quantitative motion analysis of subchromosomal foci in living cells using four-dimensional microscopy

The motion of subchromosomal foci and of whole chromosome territories in live human cell nuclei was investigated in four-dimensional space-time images. Visualization of subchromosomal foci was achieved by incorporating Cy3-dUTP into the nuclear DNA of two different cell types after microinjection. A subsequent segregation of the labeled cell nuclei led to the presence of only a few labeled chromosome territories on a background of nonlabeled chromatin (Zink et al.,1998. Hum. Genet. 102:241-251). This procedure yielded many distinct signals in a given cell nucleus. Motion analysis in four-dimensional space-time images was performed using single-particle tracking and a statistical approach to the detection of a possible directional motion of foci relative to the center of mass of a chromosome territory. The accuracy of the analysis was tested using simulated data sets that closely mirrored the experimental setup and using microparticles of known size. Application of the analysis tools to experimental data showed that mutual diffusion-like movements between foci located on different chromosomes were more pronounced than inside the territories. In the time range observed, movements of individual foci could best be described by a random diffusion process. The statistical test for joint directed motion of several foci inside chromosome territories revealed that foci occasionally switched from random to directional motion inside the territories.

Three genes whose expression is induced by stress in Saccharomyces cerevisiae

In this work we report the isolation and characterization of three genes induced by different stress conditions in the yeast Saccharomyces cerevisiae. These genes, named GRE1, GRE2 and GRE3, were identified by the differential display technique using total RNAs obtained from yeast grown under hyperosmotic conditions. Northern analysis of RNA obtained from different growth conditions shows that their corresponding transcripts accumulate not only in response to osmotic stress but also to ionic, oxidative and heat stress. Analysis of the deduced amino acid sequences indicated that GRE1, GRE2 and GRE3 correspond to ORFs YPL223C, YOL151W and YHR104W, respectively. Additionally, it suggested that GRE1 encodes a hydrophilic polypeptide that it is not homologous to any known protein but has features resembling the late embryogenesis abundant (LEA) proteins characterized in higher plants; GRE2 encodes a putative reductase with similarity to plant dihydroflavonol-4-reductases; and GRE3 codifies for a keto-aldose reductase highly related to fungal xylose-reductases. The three genes are induced in the late growth phases in agreement with the presence of PDS elements in their promoter regions. The three of them are under the control of the HOG pathway, even though GRE1 and GRE2 promoter regions do not present the consensus core STRE sequence. In addition, GRE1 and GRE3 are regulated negatively by the cAMP-PKA transduction pathway and positively by the transcriptional factors Msn2p and Msn4p. Gene disruptions of the GRE genes did not show a phenotype in any of the tested stress conditions.

Compartmentalization of interphase chromosomes observed in simulation and experiment

Human interphase chromosomes were simulated as a flexible fiber with excluded volume interaction, which represents the chromatin fiber of each chromosome. For the higher-order structures, we assumed a folding into 120 kb loops and an arrangement of these loops into rosette-like subcompartments. Chromosomes consist of subcompartments connected by small fragments of chromatin. Number and size of subcompartments correspond with chromosome bands in early prophase. We observed essentially separated chromosome arms in both our model calculations and confocal laser scanning microscopy, and measured the same overlap in simulation and experiment. Overlap, number and size of chromosome 15 subcompartments of our model chromosomes agree with subchromosomal foci composed of either early or late replicating chromatin, which were observed at all stages of the cell cycle and possibly provide a functionally relevant unit of chromosome territory compartmentalization. Computed distances of chromosome specific markers both on Mb and 10-100 Mb scale agree with fluorescent in situ hybridization measurements under different preparation conditions.

Genomic organization of the genes encoding dihydroflavonol 4-reductase for flower pigmentation in the Japanese and common morning glories

Genomic DNA segments (approximately 17kb) containing three DFR genes in the Japanese and common morning glories were sequenced. The three DFR genes in both plants were found to be arranged in a tandem array, and all of them comprised six exons with identical intron positions. Their DFR-B genes carrying longer introns than the DFR-A and DFR-C genes were expressed extensively in the young buds of pigmented flowers, and the transcription starting site for the DFR-B mRNA of the Japanese morning glory was determined. The DFR-B gene of the common morning glory was expressed considerably in stems, moderately in sepals and leaves, whereas the DFR-A and DFR-C genes of the same plant were expressed scarcely but significantly in the young flower buds and stems. Several novel mobile element-like sequences of around 200bp were found in the genomic DFR regions. A phylogenetic tree indicated that each DFR gene in the Japanese morning glory is most closely related to the corresponding DFR gene in the common morning glory, and that the DFR-B gene is the most diversified gene among the three DFR genes. These structural and functional features of the DFR genes and their evolutionary implications are discussed.

A fruit-specific putative dihydroflavonol 4-reductase gene is differentially expressed in strawberry during the ripening process

A cDNA clone encoding a putative dihydroflavonol 4-reductase gene has been isolated from a strawberry (Fragaria x ananassa cv Chandler) DNA subtractive library. Northern analysis showed that the corresponding gene is predominantly expressed in fruit, where it is first detected during elongation (green stages) and then declines and sharply increases when the initial fruit ripening events occur, at the time of initiation of anthocyanin accumulation. The transcript can be induced in unripe green fruit by removing the achenes, and this induction can be partially inhibited by treatment of de-achened fruit with naphthylacetic acid, indicating that the expression of this gene is under hormonal control. We propose that the putative dihydroflavonol 4-reductase gene in strawberry plays a main role in the biosynthesis of anthocyanin during color development at the late stages of fruit ripening; during the first stages the expression of this gene could be related to the accumulation of condensed tannins.

Cloning and characterization of Vitis vinifera UDP-glucose:flavonoid 3-O-glucosyltransferase, a homologue of the enzyme encoded by the maize Bronze-1 locus that may primarily serve to glucosylate anthocyanidins in vivo

We report here the cloning and optimized expression at 16 degrees C and the characterization of a Vitis vinifera UDP-glucose:flavonoid 3-O-glucosyltransferase, an enzyme responsible for a late step in grapevine anthocyanin biosynthesis. The properties of this and other UDP-glucose:flavonoid 3-O-glucosyltransferases, homologues of the product encoded by the maize Bronze-1 locus, are a matter of conjecture. The availability of a purified recombinant enzyme allowed for the unambiguous determination of the characteristics of a flavonoid 3-O-glucosyltransferase. Kinetic analyses showed that kcat for glucosylation of cyanidin, an anthocyanidin substrate, is 48 times higher than for glucosylation of the flavonol quercetin, whereas Km values are similar for both substrates. Activity toward other classes of substrates is absent. Cu2+ ions strongly inhibit the action of this and other glucosyltransferases; however, we suggest that this phenomenon in large part is due to Cu2+-mediated substrate degradation rather than inhibition of the enzyme. Additional lines of complementary biochemical data also indicated that in the case of V. vinifera, the principal, if not only, role of UDP-glucose:flavonoid 3-O-glucosyltransferases is to glucosylate anthocyanidins in red fruit during ripening. Other glucosyltransferases with a much higher relative activity toward quercetin are suggested to glucosylate flavonols in a distinct spatial and temporal pattern. It should be considered whether gene products homologous to Bronze-1 in some cases more accurately should be referred to as UDP-glucose:anthocyanidin 3-O-glucosyltransferases.

Expression of anthocyanin biosynthesis pathway genes in red and white grapes

The expression of seven genes from the anthocyanin biosynthesis pathway was determined in different tissues of Shiraz grapevines. All of the tissues contained proanthocyanidins, but only the berry skin accumulated anthocyanins. In most tissues, all of the flavonoid genes except UDP glucose-flavonoid 3-o-glucosyl transferase (UFGT) were expressed, but UFGT expression was only detected in berry skin. Similar patterns of expression were observed in the skin of other red grapes. In white grapes, UFGT expression was not detected. White grape cultivars appear to lack anthocyanins because they lack UFGT, although they also had decreased expression of other flavonoid pathway genes.

Duplication and functional divergence in the chalcone synthase gene family of Asteraceae: evolution with substrate change and catalytic simplification

Plant-specific polyketide synthase genes constitute a gene superfamily, including universal chalcone synthase [CHS; malonyl-CoA:4-coumaroyl-CoA malonyltransferase (cyclizing) (EC 2.3.1.74)] genes, sporadically distributed stilbene synthase (SS) genes, and atypical, as-yet-uncharacterized CHS-like genes. We have recently isolated from Gerbera hybrida (Asteraceae) an unusual CHS-like gene, GCHS2, which codes for an enzyme with structural and enzymatic properties as well as ontogenetic distribution distinct from both CHS and SS. Here, we show that the GCHS2-like function is encoded in the Gerbera genome by a family of at least three transcriptionally active genes. Conservation within the GCHS2 family was exploited with selective PCR to study the occurrence of GCHS2-like genes in other Asteraceae. Parsimony analysis of the amplified sequences together with CHS-like genes isolated from other taxa of angiosperm subclass Asteridae suggests that GCHS2 has evolved from CHS via a gene duplication event that occurred before the diversification of the Asteraceae. Enzyme activity analysis of proteins produced in vitro indicates that the GCHS2 reaction is a non-SS variant of the CHS reaction, with both different substrate specificity (to benzoyl-CoA) and a truncated catalytic profile. Together with the recent results of Durbin et al. [Durbin, M. L., Learn, G. H., Jr., Huttley, G. A. & Clegg, M. T. (1995) Proc. Natl. Acad. Sci. USA 92, 3338-3342], our study confirms a gene duplication-based model that explains how various related functions have arisen from CHS during plant evolution.

Identification of an immediate-early salicylic acid-inducible tobacco gene and characterization of induction by other compounds

Tobacco genes that are induced in response to salicylic acid (SA) treatment with immediate-early kinetics were identified by differential mRNA display. Detailed analysis of IS10a, one cDNA clone identified by this method, revealed induction within 30 min of treatment, with a peak of expression at 3 h, that decayed rapidly thereafter. Treatment with the protein synthesis inhibitor, cycloheximide (CHX), also caused induction of IS10a mRNA to comparable levels, but the IS10a mRNA continued to accumulate after 3 h of induction. In combination, CHX and SA led to a superinduction of IS10a mRNA levels that was also sustained. Half-maximal induction was evident at ca. 100-150 microM SA. In addition to SA, induction of IS10a occurred to varying degrees upon treatment with acetylsalicylic acid, benzoic acid, 2,4-dichlorophenoxyacetic acid, methyl jasmonate, and hydrogen peroxide, whereas treatment with other compounds had no effect. The proteins encoded by IS10a and a second highly homologous cDNA show sequence similarity to UDP-glucose: flavonoid glucosyltransferases.

DIOXYGENASES: Molecular Structure and Role in Plant Metabolism

▪ Abstract  Dioxygenases are nonheme iron-containing enzymes important in the biosynthesis of plant signaling compounds such as abscisic acid, gibberellins, and ethylene and also of secondary metabolites, notably flavonoids and alkaloids. Plant dioxygenases fall into two classes: lipoxygenases and 2-oxoacid-dependent dioxygenases. The latter catalyze hydroxylation, epoxidation, and desaturation reactions; some enzymes catalyze more than one type of reaction in successive steps in a biosynthetic pathway. This review highlights recent discoveries on both enzyme groups, particularly in relation to gibberellin biosynthesis, in vivo activity of 1-aminocyclopropane-1-carboxylate oxidase, and molecular structure/function relationships. Similarities between the roles of monooxygenases and dioxygenases are also discussed.

The expression pattern of alfalfa flavanone 3-hydroxylase promoter-gus fusion in Nicotiana benthamiana correlates with the presence of flavonoids detected in situ

Flavanone 3-hydroxylase is an enzyme acting in the central part of the flavonoid biosynthesis pathway. It is generally encoded by a single gene and seems to have a key position for the regulation in this pathway. These two features make a single f3h promoter-gus fusion a suitable tool to study both the f3h expression and the regulation of this pathway. We present here the spatial and temporal analysis of the expression of an alfalfa flavanone 3-hydroxylase (f3h) promoter-gus fusion introduced into Nicotiana benthamiana. The Medicago sativa (alfalfa) f3h promoter directed gus expression in flowers, stems, leaves and roots. In flowers, GUS activity was observed in pollen grains, in ovules, in ovary placenta and in the epidermis, medullary parenchyma, trichomes and second cortical cellular layer surrounding the vascular bundles of the peduncle. In stems, GUS activity was detected at the same places as in the peduncle except for the medullary parenchyma. In roots, we found GUS staining in root hairs, epidermis and in the vascular bundles of the elongated zone. Finally, in leaves, the f3h promoter expressed essentially in the stalk cells of the multicellular trichomes. The expression pattern of the f3h-gus fusion was correlated to the presence of flavonoids in situ. These data indicate that this construct can be very useful to study factors controlling the production of flavonoids.

Molecular characterization and expression of alfalfa (Medicago sativa L.) flavanone-3-hydroxylase and dihydroflavonol-4-reductase encoding genes

Flavonoids are plant phenolic compounds involved in leguminous plant-microbe interactions. Genes implied in the central branch (chalcone synthase (CHS), chalcone isomerase (CHI)) or in the isoflavonoid branch of the flavonoid biosynthesis pathway have been characterized in Medicago sativa. No information is available to date, however, on genes whose products are involved in the synthesis of other types of flavonoids. In this paper we present the genomic organization as well as the nucleotide sequence of one flavanone-3-hydroxylase (F3H) encoding gene of M. sativa, containing two introns and exhibiting 82-89% similarity at the amino acid level to other F3H proteins. This is the first report on the genomic organization of a f3h gene so far. We present also the sequence of a partial dihydroflavonol-4-reductase (DFR) M. sativa cDNA clone. Southern blot experiments indicated that f3h and dfr genes are each represented by a single gene within the tetraploid genome of M. sativa. By a combination of Northern blot and RT-PCR analysis, we showed that both f3h and dfr genes are expressed in flowers, nodules and roots, with a pattern distinct from chs expression. Finally, we show that dfr is expressed in M. sativa leaves whereas f3h is not. The role played by these two genes in organs other than flowers remains to be determined.

Chalcone synthase-like genes active during corolla development are differentially expressed and encode enzymes with different catalytic properties in Gerbera hybrida (Asteraceae)

Recent studies on chalcone synthase (CHS) and the related stilbene synthase (STS) suggest that the structure of chs-like genes in plants has evolved into different forms, whose members have both different regulation and capacity to code for different but related enzymatic activities. We have studied the diversity of chs-like genes by analysing the structure, expression patterns and catalytic properties of the corresponding enzymes of three genes that are active during corolla development in Gerbera hybrida. The expression patterns demonstrate that chs-like genes are representatives of three distinct genetic programmes that are active during organ differentiation in gerbera. Gchs1 and gchs3 code for typical CHS enzymes, and their gene expression pattern temporally correlates with flavonol (gchs1, gchs3) and anthocyanin (gchs1) synthesis during corolla development. Gchs2 is different. The expression pattern does not correlate with the pigmentation pattern, the amino acid sequence deviates considerably from the consensus of typical CHSs, and the catalytic properties are different. The data indicate that it represents a new member in the large superfamily of chs and chs-related genes.

Molecular and enzymatic characterization of two stilbene synthases from Eastern white pine (Pinus strobus). A single Arg/His difference determines the activity and the pH dependence of the enzymes

Pinus strobus (Eastern white pine) contains stilbenes biosynthetically derived from cinnamoyl-CoA (pinosylvin) or dihydrocinnamoyl-CoA (dihydropinosylvin). We screened a P. strobus cDNA library with a stilbene synthase (STS) probe from Pinus sylvestris. The eight isolated cDNAs represented two closely related STS genes with five amino acid differences in the proteins. The enzyme properties were investigated after heterologous expression in Escherichia coli. Both proteins preferred cinnamoyl-CoA against dihydrocinnamoyl-CoA and thus represented pinosylvin synthases. Otherwise they revealed large differences. STS1 had only 3-5% of the activity of STS2, its pH optimum was shifted to lower values (pH 6), and it synthesized with cinnamoyl-CoA a second unknown product. Site-directed mutagenesis demonstrated that a single Arg-to-His exchange in STS1 was responsible for all of the differences. The proton acceptor properties of His are discussed as the reason for the properties of STS1.