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PubMed1989

Decreased-activity mutants of phosphoglucose isomerase in the cytosol and chloroplast of Clarkia xantiana. Impact on mass-action ratios and fluxes to sucrose and starch, and estimation of Flux Control Coefficients and Elasticity Coefficients.

1. Subcellular-compartment-specific decreased-activity mutants of phosphoglucose isomerase in Clarkia xantiana were used to analyse the control of sucrose and starch synthesis during photosynthesis. Mutants were available in which the plastid phosphoglucose isomerase complement is decreased to 75% or 50% of the wild-type level, and the cytosol complement to 64%, 36% or 18% of the wild-type level. 2. The effects on the [product]/[substrate] ratio and on fluxes to sucrose or starch and the rate of photosynthesis were studied with the use of saturating or limiting light intensity to impose a high or low flux through these pathways. 3. Removal of a small fraction of either phosphoglucose isomerase leads to a significant shift of the [product]/[substrate] ratio away, from equilibrium. We conclude that there is no 'excess' of enzyme over that needed to maintain its reactants reasonably close to equilibrium. 4. Decreased phosphoglucose isomerase activity can also alter the fluxes to starch or sucrose. However, the effect on flux does not correlate with the extent of disequilibrium, and also varies depending on the subcellular compartment and on the conditions. 5. The results were used to estimate Flux Control Coefficients for the chloroplast and cytosolic phosphoglucose isomerases. The chloroplast isoenzyme exerts control on the rate of starch synthesis and on photosynthesis in saturating light intensity and CO2, but not at low light intensity. The cytosolic enzyme only exerts significant control when its complement is decreased 3-5-fold, and differs from the plastid isoenzyme in exerting more control in low light intensity. It has a positive Control Coefficient for sucrose synthesis, and a negative Control Coefficient for starch synthesis. 6. The Elasticity Coefficients in vivo of the cytosolic phosphoglucose isomerase were estimated to lie between 5 and 8 in the wild-type. They decrease in mutants with a lowered complement of cytosolic phosphoglucose isomerase. 7. The implications of these results for regulation and for evolution are discussed.

Chloroplasts↗
PubMed1998

Acetyl-CoA:benzylalcohol acetyltransferase--an enzyme involved in floral scent production in Clarkia breweri.

Volatile esters impart distinct characteristics to the floral scent of many plants, and are important in attracting insect pollinators. They are also important flavor compounds in fruits. The ester benzylacetate is a major constituent of the floral scent of Clarkia breweri, an annual plant native to California. The enzyme acetyl-CoA:benzylalcohol acetyltransferase (BEAT), which catalyzes the formation of benzylacetate, has been purified from C. breweri petals, and a cDNA encoding this enzyme has been isolated and characterized. The sequence of the 433-residue BEAT protein does not show high similarity to any previously characterized protein, but a 35-residue region from position 135-163 has significant similarity (42-56% identity) to several proteins known or suspected to use an acyl-CoA substrate. E. coli cells expressing C. breweri BEAT produced enzymatically active protein, and also synthesized benzylacetate and secreted it into the medium. Of the different parts of the C. breweri flower, petals contained the majority of BEAT transcripts, and no BEAT mRNA was detected in leaves. The levels of BEAT mRNA in the petals increased as the bud matured, and peaked at anthesis, paralleling changes in BEAT activity. However, three days after anthesis, mRNA levels began a steep decline, whereas BEAT activity remained high for the next two days, suggesting that the BEAT protein is relatively stable.

Acetyl Coenzyme A↗
PubMed2001

Expression of Clarkia S-linalool synthase in transgenic petunia plants results in the accumulation of S-linalyl-beta-D-glucopyranoside.

Petunia hybrida W115 was transformed with a Clarkia breweri S-linalool synthase cDNA (lis). Lis was expressed in all tissues analysed, and linalool was detected in leaves, sepals, corolla, stem and ovary, but not in nectaries, roots, pollen and style. However, the S-linalool produced by the plant in the various tissues is not present as free linalool, but was efficiently converted to non-volatile S-linalyl-beta-D-glucopyranoside by the action of endogenous glucosyltransferase. The results presented demonstrate that monoterpene production can be altered by genetic modification, and that the compounds produced can be converted by endogenous enzymatic activity.

Acyclic Monoterpenes↗
PubMed1993

Structural biopolymer preservation in Miocene leaf fossils from the Clarkia site, northern Idaho.

The 17- to 20-million-year-old locality at Clarkia, northern Idaho, is renowned for yielding amplifiable DNA from a magnolia leaf fossil. In-source pyrolysis-mass spectrometry and pyrolysis-gas chromatography/mass spectrometry now reveal that molecular preservation of biomacromolecules is highly selective; structural polysaccharides, cutin polyesters, and proteins were not preserved in detectable quantity in the leaf tissues, whereas both lignin and an aliphatic biopolymer were detected. This study points up the need for improved understanding of the precise modes and extent of preservation of biomacromolecules in fossil materials and sediments.

Journal Article↗
PubMedDate not supplied

A linkage map for CRINKLED PETAL: a homeotic gene of Clarkia tembloriensis (Onagraceae).

Homeotic mutations in flowers lead to the development of floral organs in abnormal locations. In most laboratory-induced examples of this type of mutation, two adjacent whorls of organs are affected, resulting in two whorls of abnormal organ formation. However, the crinkled petal mutant of Clarkia tembloriensis is interesting because it is a naturally occurring mutation and it affects only the second whorl of organs, producing sepaloid petals. In this study one wild-type population (Cantua Creek-2) and one crinkled petal mutant population (Red Rocks) were compared using 181 different primers in random amplified polymorphic DNA (RAPD) analysis. Bulk DNA from each parent population and their subsequent crosses were used to compare the genetic differences between the two populations and to search for molecular markers linked with the CRINKLED PETAL locus. A linkage map was developed for the CRINKLED PETAL gene, and markers were discovered which flanked both sides of the locus.

Chromosome Mapping↗
PubMed1997

A recently silenced, duplicate PgiC locus in Clarkia.

Previous electrophoretic analysis showed that 17 diploid species of the wildflower Clarkia (Onagraceae) have two cytosolic isozymes of phosphoglucose isomerase (PGIC; EC 5.3.1.9), whereas 15 other diploid species have a single PGIC. Molecular studies revealed that the two isozymes in the former species are encoded by duplicate genes, PgiC1 and PgiC2, whereas the single isozyme in the latter is always encoded by PgiC1. Phylogenetic analysis of the nucleotide sequences implied that PgiC2 was silenced four times independently in the genus. Here we describe a psi PgiC2 from C. mildrediae, a species in which only PgiC1 is expressed. The discovery of the psi PgiC2 is significant because it confirms a formal prediction of the phylogenetic analysis. The psi PgiC2 includes 5,039 nucleotides corresponding to 18 of the 23 exons of PgiC, as well as the intervening introns and 3' nontranslated region. The absence of an increase of nucleotide substitutions in its "exons" suggests that the gene was silenced recently. The present study appears to be the first to establish that a specific duplicate gene locus regularly expressed in a group of related plant species has been silenced in one of them. The multiple independent silencings of PgiC2 suggest that it remained functional but inessential in ancestral lineages. We discuss the possibility that PgiC2 may have been preserved in these lineages by selection against mutants causing defective PGIC1-PGIC2 heterodimers.

Base Sequence↗
PubMed2002

Characterization of an acyltransferase capable of synthesizing benzylbenzoate and other volatile esters in flowers and damaged leaves of Clarkia breweri.

A cDNA encoding a protein with 456 amino acids whose sequence shows considerable similarity to plant acyltransferases was identified among 750 Clarkia breweri flower expressed sequence tags. The cDNA was expressed in Escherichia coli, and the protein produced was shown to encode the enzyme benzoyl-coenzyme A (CoA):benzyl alcohol benzoyl transferase (BEBT). BEBT catalyzes the formation of benzylbenzoate, a minor constituent of the C. breweri floral aroma, but it also has activity with a number of other alcohols and acyl CoAs. The BEBT gene is expressed in different parts of the flowers with maximal RNA transcript levels in the stigma, and no expression was observed in the leaves under normal conditions. However, BEBT expression was induced in damaged leaves, reaching a maximum 6 h after damage occurred. We also show here that a closely related tobacco (Nicotiana tabacum) gene previously shown to be induced in leaves after being challenged by phytopathogenic bacteria also has BEBT activity, whereas the most similar protein to BEBT in the Arabidopsis proteome does not use benzoyl CoA as a substrate and instead can use acetyl CoA to catalyze the formation of cis-3-hexen-1-yl acetate, a green-leaf volatile.

Acyltransferases↗
PubMed1997

Floral scent production in Clarkia breweri (Onagraceae). II. Localization and developmental modulation of the enzyme S-adenosyl-L-methionine:(iso)eugenol O-methyltransferase and phenylpropanoid emission.

We have previously shown (R.A. Raguso, E. Pichersky [1995] Plant Syst Evol 194: 55-67) that the strong, sweet fragrance of Clarkia breweri (Onagraceae), an annual plant native to California, consists of 8 to 12 volatile compounds, including 4 phenylpropanoids. Although some C. breweri plants emit all 4 phenylpropanoids (eugenol, isoeugenol, methyleugenol, and isomethyleugenol), other C. breweri plants do not emit the latter 2 compounds. Here we report that petal tissue was responsible for the bulk of the phenylpropanoid emission. The activity of S-adenosyl-L-methionine: (iso)eugenol O-methyltransferase (IEMT), a novel enzyme that catalyzes the methylation of the para-4'-hydroxyl of both eugenol and (iso)eugenol to methyleugenol and isomethyleugenol, respectively, was also highest in petal tissue. IEMT activity was absent from floral tissues of plants not emitting (iso)methyleugenol. A C. breweri cDNA clone encoding IEMT was isolated, and its sequence was shown to have 70% identity to S-adenosyl-L-methionine:caffeic acid O-methyltransferase. The protein encoded by this cDNA can use eugenol and isoeugenol as substrates, but not caffeic acid. Steady-state IEMT mRNA levels were positively correlated with levels of IEMT activity in the tissues, and no IEMT mRNA was observed in flowers that do not emit (iso)methyleugenol. Overall, the data show that the floral emission of (iso)methyleugenol is controlled at the site of emission, that a positive correlation exists between volatile emission and IEMT activity, and that control of the level of IEMT activity is exerted at a pretranslational step.

Amino Acid Sequence↗
PubMed1998

Floral scent production in Clarkia breweri. III. Enzymatic synthesis and emission of benzenoid esters.

The fragrance of Clarkia breweri (Onagraceae), a California annual plant, includes three benzenoid esters: benzylacetate, benzylbenzoate, and methylsalicylate. Here we report that petal tissue was responsible for the benzylacetate and methylsalicylate emission, whereas the pistil was the main source of benzylbenzoate. The activities of two novel enzymes, acetyl-coenzyme A:benzylalcohol acetyltransferase (BEAT), which catalyzes the acetyl esterification of benzylalcohol, and S-adenosyl-L-methionine:salicylic acid carboxyl methyltransferase, which catalyzes the methyl esterification of salicylic acid, were also highest in petal tissue and absent in leaves. In addition, the activity of both enzymes in the various floral organs was developmentally and differentially regulated. S-Adenosyl-L-methionine:salicylic acid carboxyl methyltransferase activity in petals peaked in mature buds and declined during the next few days after anthesis, and it showed a strong, positive correlation with the emission of methylsalicylate. The levels of BEAT activity and benzylacetate emission in petals also increased in parallel as the buds matured and the flowers opened, but as emission began to decline on the 2nd d after anthesis, BEAT activity continued to increase and remained high until the end of the lifespan of the flower.

Acetyltransferases↗
PubMed1996

Evolution of floral scent in Clarkia: novel patterns of S-linalool synthase gene expression in the C. breweri flower.

Flowers of Clarkia breweri, an annual plant from the coastal range of California, emit a strong sweet scent of which S-linalool, an acyclic monoterpene, is a major component. Chromosomal, chemical, and morphological data, and the species' geographic distribution, suggest that C. breweri evolved from an extant nonscented species, C. concinna. A cDNA of Lis, the gene encoding S-linalool synthase, was isolated from C. breweri. We show that in C. breweri, Lis is highly expressed in cells of the transmitting tract of the stigma and style and in the epidermal cells of petals, as well as in stamens, whereas in the nonscented C. concinna, Lis is expressed only in the stigma and at a relatively low level. In both species, changes in protein levels parallel changes in mRNA levels, and changes in enzyme activity levels parallel changes in protein levels. The results indicate that in C. breweri, the expression of Lis has been upregulated and its range enlarged to include cells not expressing this gene in C. concinna. These results show how scent can evolve in a relatively simple way without the evolution of highly specialized "scent glands" and other specialized structures. Lis encodes a protein that is structurally related to the family of proteins termed terpene synthases. The protein encoded by Lis is the first member of this family found to catalyze the formation of an acyclic monoterpene.

Acyclic Monoterpenes↗
PubMed2001

Trade-offs between male and female reproduction associated with allozyme variation in phosphoglucoisomerase in an annual plant (Clarkia unguiculata: Onagraceae).

The genotype of an individual for allozymes such as phosphoglucoisomerase (Pgi) is often not neutral with regard to fitness. Studies of several taxa have found consistent fitness differences among Pgi genotypes expressing different allozymes. We conducted a greenhouse experiment with Clarkia unguiculata to determine whether allelic variation at the Pgi-C1 locus may affect components of male and female function. We found significant differences in siring success between pollen donors homozygous for different Pgi alleles. When a mixture of pollen was applied to stigmas under conditions of gametophytic competition (more pollen deposited on stigmas than there are ovules available to fertilize), donors homozygous for the C allele of Pgi sired more seeds per fruit than B-allele donors. Differences between genotypes with respect to female fertility per fruit contrasted with the male advantage associated with the C allele. Recipients homozygous for the C allele produced fruits with more aborted seeds and fewer viable seeds than recipients homozygous for the B allele. These results suggest that allelic variation at a single locus may have opposing effects on male and female reproductive success in C. unguiculata, and that trade-offs between the two types of reproductive success could contribute to the maintenance of variation at the Pgi-C1 locus.

Animals↗
PubMed1999

Variation among populations of Clarkia Unguiculata (Onagraceae) along altitudinal and latitudinal gradients.

We investigated phenotypic variation in 15 traits in greenhouse-grown plants from 16 populations of Clarkia unguiculata from three elevational habitats and six latitudinal transects. Populations from the lowest and highest elevations were geographically and ecologically marginal within the species' range. We (1) describe patterns of trait variation with elevation and latitude; (2) compare latitutidinal variation between marginal and central areas of the species' range; and (3) compare patterns of variation within C. unguiculata to interspecific patterns within the genus. Although there was some evidence that traits varied clinally (i.e., increased/decreased monotonically) along environmental gradients, interaction effects between altitude and latitude dominated patterns of variation. For most traits, latitudinal trends at the low-elevation margin of the species' range differed from trends at mid- and high-elevation areas. Based on interspecific comparisons, populations at the hotter, more arid ends of both environmental gradients were expected to have rapid development, small flowers and vegetative size, low levels of herkogamy and protandry, and high rates of gas exchange. Instead, we found that while some traits were correlated with one gradient in the expected way (e.g., development time with elevation, gas-exchange physiology with latitude), all traits were not consistently associated with each other along both gradients, and intraspecific patterns of variation differed from interspecific patterns.

Journal Article↗
PubMed2000

Differential siring success of Pgi genotypes in Clarkia Unguiculata (Onagraceae).

Competition among pollen grains for the fertilization of ovules can play an important role in determining the male and female reproductive success of flowering plants. To examine the influence of pollen-donor genotype on male reproductive success, hand-pollinations were conducted on Clarkia unguiculata and the siring success of pollen-donor plants was compared between donors homozygous for different allelomorphs of the allozyme PGI (phosphoglucoisomerase). Donors homozygous for the B allele sired more seeds than C-allele donors. Single-donor crosses indicated that C-donor-sired seeds are aborted more often than are B-donor-sired seeds, suggesting that the B-allele donor's advantage in mixed pollinations was a result of differential abortion. A negative relationship between pollen load and the siring success of B-allele donors implies that pollen from B-allele donors has reduced performance relative to C-allele donors when pollen loads are high. These data demonstrate consistent differences in siring success between individuals homozygous for different alleles at a single locus and suggest that variation at the Pgi locus may be maintained by a post-pollination trade-off.

Journal Article↗
PubMed2001

Size-dependent sex allocation within flowers of the annual herb Clarkia unguiculata (Onagraceae): ontogenetic and among-plant variation.

The relative allocation of resources to male and female functions may vary among flowers within and among individual plants for many reasons. Several theoretical models of sex allocation in plants predict a positive correlation between the resource status of a flower or individual and the proportion of reproductive resources allocated to female function. These models assume that, independent of resource status, a negative correlation exists between male and female investment. Focusing on the allocation of resources within flowers, we tested these theoretical predictions and this assumption using the annual Clarkia unguiculata (Onagraceae). We also sought preliminary evidence for a genetic component to these relationships. From 116 greenhouse-cultivated plants representing 30 field-collected maternal families, multiple flowers and fruits per plant were sampled for gamete production, pollen : ovule ratio, seed number, ovule abortion, seed biomass/fruit, mean individual seed mass, and petal area. If sex allocation changes as predicted, then (1) assuming that flowers produced early have access to more resources than those produced later, basal flowers should exhibit a higher absolute and proportional investment in female function than distal flowers and (2) plants of high resource status (large plants) should produce flowers with a higher proportional investment in female function than those of low resource status. Within plants, variation in floral traits conformed to the first prediction. Among plants and families, no significant effects of plant size (dry stem biomass) on intrafloral proportional sex allocation were observed. We detected no evidence for a negative genetic correlation between male and female investment per flower, even when controlling for plant size.

Journal Article↗
PubMed1995

Population structure of morphological traits in Clarkia dudleyana. I. Comparison of FST between allozymes and morphological traits.

Studies of genetic variation at allozyme loci, assumed to be selectively neutral, have provided valuable insights into the genetic structure of numerous populations. The degree to which population structure of allozyme variation reflects that of quantitative traits, however, is not well resolved. Here, we compare estimates of population differentiation (FST) of 11 populations for allozymes with those for nine discrete and nine continuous morphological traits. Overall, the allozymes have the lowest FST estimates, indicating relatively little population differentiation. Excepting two traits, petal width and long internode length, the continuous morphological traits have estimates similar to those from allozymes. The discrete morphological traits tend to have the highest estimates. On a single trait basis, estimates of FST for four discrete and two continuous traits are higher than those for allozymes. A more detailed (narrow-sense quantitative) genetic study of two populations suggests that these estimates of FST may underestimate the true value because of dominance. Clustering analyses show that the pattern of differentiation for the discrete morphological traits strongly reflects the geographical distribution of the populations, whereas the patterns for the continuous traits and allozymes do not. These results suggest that selection has been occurring on the discrete morphological traits, selecting toward a common optimum within each geographic group, and optima differing among geographic groups.

Cluster Analysis↗