Discovery of insect anti-juvenile hormones in plants.?2U

Terpenoid-based defenses in conifers: cDNA cloning, characterization, and functional expression of wound-inducible (E)-alpha-bisabolene synthase from grand fir (Abies grandis)

(E)-alpha-Bisabolene synthase is one of two wound-inducible sesquiterpene synthases of grand fir (Abies grandis), and the olefin product of this cyclization reaction is considered to be the precursor in Abies species of todomatuic acid, juvabione, and related insect juvenile hormone mimics. A cDNA encoding (E)-alpha-bisabolene synthase was isolated from a wound-induced grand fir stem library by a PCR-based strategy and was functionally expressed in Escherichia coli and shown to produce (E)-alpha-bisabolene as the sole product from farnesyl diphosphate. The expressed synthase has a deduced size of 93.8 kDa and a pI of 5. 03, exhibits other properties typical of sesquiterpene synthases, and resembles in sequence other terpenoid synthases with the exception of a large amino-terminal insertion corresponding to Pro81-Val296. Biosynthetically prepared (E)-alpha-[3H]bisabolene was converted to todomatuic acid in induced grand fir cells, and the time course of appearance of bisabolene synthase mRNA was shown by Northern hybridization to lag behind that of mRNAs responsible for production of induced oleoresin monoterpenes. These results suggest that induced (E)-alpha-bisabolene biosynthesis constitutes part of a defense response targeted to insect herbivores, and possibly fungal pathogens, that is distinct from induced oleoresin monoterpene production.

Plant terpenoid synthases: molecular biology and phylogenetic analysis

This review focuses on the monoterpene, sesquiterpene, and diterpene synthases of plant origin that use the corresponding C10, C15, and C20 prenyl diphosphates as substrates to generate the enormous diversity of carbon skeletons characteristic of the terpenoid family of natural products. A description of the enzymology and mechanism of terpenoid cyclization is followed by a discussion of molecular cloning and heterologous expression of terpenoid synthases. Sequence relatedness and phylogenetic reconstruction, based on 33 members of the Tps gene family, are delineated, and comparison of important structural features of these enzymes is provided. The review concludes with an overview of the organization and regulation of terpenoid metabolism, and of the biotechnological applications of terpenoid synthase genes.

Juvenile hormone regulates the expression of the gene encoding ceratotoxin a, an antibacterial peptide from the female reproductive accessory glands of the medfly Ceratitis capitata

Ceratotoxin A is an antibacterial peptide produced by the reproductive female accessory glands of the medfly Ceratitis capitata. To investigate whether ceratotoxin A gene expression was affected by juvenile hormone, which has gonadotropic functions in adult insects, newly emerged female medflies were treated with precocene II, an antiallotropin compound capable of inhibiting juvenile hormone biosynthesis. Daily treatment of newly emerged flies with precocene II blocked ceratotoxin A gene expression in a dose-dependent manner. Ceratotoxin A gene expression could be recovered after withdrawl of precocene II treatment. Moreover, the effect of precocene II on ceratotoxin A gene expression could be countered by simultaneous treatment with methoprene, a juvenile hormone analogue. The effects of precocene II and methoprene treatments on the growth of both ovaries and accessory glands was also investigated. Our data suggest that ceratotoxin A gene expression is modulated by juvenile hormone.

Biomorphological alterations induced by an anti-juvenile hormonal compound, 2-(2-ethoxyethoxy)ethyl furfuryl ether, on three species of triatominae larvae (Hemiptera, Reduviidae)

Applied topically to larvae of Rhodnius prolixus Stal, Triatoma infestans (Klug) and Panstrongylus herreri Wygodzinsky, vectors of Trypanosoma cruzi, the causative agent of Chagas' disease, a synthetic, furan-containing anti-juvenile hormonal compound, 2-(2-ethoxyethoxy)ethyl furfuryl ether induced a variety of biomorphological alterations, including precocious metamorphosis into small adultoids with adult abdominal cuticle, ocelli, as well as rudimentary adultoid wings. Some adultoids died during ecdysis and were confined within the old cuticle. The extension of these biomorphological responses is discussed in terms of the complexity of the action of anti-juvenile hormonal compounds during the development of triatomines.

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 analysis of the Methoprene-tolerant gene region of Drosophila melanogaster

Adult functions of juvenile hormone (JH) have been described for Drosophila melanogaster and other dipteran insects, but preadult function for this hormone remains largely unknown in this order of insects. We have identified a mutation of Drosophila, Methoprene-tolerant (Met), which appears to alter JH reception during late larval development. The molecular cloning of Met will be a step toward understanding this gene and possibly identifying a preadult role(s) for JH. Molecular cloning was initiated using the technique of transposon-tagging with a transposable P element. P-element insertional alleles of Met were generated, and genomic libraries were constructed from two of these alleles. From these libraries P-element-bearing clones were isolated that in situ hybridized to the cytogenetic region where Met had been previously localized by genetic methods. Two of the alleles were shown to have complete P-elements inserted in similar, but not identical, locations in the predicted cytogenetic region where Met is located. A late-larval cDNA library was screened to identify transcriptional units in this region, and clones were recovered with homology to a DNA fragment abutting the P-element insertion site. These clones may represent Met cDNA molecules.

Effects of precocene analogs on the nematode Caenorhabditis remanei (var. Bangaloreiensis). I. Structure/activity relations

Precocenes (PI and PII) and 114 of their analogs (PAs) were synthetized and tested on C. remanei embryos for their precocene-like (P-like) activities resulting in unusual development at sublethal doses. The P-like activity was quantitated by plotting the probit of the percentage of the developmentally affected survivors against the (log) dose to obtain the EC plot and the half effective concentration (EC50). All five PAs (PI, PII, 7-ethoxy-PII, 7-(prop-2-ynyloxy)-PI, and 6-methoxy-7-(prop-2-ynyloxy)-PII) which exert both antiallatal activity in insects and P-like activity in nematodes are 7-alkoxy-substituted 2,2-dimethylchromenes. Both activities can be enhanced by an additional 6-MeO-substitution or by an asymmetric 6,7-dialkoxy-substitution, on condition that R-7 is longer than R-6. There are many more similarities than dissimilarities in the structural requirements needed for antiallatal and P-like activities. All but three nonantiallatal PAs effective in nematodes are 7-prop-2-ynyloxy-subsituted; two are symmetrically 6,7-disubstituted, and one is heterosubstituted (thio-PI). All PAs with antiallatal but without P-like activity are 7-monosubstituted with a relatively long alkoxy group. Certain substitutions favor antiallatal activity and others P-like activity. The severe nematocidal effect of 6,7-methylenedioxy-2,2-dimethylchromene (inert in insects) is not accompanied by P-like activity. The present findings lend some indirect support to the supposition that JH-producing cells and/or JH-dependent function(s) might exist in the nematodes.

Alteration of precocene II-induced hepatotoxicity by modulation of hepatic glutathione levels

Precocene II (6,7-dimethoxy-2,2-dimethyl-2H-benzo[b]pyran), an insect growth regulator that is structurally related to several naturally occurring carcinogenic and non-carcinogenic alkenylbenzenes, is genotoxic and produces hepatic centrolobular necrosis in rats. This investigation was conducted to evaluate the effects of modulation of hepatic glutathione levels on the toxicity of precocene II. Administration of a toxic dose of precocene II (175 mg/kg) to male Sprague-Dawley rats rapidly depleted hepatic GSH, produced histopathological changes in the liver, and induced increases in serum aminotransferase activity. Concurrent administration of the cysteine pro-drug L-2-oxothiazolidine-4-carboxylic acid (OTC) prevented these toxic effects of precocene II. In contrast, pretreatment of rats with DL-buthionine-SR-sulfoximine (BSO), an inhibitor of glutathione synthesis, potentiated the toxicity of an otherwise non-toxic dose of precocene II (100 mg/kg). These results indicate that glutathione is important for protection from precocene II-induced hepatotoxicity.

Microbial transformation of precocene II: oxidative reactions by Streptomyces griseus

Various species of "Streptomyces," "Aspergillus," "Rhodotorula," "Brevilegnia," "Syncephalastrum," and "Stysanus" were found to transform precocene II to three major metabolites. These major biotransformation products were isolated from a preparative-scale incubation of precocene II with Streptomyces griseus and were conclusively identified as (-)cis- and (+)trans-precocene II-3,4-dihydrodiols and (+)-3-chromenol. 18O2 incorporation studies indicated the involvement of a monooxygenase enzyme system in precocene II transformation by S. griseus. A mechanism is proposed for the formation of (+)-3-chromenol.

Hepatotoxicity of precocene I in rats. Role of metabolic activation in vivo

The mechanism of the hepatotoxicity of precocene I has been investigated in male, Sprague-Dawley rats. Administration of a single dose of precocene I caused a large depletion of liver glutathione (GSH) levels that was both time and dose dependent. Concomitant with the decrease of liver GSH, there was an increase in serum glutamic pyruvic transaminase (GPT) levels which was also time and dose dependent. Administration of a single dose of [4-3H]precocene I resulted in extensive covalent binding of the radiolabel to liver proteins and DNA in the liver; the extent of binding increased with increasing dose. Treatment of the rats with the mixed-function oxidase inhibitor piperonyl butoxide, before administration of precocene I, significantly decreased the proportion of the radiolabel bound covalently to proteins and DNA, although the total radioactivity (bound and unbound) in the liver remained the same. Piperonyl butoxide pretreatment limited both the liver GSH depletion and the hepatic necrosis normally caused by precocene I. These results are consistent with the view that the hepatotoxicity of precocene I is due to reactive metabolites formed through cytochrome P-450 mediated metabolism of precocene I.

Insecticide metabolism and selective toxicity

Current research is focused on means to improve the environmental acceptability and selective toxicity of existing classes of insecticides and the search for new and species selective modes of insecticidal action. The study of species differences in metabolism and its modulation by changes in chemical structure is a vital component of this effort. The importance of metabolism is illustrated by examples from the major classes of insect control chemicals, namely organophosphorus and carbamate insecticides, DDT, pyrethroids and insect growth regulators.

Metabolism and bioconversion of chromene derivatives inAgeratina adenophora (Asteraceae)

Seedlings ofAgeratina adenophora accumulate the chromenes demethoxyencecalin, encecalin and demethylencecalin. More than 80% of the total chromenes within the seedling are confined to the leaves where they are stored within the mesophyll. Metabolism of the chromenes during development of the seedlings was subjected to analysis by high-performance liquid chromatography. The accumulation kinetics obtained, as well as feeding experiments with non-radioactive chromenes, showed the bioconversion of these compounds to proceed from demethoxyencecalin via hydroxylation yielding demethylencecalin, followed by methylation yielding encecalin. Inhibitor studies with glyphosate indicate that the chromenes arise from precursors derived from the shikimic-acid pathway.

Induction of DNA damage and repair synthesis in freshly isolated rat hepatocytes by the proallatocidin precocene II

The proallatocidin precocene II (6,7-dimethoxy-2,2-dimethyl-2H-benzo-[b]pyran) has previously been shown to induce centrolobular liver necrosis. Here we have examined the ability of precocene II to produce DNA damage in suspensions of freshly isolated rat hepatocytes using the alkaline elution technique with N-methyl-N'-nitro-N-nitrosoguanidine as a positive control. At concentrations (10(-4)-10(-5) M) which did not induce cytotoxicity as judged by the leakage of glutamic-oxaloacetic transaminase, precocene II was capable of producing DNA single-strand breaks. In addition, a dose-dependent DNA repair synthesis (unscheduled DNA synthesis, UDS) was detected in hepatocytes exposed to precocene II. The induction of UDS was measured by incorporation of [3H]thymidine into purified hepatic DNA via a membrane filter retention method and liquid scintillation counting. Hence, results obtained in the present study indicate the potential genotoxicity of precocene II and the utility of DNA damage and repair assays in genetic toxicology.