Characterization of a Glyphosate-Tolerant Enzyme from Streptomyces svecius: A Distinct Class of 5-Enolpyruvylshikimate-3-phosphate Synthases

Natural and modified versions of the 5-enolpyruvylshikimate-3-phosphate synthase (epsps) gene have been used to confer tolerance to the broad-spectrum herbicide glyphosate in a variety of commercial crops. The most widely utilized trait was obtained from the Agrobacterium tumefaciens strain CP4 and has been commercialized in several glyphosate-tolerant crops. The EPSPS gene products are enzymes that have been divided into three classes based on sequence similarity, sensitivity to glyphosate, and steady-state catalytic parameters. Herein, we describe the informatics-guided identification and biochemical and structural characterization of a novel EPSPS from Streptomyces sviceus (DGT-28 EPSPS). The data suggest DGT-28 EPSPS and other closely related homologues exemplify a distinct new class (Class IV) of EPSPS enzymes that display intrinsic tolerance to high concentrations of glyphosate (Ki ≥ 5000 μM). We further demonstrate that dgt-28 epsps, when transformed into stable plants, provides robust (≥4× field rates) vegetative/reproductive herbicide tolerance and has utility in weed-control systems comparable to that of commercialized events.

Corteva Agriscience's perspective and commitment to managing herbicide resistance

Chemical weed control has been widely adopted and has led to increased efficiency and reduced crop production costs. With the increased use of herbicides and the introduction of herbicide-tolerant crops we have also seen an increase in herbicide resistant weeds which presents a challenge for farmers and land managers. It is incumbent upon the agriculture industry to be an indispensable partner in leading policy, research, education, and best management practices related to herbicide resistance. Corteva Agriscience is an active, engaged partner in herbicide resistance research, education, and communication globally to enable the long-term sustainable use of herbicide-tolerant crop traits and herbicides. Some of the key components of our commitment are highlighted in this Perspective paper and include memberships, partnerships, close involvement with CropLife International (and regional CropLife organizations), and Herbicide Resistance Action Committees at the Global, regional and country level, technical leadership and engagement in multiple scientific societies, and collaboration with universities and research institutes. Corteva is committed to advancing sustainable agriculture to enrich lives and our planet for generations to come and this drives our action through the entire product lifecycle and with our customers and consumers.

Transcription Terminator-Mediated Enhancement in Transgene Expression in Maize: Preponderance of the AUGAAU Motif Overlapping With Poly(A) Signals

The selection of transcription terminators (TTs) for pairing with high expressing constitutive promoters in chimeric constructs is crucial to deliver optimal transgene expression in plants. In this study, the use of the native combinations of four polyubiquitin gene promoters and corresponding TTs resulted in up to >3-fold increase in transgene expression in maize. Of the eight polyubiquitin promoter and TT regulatory elements utilized, seven were novel and identified from the polyubiquitin genes of Brachypodium distachyon, Setaria italica, and Zea mays. Furthermore, gene expression driven by the Cassava mosaic virus promoter was studied by pairing the promoter with distinct TTs derived from the high expressing genes of Arabidopsis. Of the three TTs studied, the polyubiquitin10 gene TT produced the highest transgene expression in maize. Polyadenylation patterns and mRNA abundance from eight distinct TTs were analyzed using 3'-RACE and next-generation sequencing. The results exhibited one to three unique polyadenylation sites in the TTs. The poly(A) site patterns for the StPinII TT were consistent when the same TT was deployed in chimeric constructs irrespective of the reporter gene and promoter used. Distal to the poly(A) sites, putative polyadenylation signals were identified in the near-upstream regions of the TTs based on previously reported mutagenesis and bioinformatics studies in rice and Arabidopsis. The putative polyadenylation signals were 9 to 11 nucleotides in length. Six of the eight TTs contained the putative polyadenylation signals that were overlaps of either canonical AAUAAA or AAUAAA-like polyadenylation signals and AUGAAU, a top-ranking-hexamer of rice and Arabidopsis gene near-upstream regions. Three of the polyubiquitin gene TTs contained the identical 9-nucleotide overlap, AUGAAUAAG, underscoring the functional significance of such overlaps in mRNA 3' end processing. In addition to identifying new combinations of regulatory elements for high constitutive trait gene expression in maize, this study demonstrated the importance of TTs for optimizing gene expression in plants. Learning from this study could be applied to other dicotyledonous and monocotyledonous plant species for transgene expression. Research on TTs is not limited to transgene expression but could be extended to the introduction of appropriate mutations into TTs via genome editing, paving the way for expression modulation of endogenous genes.

Molecular basis for enantioselective herbicide degradation imparted by aryloxyalkanoate dioxygenases in transgenic plants

The synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) is an active ingredient of thousands of commercial herbicides. Multiple species of bacteria degrade 2,4-D via a pathway initiated by the Fe(II) and α-ketoglutarate (Fe/αKG)-dependent aryloxyalkanoate dioxygenases (AADs). Recently, genes encoding 2 AADs have been deployed commercially in herbicide-tolerant crops. Some AADs can also inactivate chiral phenoxypropionate and aryloxyphenoxypropionate (AOPP) herbicides, albeit with varying substrate enantioselectivities. Certain AAD enzymes, such as AAD-1, have expanded utility in weed control systems by enabling the use of diverse modes of action with a single trait. Here, we report 1) the use of a genomic context-based approach to identify 59 additional members of the AAD class, 2) the biochemical characterization of AAD-2 from Bradyrhizobium diazoefficiens USDA 110 as a catalyst to degrade (S)-stereoisomers of chiral synthetic auxins and AOPP herbicides, 3) spectroscopic data that demonstrate the canonical ferryl complex in the AAD-1 reaction, and 4) crystal structures of representatives of the AAD class. Structures of AAD-1, an (R)-enantiomer substrate-specific enzyme, in complexes with a phenoxypropionate synthetic auxin or with AOPP herbicides and of AAD-2, which has the opposite (S)-enantiomeric substrate specificity, reveal the structural basis for stereoselectivity and provide insights into a common catalytic mechanism.

Weed resistance to synthetic auxin herbicides

Herbicides classified as synthetic auxins have been most commonly used to control broadleaf weeds in a variety of crops and in non-cropland areas since the first synthetic auxin herbicide (SAH), 2,4-D, was introduced to the market in the mid-1940s. The incidence of weed species resistant to SAHs is relatively low considering their long-term global application with 30 broadleaf, 5 grass, and 1 grass-like weed species confirmed resistant to date. An understanding of the context and mechanisms of SAH resistance evolution can inform management practices to sustain the longevity and utility of this important class of herbicides. A symposium was convened during the 2nd Global Herbicide Resistance Challenge (May 2017; Denver, CO, USA) to provide an overview of the current state of knowledge of SAH resistance mechanisms including case studies of weed species resistant to SAHs and perspectives on mitigating resistance development in SAH-tolerant crops. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A combinatorial bidirectional and bicistronic approach for coordinated multi-gene expression in corn

Transgene stacking in trait development process through genetic engineering is becoming complex with increased number of desired traits and multiple modes of action for each trait. We demonstrate here a novel gene stacking strategy by combining bidirectional promoter (BDP) and bicistronic approaches to drive coordinated expression of multi-genes in corn. A unidirectional promoter, Ubiquitin-1 (ZMUbi1), from Zea mays was first converted into a synthetic BDP, such that a single promoter can direct the expression of two genes from each end of the promoter. The BDP system was then combined with a bicistronic organization of genes at both ends of the promoter by using a Thosea asigna virus 2A auto-cleaving domain. With this gene stacking configuration, we have successfully obtained expression in transgenic corn of four transgenes; three transgenes conferring insect (cry34Ab1 and cry35Ab1) and herbicide (aad1) resistance, and a phiyfp reporter gene using a single ZMUbi1 bidirectional promoter. Gene expression analyses of transgenic corn plants confirmed better coordinated expression of the four genes compared to constructs driving each gene by independent unidirectional ZmUbi1 promoter. To our knowledge, this is the first report that demonstrates application of a single promoter for co-regulation of multiple genes in a crop plant. This stacking technology would be useful for engineering metabolic pathways both for basic and applied research.

Robust crop resistance to broadleaf and grass herbicides provided by aryloxyalkanoate dioxygenase transgenes

Engineered glyphosate resistance is the most widely adopted genetically modified trait in agriculture, gaining widespread acceptance by providing a simple robust weed control system. However, extensive and sustained use of glyphosate as a sole weed control mechanism has led to field selection for glyphosate-resistant weeds and has induced significant population shifts to weeds with inherent tolerance to glyphosate. Additional weed control mechanisms that can complement glyphosate-resistant crops are, therefore, urgently needed. 2,4-dichlorophenoxyacetic acid (2,4-D) is an effective low-cost, broad-spectrum herbicide that controls many of the weeds developing resistance to glyphosate. We investigated the substrate preferences of bacterial aryloxyalkanoate dioxygenase enzymes (AADs) that can effectively degrade 2,4-D and have found that some members of this class can act on other widely used herbicides in addition to their activity on 2,4-D. AAD-1 cleaves the aryloxyphenoxypropionate family of grass-active herbicides, and AAD-12 acts on pyridyloxyacetate auxin herbicides such as triclopyr and fluroxypyr. Maize plants transformed with an AAD-1 gene showed robust crop resistance to aryloxyphenoxypropionate herbicides over four generations and were also not injured by 2,4-D applications at any growth stage. Arabidopsis plants expressing AAD-12 were resistant to 2,4-D as well as triclopyr and fluroxypyr, and transgenic soybean plants expressing AAD-12 maintained field resistance to 2,4-D over five generations. These results show that single AAD transgenes can provide simultaneous resistance to a broad repertoire of agronomically important classes of herbicides, including 2,4-D, with utility in both monocot and dicot crops. These transgenes can help preserve the productivity and environmental benefits of herbicide-resistant crops.

Direct measurements of Ab and Ac using vertex and kaon charge tags at the SLAC detector

Exploiting the manipulation of the SLAC Linear Collider electron-beam polarization, we present precise direct measurements of the parity-violation parameters A(c) and A(b) in the Z-boson-c-quark and Z-boson-b-quark coupling. Quark-antiquark discrimination is accomplished via a unique algorithm that takes advantage of the precise SLAC Large Detector charge coupled device vertex detector, employing the net charge of displaced vertices as well as the charge of kaons that emanate from those vertices. From the 1996-1998 sample of 400 000 Z decays, produced with an average beam polarization of 73.4%, we find A(c)=0.673+/-0.029(stat)+/-0.023(syst) and A(b)=0.919+/-0.018(stat)+/-0.017(syst).

Improved direct measurement of the parity-violation parameter Ab using a mass tag and momentum-weighted track charge

We present an improved direct measurement of the parity-violation parameter A(b) in the Z boson-b-quark coupling using a self-calibrating track-charge technique applied to a sample enriched in Z-->bb events via the topological reconstruction of the B hadron mass. Manipulation of the Stanford Linear Collider electron-beam polarization permits the measurement of A(b) to be made independently of other Z-pole coupling parameters. From the 1996-1998 sample of 400,000 hadronic Z decays, produced with an average beam polarization of 73.4%, we find A(b)=0.906+/-0.022(stat)+/-0.023(syst).

Improved direct measurement of A(b) and A(c) at the Z(0) pole using a lepton tag

The parity violation parameters A(b) and A(c) of the Zb(b) and Zc(c) couplings have been measured directly, using the polar angle dependence of the polarized cross sections at the Z(0) pole. Bottom and charmed hadrons were tagged via their semileptonic decays. Both the electron and muon analyses take advantage of new multivariate techniques to increase the analyzing power. Based on the 1993-1998 SLD sample of 550,000 Z(0) decays produced with highly polarized electron beams, we measure A(b) = 0.919+/-0.030(stat)+/-0.024(syst), and A(c) = 0.583+/-0.055(stat)+/-0.055(syst).

Improved direct measurement of leptonic coupling asymmetries with polarized Z bosons

We present final measurements of the Z boson-lepton coupling asymmetry parameters A(e), A(mu), and A(tau) with the complete sample of polarized Z bosons collected by the SLD detector at the SLAC Linear Collider. From the left-right production and decay polar angle asymmetries in leptonic Z decays we measure A(e) = 0.1544+/-0.0060, A(mu) = 0.142+/-0.015, and A(tau) = 0.136+/-0.015. Combined with our left-right asymmetry measured from hadronic decays, we find A(e) = 0.1516+/-0.0021. Assuming lepton universality, we obtain a combined effective weak mixing angle of sin (2)theta(eff)(W) = 0.230 98+/-0.000 26.

First symmetry tests in polarized Z0 decays to bbg

We have made the first direct symmetry tests in the decays of polarized Z0 bosons into fully identified bbg states, collected in the SLD experiment at SLAC. We searched for evidence of parity violation at the bbg vertex by studying the asymmetries in the b-quark polar- and azimuthal-angle distributions, and for evidence of T-odd, CP-even or CP-odd, final-state interactions by measuring angular correlations between the three-jet plane and the Z0 polarization. We found results consistent with standard model expectations and set 95% C. limits on anomalous contributions.

The catecholamines up (Catsup) protein of Drosophila melanogaster functions as a negative regulator of tyrosine hydroxylase activity

We report the genetic, phenotypic, and biochemical analyses of Catecholamines up (Catsup), a gene that encodes a negative regulator of tyrosine hydroxylase (TH) activity. Mutations within this locus are semidominant lethals of variable penetrance that result in three broad, overlapping effective lethal phases (ELPs), indicating that the Catsup gene product is essential throughout development. Mutants from each ELP exhibit either cuticle defects or catecholamine-related abnormalities, such as melanotic salivary glands or pseudotumors. Additionally, Catsup mutants have significantly elevated TH activity that may arise from a post-translational modification of the enzyme. The hyperactivation of TH in Catsup mutants results in abnormally high levels of catecholamines, which can account for the lethality, visible phenotypes, and female sterility observed in these mutants. We propose that Catsup is a component of a novel system that downregulates TH activity, making Catsup the fourth locus found within the Dopa decarboxylase (Ddc) gene cluster that functions in catecholamine metabolism.

The Wilhelmine E. Key 1992 Invitational lecture. Phenotypic analysis of the Dopa decarboxylase gene cluster mutants in Drosophila melanogaster

Mutations in a majority of the 18 loci of the Dopa decarboxylase (Ddc) gene cluster effect similar morphological defects of the cuticle and/or catecholamine-related abnormalities. Mutations in 14 loci affect cuticle formation, cuticle sclerotization, or cuticle melanization, with mutations in 11 of these same loci (including Ddc and amd) producing melanotic psueudotumors, symptomatic, perhaps, of abnormal catecholamine metabolism. Mutations in seven of the genes perturb catecholamine pool levels during prepupal and pupal development, all of which also form melanotic pseudotumors, suggesting several of these genes may encode proteins involved in catecholamine metabolism. Thus, the Ddc gene cluster represents in higher eukaryotes an unusual example of a large cluster of functionally related genes involved in a common physiological process.

Catecholamine metabolism and in vitro induction of premature cuticle melanization in wild type and pigmentation mutants of Drosophila melanogaster

The major pathway leading to adult cuticle melanization in Drosophila melanogaster has been investigated by a combination of biochemical and genetic approaches. By comparing catecholamine pools in newly emerged flies and in frass (excreta) collected 1 to 4 days after eclosion from wild type with those obtained from several pigmentation mutants, the major flow of catecholamines through the pathway to an unidentified final catabolite was determined. We also demonstrate that incubation with dopamine in vitro induces premature melanization in wild type unpigmented pharate adults several hours before the developmentally programmed onset of melanization, supporting the hypothesis that the availability of catecholamines may be the limiting factor determining the onset of melanization and that the major enzymatic activities that act downstream of dopa decarboxylase in the pathway are deposited into the cuticle before pigmentation begins. In vitro melanization studies with various pigmentation mutants that are associated with critical enzymatic steps in Drosophila catecholamine metabolism are consistent with their proposed function and suggest a central role of N-beta-alanyldopamine in adult cuticle pigmentation.

The genetic and molecular organization of the Dopa decarboxylase gene cluster of Drosophila melanogaster

We report the complete molecular organization of the Dopa decarboxylase gene cluster. Mutagenesis screens recovered 77 new Df(2L)TW130 recessive lethal mutations. These new alleles combined with 263 previously isolated mutations in the cluster to define 18 essential genes. In addition, seven new deficiencies were isolated and characterized. Deficiency mapping, restriction fragment length polymorphism (RFLP) analysis and P-element-mediated germline transformation experiments determined the gene order for all 18 loci. Genomic and cDNA restriction endonuclease mapping, Northern blot analysis and DNA sequencing provided information on exact gene location, mRNA size and transcriptional direction for most of these loci. In addition, this analysis identified two transcription units that had not previously been identified by extensive mutagenesis screening. Most of the loci are contained within two dense subclusters. We discuss the effectiveness of mutagens and strategies used in our screens, the variable mutability of loci within the genome of Drosophila melanogaster, the cytological and molecular organization of the Ddc gene cluster, the validity of the one band-one gene hypothesis and a possible purpose for the clustering of genes in the Ddc region.

Temporal and spatial expression of the yellow gene in correlation with cuticle formation and dopa decarboxylase activity in Drosophila development

The yellow (y) gene of Drosophila is required for the formation of black melanin and its deposition in the cuticle. We have studied by immunohistochemical methods the temporal and spatial distribution of the protein product of the y gene during embryonic and pupal development and have correlated its expression with events of cuticle synthesis by the epidermal cells and with cuticle sclerotization. Except for expression in early embryos, the y protein is only found in the epidermal cells and may be secreted into the cuticle as it is being deposited. The amount of y protein in various regions of the embryo and pupa correlates directly with the intensity of melanization over any section of the epidermis. Expression of the y gene begins in the epidermal cells at 48 hr after pupariation and is well correlated with the beginning deposition of the adult cuticle. At this stage the adult cuticle is unsclerotized and unpigmented and dopa decarboxylase levels, a key enzyme in catecholamine metabolism which provides the crosslinking agents as well as the precursors for melanin, is low. As a separate event 26 hr after the onset of y gene expression, the first melanin deposition occurs in the head bristles and pigmentation continues in an anterior to posterior progression until eclosion. This melanization wave is correlated with elevated dopa decarboxylase activity. Crosslinking of the adult cuticle also occurs in a similar anterior to posterior progression at about the same time. We have shown by imaginal disc transplantation that timing of cuticle sclerotization depends on the position of the tissue along the anterior-posterior axis and that it is not an inherent feature of the discs themselves. We suggest that actual melanization and sclerotization of the cuticle by crosslinking are initiated at this time in pupal development by the availability of the catecholamine substrates which diffuse into the cuticle. Intensity of melanization and position of melanin pigment is determined by the presence or absence of the y protein in the cuticle, thus converting the y protein prepattern into the melanization pattern.

Drosophila melanogaster diphenol oxidase A2: gene structure and homology with the mouse mast-cell tum- transplantation antigen, P91A

The Drosophila melanogaster diphenol oxidase (DOX) A2-encoding gene (Dox-A2) is involved in catecholamine metabolism, melanin formation and sclerotization of the cuticle. Insect phenol oxidases (POX) are well studied biochemically, but not genetically and molecularly. The Dox-A2 (2-53.9) gene is the first insect POX-encoding gene to be cloned and sequenced. It encodes a protein product unique among currently known POX. The deduced protein, however, exhibits extensive similarity (58-81%) to the mouse mast cell tum- antigen, P91A [Lurquin et al., Cell 58 (1989) 293-303] and may identify the normal mouse protein as a DOX.

Mutations affecting phenol oxidase activity in Drosophila: quicksilver and tyrosinase-1

The complex enzyme phenol oxidase plays a major role in sclerotization and melanization of cuticle in insects. Production of active enzyme from the inactive proenzyme involves at least six protein components in Drosophila. We examine here the biochemical phenotype of two loci that affect phenol oxidase activity--quicksilver (qs; 1-39.5) and tyrosinase-1 (tyr-1; 2-54.5). Three mutations isolated by different procedures in three different laboratories are alleles at the quicksilver locus. The effects of these mutations have been monitored by means of enzyme assays in vitro and in polyacrylamide gels and by measurement of catecholamine pool sizes. The activity of all three active enzyme components (A1, A2, and A3) is reduced in qs mutants. The activated enzyme of one qs allele is thermolabile, while its activator is normal. Deletion and genetic mapping place tyr-1 near purple (pr; 2-54.5). Enzyme activity is reduced to 10% of normal but is not thermolabile and the activator is normal. The activity of all three A components is reduced. The diphenol oxidase activity in double mutant combinations shows that these mutations and Dox-A2 (Pentz et al., 1986) affect this enzyme in different ways.

Characterization of third chromosome dominant alpha-methyl dopa resistant mutants (Tcr) and their interactions with l(2)amd alpha-methyl dopa hypersensitive alleles in Drosophila melanogaster

In Drosophila melanogaster two alleles at the Third chromosome resistance locus (Tcr; 3-39-6) were isolated in a screen of EMS mutagenized third chromosomes for dominant resistance to dietary alpha-methyl dopa, alpha-MD, a structural analogue of DOPA. Both alleles of Tcr are recessive lethals exhibiting partial complementation. Almost half (48.3%) of the Tcr40/Tcr45 heterozygotes die as embryos but some survive past adult eclosion. Both the embryonic lethal phenotype and the adult phenotype suggest that Tcr is involved in cuticle synthesis. Tcr mutants suppress the lethality of partially complementing alleles at the alpha-MD hypersensitive locus, l(2)amd. The viability of Tcr40/Tcr45, however, is not increased by the presence of a l(2)amd allele. The possibility that the Tcr and l(2)amd mutations reveal a catecholamine metabolic pathway involved in cuticle structure is discussed.

Isolation and characterization of dominant female sterile mutations of Drosophila melanogaster. II. Mutations on the second chromosome

Twenty-four, second chromosome, dominant female sterile (Fs) mutations in Drosophila are described. Fs(2) were isolated at a frequency of approximately 1 per 1000 EMS-treated chromosomes screened. In comparison the isolation of frequency for second chromosome zygotic recessive lethal mutations was approximately 550 per 1000. Complementation analysis of the Fs(2) revertants showed that the 24 Fs(2) mutations identify 13-15 loci, calculated to be about 65-75% of the second chromosome genes EMS mutable to dominant female sterility. Two of the Fs(2) mutations are useful tools for the dominant female sterile technique: Fs(2)1 for induction and detection of germ-line clones and Fs(2)Ugra for follicle cell clones. Several of the Fs(2) mutations bring about novel mutant phenotypes. Seven of them alter egg shape, whereas the others arrest development primarily at two stages: around fertilization by five Fs(2) and during cleavage divisions [by Fs(2) in three loci]. The remaining that allow development to the larval stage of differentiation include four new dorsal alleles and one dominant torso allele. Analysis of germ-line chimeras revealed that with two exceptions all the Fs(2) mutations are germ-line dependent. The Fs(2) mutations were mapped mainly on the basis of mitotic recombination induced in the female germ-line cells of adult females. That most of the Fs(2) may be gain-of-function mutations is indicated by the unusual behavior of the Fs+ germ-line clones and also by the fact that 90% of the could be induced to revert.

The alpha methyl dopa hypersensitive gene, 1(2)amd, and two adjacent genes in Drosophila melanogaster: physical location and direct effects of amd on catecholamine metabolism

The dopa decarboxylase gene (Ddc) is located in a very dense cluster of genes many of whose functions appear to be related to the physiological role of dopa decarboxylase (DDC) in catecholamine metabolism. In Drosophila melanogaster catecholamine metabolism is involved in the production of neurotransmitters and in the synthesis of cross-linking agents for cuticular sclerotization. In this report we consider three loci near Ddc that affect cuticle formation. The alpha methyl dopa hypersensitive gene, 1(2)amd, is definitively assigned to a transcriptional unit 2 kb distal to Ddc. The assignment of 1(2) 37 Bd and 1(2)37 Cc to coding regions in the immediate vicinity of amd and Ddc is examined. amd+ gene activity performs a vital function essential for the formation of insect cuticle and also determines the level of sensitivity to the DDC analogue inhibitor, alpha methyl dopa. We present data that provide direct evidence that the amd+ gene product is required for a step in the metabolism of dopa to one or more novel catecholamines involved in the colorless sclerotization of cuticle.

DdcDE1, a mutant differentially affecting both stage and tissue specific expression of dopa decarboxylase in Drosophila

The isolation and characterization of a unique Dopa decarboxylase (Ddc) mutant in Drosophila melanogaster is reported. This mutant, DdcDE1, exhibits stage- and tissue-specific altered Ddc expression. Homozygous DdcDE1 embryos, central nervous systems (CNSs) at pupariation and newly eclosed adult epidermis all have approximately 5% as much specific dopa decarboxylase (DDC) activity as the pr control stock in which DdcDE1 was induced. In contrast, the DdcDE1 epidermis at pupariation has roughly 50% as much DDC activity as controls, a 10-fold increase over the relative activity detected in other tissues and stages. Although the adult cuticle lacks proper pigmentation as expected in flies with low DDC activity (less than or equal to 5%), the bristles unexpectedly have wild-type black pigmentation. This implies that the bristle forming cells have more DDC activity than the rest of the adult epidermis. This variegated phenotype, black bristles and pale cuticle, plus the fact that DdcDE1 was originally isolated in a reciprocal translocation between proximal X heterochromatin and the euchromatic left arm of the second chromosome, 42 bands from the Ddc locus, suggested that the mutant might be an example of position-effect variegation. All tests for position-effect variegation, including persistence of the mutant phenotype when DdcDE1 was removed from the translocation, were negative. At pupariation DDC cross-reacting material (CRM) levels are similar in DdcDE1 and wild-type controls, but in newly eclosed adults CRM levels are approximately 35% of wild-type controls. This suggests that DDC produced by DdcDE1 adults has less activity per DDC molecule than the DDC produced at pupariation by DdcDE1. If the DDC enzyme produced by DdcDE1 at adult eclosion had full DDC activity (35% DDC CRM = 35% DDC activity) then no mutant phenotype would be exhibited by DdcDE1 since flies with as little as 10% activity have a wild-type phenotype. DDC thermolability assays clearly demonstrate that DDC from DdcDE1 is more thermolabile than control DDC at both pupariation and adult eclosion. Furthermore, DDC from adults in both DdcDE1 and the pr control is more thermolabile than DDC from white prepupae. Mixing experiments indicate the difference in DDC thermolability between pr white prepupae and pr adults is not due to a difference in the white prepupal and adult supernatants. This suggests that in wild-type different isoforms of DDC are produced either by differences in post-translational modification or as a result of a different primary amino acid sequence.(ABSTRACT TRUNCATED AT 400 WORDS)

A diphenol oxidase gene is part of a cluster of genes involved in catecholamine metabolism and sclerotization in drosophila. I. Identification of the biochemical defect in Dox-A2 [l(2)37Bf] mutants

Phenol oxidase, a complex enzyme, plays a major role in the processes of sclerotization and melanization of cuticle in insects. Several loci have been reported to affect levels of phenol oxidase activity, but to date only one structural locus has been identified [Dox-3F (2-53.1+)]. Recently isolated Dox-A2 mutations (2-53.9) are recessive, early larval lethals, which as heterozygotes reduce phenol oxidase activity. A homozygous mutant escaper had weak, completely unpigmented cuticle and unpigmented bristles. Enzyme assays show that Dox-A2 heterozygotes have diphenol oxidase activity reduced to 47-79% of wild type, whereas monophenol oxidase activity, at 94-106% of wild type, is normal. Elevated pool sizes of the diphenol oxidase substrates DOPA, dopamine, and N-acetyldopamine are observed in the mutant, confirming the enzyme assay results. Separation of the three phenol oxidase A component activities on polyacrylamide gels shows that Dox-A2 mutations reduce the activity of only the A2 component. Dox-A2 may identify a structural locus for the A2 component of the diphenol oxidase enzyme system. The Dox-A2 locus is one of 18 loci in the dopa decarboxylase, Df (2L)TW130 region of the second chromosome, at least 14 of which affect the formation, melanization or sclerotization of cuticle in some way. These loci form an apparent cluster of functionally related genes.

A diphenol oxidase gene is part of a cluster of genes involved in catecholamine metabolism and sclerotization in Drosophila. II. Molecular localization of the Dox-A2 coding region

Mutations at the Dox-A2 (2-53.9) locus alter the A2 component of diphenol oxidase, an enzyme having an important role in cuticle formation. This locus is in the dopa decarboxylase, Df(2L)TW130 region, which contains a cluster of at least 14 genes involved in catecholamine metabolism and the formation, sclerotization and melanization of cuticle in Drosophila. The region is subdivided by deficiencies, and localization of breakpoints in cloned DNA reveals a dense subcluster of six genes in the 23 kb proximal to Ddc. Five lethal loci distal to Ddc comprise a second such subcluster. The proximal breakpoints of deficiencies Df(2L)hk18 and Df(2L)OD15 define a 14.3- to 16.8-kb region containing Dox-A2 and l(2)37Bb, and those of Df(2L)OD15 and Df(2L)TW203 define a 9.3- to 12.1-kb region containing l(2)37Ba, l(2)37Bc and l(2)37Be. Southern blots show two of the Dox-A2 mutations are small deletions (0.1 and 1.1 kb). The Dox-A2 locus mRNA is 1.7 kb. cDNA clones indicate that the 3' end is centromere proximal and that the coding region contains at least one small intron. The Dox-A2 locus is within 3.4 to 4.4 kb of the Df(2L)OD15 breakpoint, placing four of the vital loci within a maximum of 15.5 kb. The location of Dox-A2 in a cluster of genes affecting cuticle formation is discussed.

Mutations of the Drosophila myosin heavy-chain gene: effects on transcription, myosin accumulation, and muscle function

Mutations of the myosin heavy-chain (MHC) gene of Drosophila melanogaster were identified among a group of dominant flightless and recessive lethal mutants (map position 2-52, 36A8-B1,2). One mutation is a 0.1-kilobase deletion in the 5' region of the MHC gene and reduces MHC protein in the leg and thoracic muscles of heterozygotes to levels found in 36AC haploids. Three mutations are insertions of 8-to 10-kilobase DNA elements within the MHC gene and produce truncated MHC transcripts. Heterozygotes of these insertional mutations possess levels of MHC intermediate between those of haploids and diploids. An additional mutation has no gross alteration of the MHC gene or its RNA transcripts. Although leg and larval muscles function normally in each mutant heterozygote, indirect flight muscles are defective and possess disorganized myofibrils. Homozygous mutants die during embryonic or larval development and display abnormal muscle function prior to death. These findings provide direct genetic evidence that the MHC gene at 36B (2L) is essential for both larval and adult muscle development and function. The results are consistent with the previous molecular evidence that Drosophila, unlike other organisms, has only a single muscle MHC gene per haploid genome. Quantitative expression of both copies of the MHC gene is required for function of indirect flight muscle, whereas expression of a single MHC gene is sufficient for function of larval muscles and adult tubular muscles.

Evidence for regulatory variants of the dopa decarboxylase and alpha-methyldopa hypersensitive loci in Drosophila

We have analyzed two variants of Drosophila melanogaster (RS and RE) which lead to the dual phenotype of elevated DDC activity and increased resistance to dietary alpha-methyldopa relative to Oregon-R controls. Both phenotypes show tight genetic linkage to the dopa decarboxylase, Ddc, and l(2)amd genes (i.e., less than 0.05 cM distant). We find that low (Oregon-R), medium (RS) and high (RE and Canton-S) levels of DDC activity seen at both pupariation and eclosion in these strains are completely accounted for by differences in accumulation of DDC protein as measured by immunoprecipitation. Genetic reconstruction experiments in which Ddc+ and amd+ gene doses are varied show that increasing DDC activity does not lead to a measurable increase in resistance to dietary alpha-methyldopa. This suggests that the increased resistance to dietary alpha-methyldopa is not the result of increased DDC activity but, rather, results from increased l(2)amd+ activity. Both cytogenetic and molecular analyses indicate that these overproduction variants are not the result of small duplications of the Ddc and amd genes, nor are they associated with small (greater than or equal to 100 bp) insertions or deletions. Measurements of DDC activity in wild-type strains of Drosophila reveal a unimodal distribution of activity levels with the Canton-S and RE strains at the high end of the scale, the Oregon-R control at the low end and RS near the modal value. We conclude that accumulated changes in a genetic element (or elements) in close proximity to the Ddc+ and amd+ genes lead to the coordinated changes in the expression of the Ddc and amd genes in these strains.

Molecular mapping of a gene cluster flanking the Drosophila Dopa decarboxylase gene

Nine lethal complementation groups flanking the Drosophila Dopa decarboxylase (Ddc) gene, have been localized within 100 kb of cloned chromosomal DNA. Six of these complementation groups are within 23 kb of DNA, and all ten complementation groups, including Ddc, lie within 78-82 kb of DNA. The potential significance of this unusually high gene density is discussed.

The genetics of dopa decarboxylase in Drosophila melanogaster. IV. The genetics and cytology of the 37B10-37D1 region

Of 204 mutations located in the 8-12 band Df(2L)130 region, 37B9-C1,2;37D1-2, 199 have been assigned to twelve lethal genes and one visible gene (hook). The 13 genes are not evenly distributed. Twelve, (possibly all thirteen) are in the seven band region 37B10-C4 giving a gene-to-band ratio of almost two. Only one gene, 1(2)37Cf, may be in the four band region 37C5-7, and none are localized in band 37D1. In situ hybridization places the dopa decarboxylase structural gene, Ddc, in or very close to band 37C1,2 (Hirsh and Davidson, 1981). The chi methyl dopa hypersensitive gene, 1(2) and, is 0.002 map units distal to Ddc. Df(2L)VA17, 37C1,2; 37F5-38A1 may actually break in the 37C1,2 singlet. It places six genes, hook, 1(2) and, and four lethal genes, in a maximum of five bands, 37B10, 11, 12, 13 and perhaps part of the 37C1,2 singlet and localizes six genes, Ddc plus five lethal genes, in a maximum of three bands; probably part of the 37C1,2 singlet plus bands, C3, and C4. Wild type activity of five of twelve lethal genes is necessary for female fertility. --Band 37C5 puffs at the time of pupariation; Puff Stages 8-10. Twelve of eighteen alleles of 1(2)37Cf have been examined as heterozygotes over CyO and none affect the appearance of a homozygous 37C5 puff. --Of the 204 mutations considered here only one Ddcpl, affects the function of more than one gene. It eliminates Ddc+ and 1(2)37Ca+ function and at 30 degrees C reduces 1(2)37Ce+ function. It is not a deficiency but could be a polar mutant.

The genetics of dopa decarboxylase in Drosophila melanogaster. II. Isolation and characterization of dopa-decarboxylase-deficient mutants and their relationship to the alpha-methyl-dopa-hypersensitive mutants

Of 84 lethals isolated over the dopa decarboxylase (DDC) deficiency Df(2L)50, 8 have been identified as DDC-deficient alleles on the basis of their effect on DDC activity when heterozygous over the Cgamma-O balancer chromosome with activities ranging from 28% to 53% of controls. Some of the Ddc-deficient alleles exhibit intracistronic complementation. Most of the complementing pairs of alleles are much reduced in viability, e.g. less than 5% of expected, and express a common syndrome of mutant phenes which can reasonably be inferred to derive from inadequately sclerotinized cuticle. Individuals heterozygous for the noncomplementing allele, Ddcn7, over the 12-band DDC deficiency, Df (2L)130, die at the end of embryogenesis as unhatched larvae with unpigmented mouth parts. The Ddc alleles and the l(2) amd alpha-methyl dopa (alphaMD) hypersensitive alleles are both located within the 11 band region 37B10-C7. The l(2) and locus is immediately to the right of hk(2-53.6). Ddc has been mapped within 0.004 Map Units to the right of l(2) and with a maximum estimated recombination frequency of 0.01%. None of the Ddc/CgammaOstrains are sensitive to the dietary administration of alpha-methyl dopa (alphaMD), and complementation occurs between the Ddc deficient alleles and the l(2) amd alleles both on the basis of viability and DDC activity. No effect on DDC by the amd alleles has been found to date. Even in the complementing heterozygote, amdH1/amdH89, the level of activity, thermostability, and in vitro alphaMD inhibition of DDC remains unaffected. Although no biochemical phene has yet been established for the alphaMD hypersensitive amd alleles, it seems likely that the two groups of mutants are functionally related.

The genetics of dopa decarboxylase in Drosophila melanogaster. I. Isolation and characterization of deficiencies that delete the dopa-decarboxylase-dosage-sensitive region and the alpha-methyl-dopa-hypersensitive locus

A detailed cytogenetic investigation of 16 overlapping deficiencies in the 36C-40A region on the left arm of the second chromosome (2L) in Drosophila melanogaster is reported. These deficiencies permit a localization of both the dopa-decarboxylase-dosage-sensitive region and the alpha-methyl-dopa-hypersensitive locus, l(2) amd, to the same region, 37B10-37C7.

Cold-sensitive mutants of Drosophila melanogaster defective in ribosome assembly

Thirteen X-linked, cold-sensitive lethal, female-sterile mutants of Drosophila melanogaster located at eight separate loci were screened for their ability to assemble ribosomes at the restrictive temperature of 17 degrees. Females were labelled with 3H-uridine for either 2 or 20 hours at 17 degrees. A mitochondria-free extract was prepared and analyzed by means of sucrose gradient centrifugation. Four of the mutants, l(1)TW-2cs, l(1)HM16cs, l(1)HM23cs, and l(1)HM20cs, had a lower ratio of cpm in the 40S subunit to cpm in the 60S subunit (40S:60S ratio) than wild type with a 2-hour label. The same was true of a 20-hour label of l(1)TW-2cs, l(1)HM16cs, and l(1)HM23cs, which are allelic, resulted in a 40S:60S ratio higher than wild type. Four other cs mutants were found to have less drastic effects on ribosome assembly. The ribosomal subunits of mutants l(1)HM16cs and l(1)HM20cs sediment at the same rate as their wild-type counterparts. The same is true for the RNA in their ribosomal particles. Sucrose gradient analysis of ribosomes from cold-sensitive lethal, female-sterile mutants appears to be an effective method for finding mutants that affect ribosome assembly.

A cold-sensitive zygotic lethal causing high frequencies of nondisjunction during meiosis I in Drosophila melanogaster females

The X-linked, cold-sensitive zygotic lethal, l(1)TW-6(cs), both in homozygous and heterozygous females, induces nondisjunction of all four chromosomes at Meiosis I at both 25 degrees and 17 degrees . Nondisjunction frequencies approaching 0.5 for the X and fourth chromosomes have been observed at 16 degrees -18 degrees . The disjunction of the X chromosomes in males is not affected. The mutant causes mitotic irregularities in zygotes at both 25 degrees and 17 degrees . Mortality of all zygotes produced by the crosses 6(cs)/6(cs)x6(cs)/B(s)Y and FM7/6(cs)x6(cs)/B(s)Y is respectively 86% and 67-74% at 25 degrees and 99.8-99.9% and 94% at 17 degrees . The mortality of 6(cs) hemizygotes derived from females carrying no doses of 6(cs) (C(1)DX,y f/yx6(cs)/B(s)Y) is 45-55% at 25 degrees and 98% at 17 degrees . The length of the temperature-sensitive period for 6(cs) homo- and hemizygotes is affected by the maternal dosage of 6(cs); the shortest TSP is for zero and the longest is for two maternal doses. Mortality takes place primarily during embryogenesis with some larval and little pupal mortality. Analysis of sectioned embryos indicates that the large array of different patterns of damage observed could have arisen from abnormal cleavage divisions and the incomplete population of the blastoderm with nuclei.

The developmental genetics of the temperature sensitive lethal allele of the suppressor of forked, 1(1)su(f)ts67g, in Drosophila melanogaster

A temperature-sensitive lethal allele of suppressor of forked, l(1)su(f)(ts67g) (ts67), has been discovered and characterized as follows: Flies which are hemizygous for ts67 live at 18 degrees and 25 degrees but die at 30 degrees primarily as larvae. The temperature-sensitive period for ts67 homozygotes or hemizygotes begins in second instar and ends at pupation. ts67 is lethal at 30 degrees when heterozygous with suppressor of forked (su(f)), a deficiency for suppressor of forked (su(f)(-)), and a non-conditional lethal allele of suppressor of forked (3DES). It is viable at 30 degrees when heterozygous with the wild-type allele of suppressor of forked. At 25 degrees but not at 18 degrees forked bristles are suppressed in flies of the following genotypes: f(s)ts67/Y, f(s)ts67/f(s)ts67, f(s)ts67/f(s)su(f), f(u)ts67/f(s)3DES, f(u)ts67/f(s)su(f)(-), f(u)ts67/f(s)su(f). There is some suppression of forked bristles at 25 degrees in the heterozygote, f(s)ts67/f(s)+(su(f)). The forked bristle phenotype is not suppressed at either temperature in flies of the genotypes f(u)ts67/Y, f(u)ts67/f(u)ts67/ (f(s) and f(u) indicating suppressible and unsuppressible alleles of forked). The temperature-sensitive period for suppression of forked bristles begins at pupation and extends through the period of bristle synthesis. The deficiency phenotype (bristles reduced in size or absent, wing wrinkled or blistered, eyes rough) typical of flies of the genotype f(s)su(f)/f(s)su(f)(-) at 18 degrees and 25 degrees , is exhibited by flies of the genotypes f(s)ts67/f(s)su(f)(-) at 25 degrees and f(u)ts67/f(s)su(f) at 29 degrees . An allele of lozenge (lz(1)) which can be suppressed by su(f) is suppressed at 25 degrees but not at 18 degrees in lz(1)ts67/Y males. ts67 homozygous females are fertile at 25 degrees but sterile at 30 degrees . The hypothesis is discussed that the su(f) locus codes for a ribosomal protein and that suppression and enhancement are affected by mutations at the locus by mutant ribosome-induced misreading. The possibility is presented that ts67 may be used to determine the translation time in development of any gene.