Deficiency of gustatory sensitivity to some deterrent compounds in "polyphagous" mutant strains of the silkworm, Bombyx mori

Sawa-J, CSJ02 and N601 x C601 are selected mutant strains of Bombyx mori, which grow on various artificial diets or temporarily ingest various plant leaves. To examine the mechanisms mediating diet breadth of caterpillars, gustatory spike responses of the silkworms, called 'polyphagous" strains, were compared with normal strains, N137 x C146 and C02. There were notable differences in their feeding habits and in their sensitivity to salicin in deterrent cells in the maxillary medial styloconic sensilla and the epipharyngeal sensilla. By contrast, the deterrent cells of all strains responded similarly to strychnine nitrate in a dose-dependent manner. In additional comparisons of Sawa-J and N137 x C146, Sawa-J maxillary deterrent cells were significantly less sensitive to phloridzin, amygdalin and arbutin, but responded to some alkaloids and 20-hydroxyecdysone with similar or even higher firing rate. These results suggest that the deficiency of the sensitivity to some deterrent compounds on the deterrent cell of the polyphagous strains may be caused by mutant genes and affects the diet breadth of caterpillars.     

Genetic mapping of a food preference gene in the silkworm, Bombyx mori, using restriction fragment length polymorphisms (RFLPs)

The domesticated silkworm, Bombyx mori, has strict food preferences and grows by feeding on mulberry leaves. However, "Sawa-J", an abnormal feeding habit strain selected from the genetic stock, feeds on an artificial diet without mulberry leaf powder. In this study, the food preference gene in Sawa-J was genetically identified using restriction fragment length polymorphisms (RFLPs) of a cDNA clone on each linkage group. Taking advantage of a lack of genetic recombination in females, reciprocal backcrossed F1 (BC1) progenies were independently prepared using a non-feeding strain, C108, as a mating partner of Sawa-J. Our results of linkage analysis and mapping proved that the feeding behavior is primarily controlled by a major recessive gene mapped at 20.2 cM on RFLP linkage group 9 (RFLG9), and clone e73 at a distance of 4.2 cM was found as the first linked molecular marker.     

Experience-based behavioral and chemosensory changes in the generalist insect herbivore Helicoverpa armigera exposed to two deterrent plant chemicals

Behavioral and electrophysiological responses of larvae of the polyphagous moth species Helicoverpa armigera to two plant-derived allelochemicals were studied, both in larvae that had been reared on a diet devoid of these compounds and in larvae previously exposed to these compounds. In dual-choice cotton leaf disk and pepper fruit disk arena assays, caterpillars reared on a normal artificial diet were strongly deterred by strychnine and strophanthin-K. However, caterpillars reared on an artificial diet containing strychnine were insensitive to strychnine and strophanthin-K. Similarly, caterpillars reared on an artificial diet containing strophanthin-K were also desensitized to both deterrent chemicals. Electrophysiological tests revealed that the deterrent-sensitive neurons in taste sensilla on the maxillae of caterpillars reared on each deterrent-containing diet displayed reduced sensitivity to the two chemicals compared with the caterpillars reared on normal diets. We conclude that the experience-dependent behavioral plasticity was partly based on the reduced sensitivity of taste receptor neurons and that the desensitization of taste receptor neurons contributed to the cross-habituation to the two chemicals.     

Taste cell responses in the polyphagous arctiid, Grammia geneura: towards a general pattern for caterpillars

The caterpillars of Grammia geneura are polyphagous as individuals. Electrophysiological responses of its medial and lateral galeal styloconic sensilla to 21 amino acids, 6 carbohydrates, 10 chemically diverse plant secondary compounds and two inorganic salts were examined. In the medial sensillum, a single cell responded to 8 amino acids, 3 carbohydrates, and the iridoid, catalpol, which is present in a favored hostplant. In the lateral sensillum, one cell responded to amino acids and another to fructose. Two cells in each sensillum responded to secondary compounds and it is suggested that the same cells are stimulated by inorganic salts. There was no evidence of a separate salt-sensitive cell. Phenylalanine stimulated a deterrent cell in the medial sensillum and was behaviorally deterrent. Some essential amino acids did not stimulate any cells and it is suggested that a small number of amino acids (sometimes non-essential) may serve as indicators of nutrient quality. Sugars probably serve as the primary phagostimulants because they are in relatively high concentrations in plants. It is proposed that taste receptor cells should be categorized primarily by their behavioral effects as phagostimulatory or deterrent, rather than their specific ranges of responsiveness. This would emphasize the basic similarities across taxa.     

Determining the order of genes,centromeres, and rearrangement breakpoints inNeurospora by tests of duplication coverage

Nontandem segmental duplications provide a useful alternative to conventional recombination mapping for determining gene order in a haploid organism such asNeurospora. When an insertional or terminal rearrangement is crossed by Normal sequence, a class of progeny is produced that have a precisely delimited chromosome segment duplicated. In such Duplication progeny, a recessive gene in the Normal-sequence donor chromosome may or may not be masked (“covered”) by its dominant wild-type allele in the translocation-sequence recipient chromosome. Coverage depends upon whether the gene in question is left or right of the rearrangement breakpoint. The recessive gene will be heterozygous and covered (not expressed) if its locus is within the duplicated segment, but it will be haploid and expressed if the locus is outside the segment. Not only genes but also centromeres can be mapped by means of duplications, because genes included in. the same viable duplication must reside in the same chromosome arm. - Numerous sequences in the current genetic maps ofN. crassa have been determined using duplications. Gene order in the albino region and in the centromere region of linkage group I provide examples. Over 50 insertional or terminal rearrangements are available from which nontandem duplications of defined content can be obtained at will; collectively these cover about 75% of the genome. - Intercrosses between partially overlapping chromosome rearrangements also produce Duplication progeny containing two copies of regions between the breakpoints. The 180 mapped reciprocal translocations and inversions include numerous overlapping combinations that can be used for duplication mapping.     

小麦农家品种大籽糙抗条锈性的遗传分析

以抗条锈病的农家品种大籽糙作父本、感病品种铭贤169作母本杂交获得F1代杂交种,F1代植株自交获得F2代种子,F1代植株与铭贤169回交获得 BC1代种子。在人工控制条件下,用我国小麦条锈菌优势小种条中28号和条中32号,分别对F1、F2、BC1代及其亲本的幼苗进行人工接种,研究了它们的抗性表现和杂交后代中抗条锈性的分离情况。结果表明,大籽糙对条中32号小种的抗性由一对隐性基因控制;对条中28号小种的抗性由一对显性基因和一对隐性基因的互补作用控制。 Abstract:Dazicao,a native wheat variety with stripe rust resistance from Henan,China,was crossed with susceptible cultivar Mingxian 169 as the female parent.The F1 progeny was selfed to produce F2 progeny and backcrossed with Mingxian 169 to produce BC1 progeny.In air-conditioned greenhouse,seedlings of the F1,F2,BC1 progenies and their parents were inoculated with the prevalent races CY28 and CY32 of Puccinia striiformis respectively.The phenotypes of the F1,F2 and BC1 plants were analyzed for resistance to the two races.The results indicated that the resistance in the Dazicao to race CY32 was controlled by one recessive gene,and the resistance to race CY28 by complementary action of one dominant gene and one recessive gene.     

Dissection of a major QTL for photoperiod sensitivity in rice: its association with a gene expressed in an age-dependent manner

 A proposed major quantitative trait locus (QTL) for photoperiod sensitivity on chromosome 6 in rice was examined by introducing a chromosomal segment from a sensitive line into an insensitive one. The crossing experiments showed that a range of variation in heading date occurred in the later generations and that the region might contain at least a major gene and two additional recessive genes controlling photoperiod sensitivity. Gene mapping experiments showed that the major gene was Se-1 and that a recessive gene (tentatively named se-pat) was loosely linked to it. The responses to photoperiods were examined among the different genotypes under natural and controlled conditions. The two genes acted additively on the degree of photoperiod sensitivity. However, se-pat plants showed a response to photoperiods that differed from that of the other sensitive lines; a short-day treatment at the seedling stage delayed heading in the former plants, suggesting that the manner of its expression was age-dependent. A recessive gene similar to se-pat seemed to be widely distributed in wild and cultivated rice, suggesting that the gene complex in the region plays a significant role in response to photoperiod. Received: 8 October 1997 / Accepted: 1 April 1998     

A Fourth Escherichia Coli Gene System with the Potential to Evolve β-Glucoside Utilization

Escherichia coli K12 is being used to study the potential for adaptive evolution that is present in the genome of a single organism. Wild-type E. coli K12 do not utilize any of the beta-glucoside sugars arbutin, salicin or cellobiose. It has been shown that mutations at three cryptic loci allow utilization of these sugars. Mutations in the bgl operon allow inducible growth on arbutin and salicin while cel mutations allow constitutive utilization of cellobiose as well as arbutin and salicin. Mutations in a third cryptic locus, arbT, allow the transport of arbutin. A salicin+ arbutin+ cellobiose+ mutant has been isolated from a strain which is deleted for the both the bgl and cel operons. Because the mutant utilized salicin and cellobiose as well as arbutin, it is unlikely it is the result of a mutation in arbT. A second step mutant exhibited enhanced growth on salicin and a third step mutant showed better growth on cellobiose. A fourfold level of induction in response to arbutin and a twofold level of induction in response to salicin was observed when these mutants were assayed on the artificial substrate p-nitrophenyl-beta-D-glucoside. Although growth on cellobiose minimal medium can be detected after prolonged periods of time, these strains are severely inhibited by cellobiose in liquid medium. This system has been cloned and does not hybridize to either bgl or cel specific probes. We have designated this gene system the sac locus. The sac locus is a fourth set of genes with the potential for evolving to provide beta-glucoside utilization.     

Biochemical Genetics of the Cryptic Gene System for Cellobiose Utilization in Escherichia coli K12

The cellobiose catabolic system of Escherichia coli K12 is being used to study the role of cryptic genes in microbial evolution. Wild-type E. coli K12 do not utilize the beta-glucoside sugars, arbutin, salicin and cellobiose. A Cel+ (cellobiose utilizing) mutant which grows on cellobiose, arbutin, and salicin was isolated previously from wild-type E. coli K12. Biochemical assays indicate that a cel structural gene (celT) specifies a single transport protein that is a beta-glucoside specific enzyme of the phosphoenolpyruvate-dependent phosphotransferase system. The transport protein phosphorylates beta-glucosides at the expense of phosphoenolpyruvate. A single phosphoglucosidase, specified by celH, hydrolyzes phosphorylated cellobiose, arbutin, and salicin. The genes of the cel system are expressed constitutively in the Cel+ mutant, whereas they are not expressed at a detectable level in the wild-type strain. The transport and hydrolase genes are simultaneously silenced or simultaneously expressed and thus constitute an operon. Cel+ strains which fail to utilize one or more beta-glucosides express the transport system at a lower level than do Cel+ strains which grow on all three beta-glucosides. Other strains inducibly express a gene which specifies transport of arbutin but not the other beta-glucosides. The arbutin transport gene, arbT, maps outside of the cel locus.     

Inheritance of trunk striping in the Sumatran tiger barb, Barbus tetrazona

The Sumatran tiger barb, Barbus tetrazona, exhibits three truck (pelvic) striping phenotypes: complete, incomplete, and half banded. Segregation patterns observed in the progeny from 12 different matings indicate that the inheritance of these phenotypes is controlled by two autosomal gene loci acting additively, with complete dominance at each locus.     

Genetics of Biomphalaria glabrata: Linkage analysis of genes for pigmentation,enzymes, and resistance to Schistosoma mansoni

The snail, Biomphalaria glabrata, is a major intermediate host of the human blood fluke, Schistosoma mansoni, in the Americas. The inheritance and linkage relationships of a gene enabling adult snails to resist infection by a Puerto Rican strain of the parasite were analyzed using two laboratory stocks that differed in susceptibility, pigmentation, and five electrophoretically detectable enzyme markers. Segregation ratios in second-generation intraspecific hybrids between susceptible (M-stock) and resistant (10-R2-stock) snails indicate that the susceptibility gene is not linked to the enzyme (ACON-1, ACP, EST-2, PEP-2, PGD) or pigmentation loci studied. These seven loci assort independently of one another. Observed rates of infection among F1 and F2 progeny are consistent with Richards' finding that adult susceptibility to the PR-1 strain of S. mansoni is controlled by a single locus with resistance dominant. No association between allozymes of acid phosphatase and snail susceptibility to PR-1 was seen in the snail-parasite combinations studied.     

Pleiotropic effect of a locus on chromosome 4 influencing alcohol drinking and emotional reactivity in rats

A QTL search in a segregating F2 intercross between HEP (High-Ethanol Preferring line) and wistar-kyoto (WKY, a low-alcohol consuming strain) rats identified a locus on chromosome 4 linked to the consumption of a 5% alcohol solution offered as a free choice with water (Terenina-Rigaldie et al. submitted). In order to confirm and analyse the influence of this locus, F2 rats were selected according to their genotype at the markers flanking the QTL and bred in order to obtain two groups of rats homozygous HEP/HEP ('HIGH' line) or WKY/WKY ('LOW' line) at the QTL, the rest of the genome being randomly inherited from one or the other founder strain. These two groups of animals displayed large differences in emotional reactivity (open field, elevated-plus maze), sensitivity to taste reinforcers (saccharin, quinine) and alcohol consumption (either forced or as a free choice with water). These results confirm the influence of this locus on alcohol intake and emotional reactivity traits, and suggest a pleiotropic effect of the gene(s) involved. Current research aims at the identification of this (these) gene(s).     

Linkage mapping of the locus responsible for male pseudohermaphroditism (mp) on rat chromosome 7.

TF is a mutant rat strain showing male pseudohermaphroditism controlled by an autosomal single recessive gene (mp). The affected rats show lack of Leydig cells and androgen deficiency. In this study, we performed linkage analysis using F(2) progeny of crosses between TF and BN strains to determine the chromosomal localization of the mp locus. The mp locus was mapped in a 4 cM region of the distal region of rat chromosome 7 between D7Rat3 and D7Rat115 or D7Rat94. Comparison of the linkage map with corresponding regions of the published rat genome sequence revealed several candidate genes for the mp mutation, including the Dhh, Tegt, Gdp3, and Amhr2 genes.     

Genetic mapping a meiotic driver that causes sex ratio distortion in the mosquito Aedes aegypti

An endogenous meiotic driver in the dengue and yellow fever vector mosquito Aedes aegypti can cause highly male-biased sex ratio distortion in crosses from suitable genetic backgrounds. We previously selected a strain that carries a strong meiotic drive gene (D) linked with the male-determining allele (M) on chromosome 1 in A. aegypti. Here, we performed segregation analysis of the M(D) locus among backcross (BC(1)) progeny from a driver male and drive-sensitive females. Assessment of sex ratios among BC(2) progeny showed ～5.2% recombination between the M(D) locus and the sex determination locus. Multipoint linkage mapping across this region revealed consistent marker orders and recombination frequencies with the existing reference linkage map and placed the M(D) locus within a 6.5-cm interval defined by the LF159 locus and microsatellite marker 446GAA, which should facilitate future positional cloning efforts.     

Salicin from host plant as precursor of salicylaldehyde in defensive secretion of Chrysomeline larvae

ABSTRACT. Phratora vitellinae L. and Chrysomela tremulae F. (Chrysomelinae, Coleoptera) feed on Salix or Populus spp. (Salicaceae). Their larvae, as well as the larvae of other chrysomelines feeding on Salicaceae, secrete salicylaldehyde. In this study, we demonstrate that salicylaldehyde is derived from salicin, a phenylglucoside present in the leaves of the host plant. The concentration of salicylaldehyde in the secretion is positively correlated with the amount of salicin in the food of the larvae. The transformation of salicin into salicylaldehyde occurs in the defence glands since the β-glucosidase activity is 4 times higher in their glands than in the gut. The larvae recover most of the glucose that results from the hydrolysis of salicin. For generalist predators, such as ants, salicylaldehyde is a more potent deterrent than saligenin or salicin.     

Mutations in the Saccharomyces Cerevisiae Type 2a Protein Phosphatase Catalytic Subunit Reveal Roles in Cell Wall Integrity, Actin Cytoskeleton Organization and Mitosis

Temperature-sensitive mutations were generated in the Saccharomyces cerevisiae PPH22 gene that, together with its homologue PPH21, encode the catalytic subunit of type 2A protein phosphatase (PP2A). At the restrictive temperature (37°), cells dependent solely on pph22(ts) alleles for PP2A function displayed a rapid arrest of proliferation. Ts(-) pph22 mutant cells underwent lysis at 37°, showing an accompanying viability loss that was suppressed by inclusion of 1 M sorbitol in the growth medium. Ts(-) pph22 mutant cells also displayed defects in bud morphogenesis and polarization of the cortical actin cytoskeleton at 37°. PP2A is therefore required for maintenance of cell integrity and polarized growth. On transfer from 24° to 37°, Ts(-) pph22 mutant cells accumulated a 2N DNA content indicating a cell cycle block before completion of mitosis. However, during prolonged incubation at 37°, many Ts(-) pph22 mutant cells progressed through an aberrant nuclear division and accumulated multiple nuclei. Ts(-) pph22 mutant cells also accumulated aberrant microtubule structures at 37°, while under semi-permissive conditions they were sensitive to the microtubule-destabilizing agent benomyl, suggesting that PP2A is required for normal microtubule function. Remarkably, the multiple defects of Ts(-) pph22 mutant cells were suppressed by a viable allele (SSD1-v1) of the polymorphic SSD1 gene.     

The isolation of abscisic acid (ABA) deficient mutants by selection of induced revertants in non-germinating gibberellin sensitive lines of Arabidopsis thaliana (L.) heynh.

Summary By selecting for germinating seeds in the progeny of mutagen-treated non-germinating gibberellin responsive dwarf mutants of the ga–1 locus in Arabidopsis thaliana, germinating lines (revertants) could be isolated. About half of the revertants were homozygous recessive for a gene (aba), which probably regulates the presence of abscisic acid (ABA). Arguments for the function of this gene were obtained from lines homozygous recessive for this locus only, obtained by selection from the F₂ progeny of revertant X wild-type crosses. These lines are characterized by a reduced seed dormancy, symptoms of withering, increased transpiration and a lowered ABA content in developing and ripe seeds and leaves.Abbreviations ABA Abscisic acid - GA₄₊₇ Mixture of gibberellin A₄ and A₇ - EMS Ethylmethanesulfonate - NG Non-germinating - G Germinating     

Chemical defence in chrysomelid eggs and neonate larvae

ABSTRACT. Eggs and neonate larvae of chrysomelid beetles (sub-tribes Chrysomelina and Phyllodectina) were investigated for the presence of defensive substances.
The two isoxazolinone glucosides (compounds 1 and 2), characteristic of the adult defence secretion, were detected in the eggs of all studied species. Compound 2, containing a nitropropionate, is always present in concentrations (above 10^-2 M), which are highly deterrent to the ant Myrmica rubra. This compound is not at all or only slightly toxic to ants at 10^-2 M. Compound 1, devoid of nitropropionate, is a minor constituent, and is neither deterrent nor toxic to ants.
The five Chrysomela species studied and Phratora vitellinae also sequester salicin in their eggs in amounts highly deterrent and toxic to ants. A single Chrysomela egg often contains enough salicin to kill an ant. While the isoxazolinones are discarded with the egg shells, salicin is used by neonate larvae as a precursor for the production of salicylaldehyde in the thoracic defence glands, already functional at hatching. No salicin could be detected in the eggs of those species whose larvae produce cyclopentanoid monoterpenes, even if they feed on Salicaceae. No larva of any species seems to be able to produce detectable amounts of monoterpenes at birth. A very early defence, possible only in those species using salicin as the precursor for their defensive secretion, could be highly advantageous in protecting the clustered larvae during the long process of hatching and in avoiding cannibalism between siblings.
Only trace amounts of oleic acid were found in the eggs of Gastrophysa viridula , in contrast to previous reports on its presence in large quantities in the American G. cyanea.     

Clonidine effects on protein and carbohydrate electrophysiological responses of labellar and tarsal sensilla in Phormia regina

The electrophysiological response of labellar and tarsal chemosensilla in the blowfly Phormia regina was studied in response to a complex stimulus naturally encountered by flies such as sheep faeces, and to beef liver, a proteinaceous feeding source. Responses were investigated both before or after injection of clonidine, an octopamine agonist previously shown to enhance sucrose ingestion, while decreasing that of proteins. As assessed by single sensillum recordings, the four different chemosensory - "salt", "sugar", "deterrent" and "water" - cells were all activated by both stimuli, regardless of sex and sensillum type, the "sugar" one being in all cases the most sensitive to beef liver before clonidine injection. Clonidine treatment affected neither labellar nor tarsal sensitivity to sucrose. Conversely, clonidine-injected flies showed a significant increase in the activity of the "deterrent" cell to beef liver, thus accounting for a decrease in protein ingestion. This study for the first time provides evidence of a key role of a clonidine-sensitive peripheral taste sensitivity in down-regulation of protein ingestion in blowflies. Correlation between peripheral sensitivity and behavioural output is discussed.     

Epigenetic control of chromosome breakage at the 5' end of Paramecium tetraurelia gene A

Macronuclei and micronuclei of ciliates have related genomes, with macronuclei developing from zygotic micronuclei through programmed DNA rearrangements. While Paramecium tetraurelia wild-type strain 51 and mutant strain d48 have the same micronuclear genome, qualitative differences between their macronuclear genomes have been described, demonstrating that programmed DNA rearrangements could be epigenetically controlled in ciliates. Macronuclear chromosomes end downstream of gene A (A51 Mac ends) and at the 5' end of gene A (Ad48 Mac ends) in strains 51 and d48, respectively. To gain further insight into the process of chromosome end formation, we performed an extensive analysis of locus A rearrangement in strains d48 and 51, in strain d12, which harbors a gene A deletion, and in interstrain cross progeny. We show that (i) allele Ad12 harbors a deletion of >16 kb, (ii) A51 Mac ends distribute over four rather than three DNA regions, (iii) strains d48 and 51 display only quantitative differences (rare Ad48 and A51 Mac ends do form in strains 51 and d48, respectively), (iv) the level of A51 Mac ends is severalfold enhanced in d12- and d48-derived progeny, and (v) this level inversely correlates with the level of Ad48 Mac ends in the d48 parent. Together, these data lead to a model in which the formation of Ad48 Mac ends is epigenetically controlled by a d48 factor(s). We propose that the d48 factor(s) may be derived from RNA molecules transcribed from the Ad48 Mac ends and encompassing the truncated A gene and telomeric repeats.