Tests of two models for the transmission of the Mu mutator in maize

Summary The mutator system Mu does not follow a typical Mendelian mode of transmission. In outcrosses in which 50 per cent mutator plants are expected, about 90 per cent are observed. Two possible models of transmission are tested. One assumes that Mu has segregation distortion activity such as has been described for the SD locus in Drosophila. The second model assumes an extra-chromosomal factor that is transmitted through the cytoplasm. No evidence of SD activity was found. Mutation frequencies in lines in which Mu was transmitted through the female were not greater than the frequencies observed when Mu was transmitted through the male; as might be expected on some models of cytoplasmic transmission. Thus, cytoplasmic transmission was not established. Other possible models of extrachromosomal inheritance that might not be detected by reciprocal crosses are discussed.     

The Fcu controlling-element system in maize

Summary The relationship between the Fcu controlling-element system and the spotted-dilute R system was investigated. The Fcu controlling-element system consists of the receptor element allele r-cu and the regulatory element Fcu. The equivalent components of the spotted-dilute R system are respectively R-r#2 (or R-r#2 Dil) and Spf. The R-r#2 allele of the latter system was shown to be responsive (mutable) to Fcu, provided that it has had an uninterrupted association with Dil or Dpf as evidenced by the color variegation of the aleurone tissue. The reverse test, in which the r-cu allele of the Fcu controlling element system was tested for its response to Spf, proved negative. This was surprising in view of the relationship and specificity between systems. The possibility was considered that maize controlling elements may have different sizes as is known for bacterial insertion sequences. —The variable dilute pigmenting capacity of the r-cu allele also was studied. A given level of r-cu-induced pigmentation, despite the wide range in pigmentation expression, was found to be generally non-heritable, as based on a test of correspondence between parent and progeny.Journal Paper No. J-9204 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 1884Now with Funk's Seeds, Casalmorano (Cremona), Italy     

Oenothera chloroplast DNA polymorphisms associated with plastome mutator activity

Summary Oenothera plants homozygous for a recessive allele at the plastome mutator (pm) locus show non-Mendelian mutation frequencies that are 1000-fold higher than spontaneous levels. Chloroplast DNA (cpDNA) was isolated from nine mutants and two green isolates of the plastome mutator line. cpDNA restriction patterns were compared to cpDNA from a representative of the progenitor Johansen strain, and cpDNAs from all eleven plastome mutator lines show changes of fragment mobility due to deletion events at five discrete regions of the plastome. Most of the mutants have cpDNA restriction patterns identical to that of one of the green isolates from the plastome mutator line, and therefore, most of the differences in fragment length are probably not responsible for the mutant phenotypes. In contrast to the plastome mutator line, cpDNA from several populations of a closely related wild-type Oenothera species have few restriction fragment length polymorphisms. This suggests that both mutation frequencies and site-specific cpDNA deletions are elevated in the plastome mutator line, and implicates a defect in the cpDNA repair or replication machinery.     

Tests of two models for the transmission of the Mu mutator in maize

Molecular Genetics and Genomics - The mutator system Mu does not follow a typical Mendelian mode of transmission. In outcrosses in which 50 per cent mutator plants are expected, about 90 per cent...     

Regulation of Mu element copy number in maize lines with an active or inactive Mutator transposable element system

Summary In the progeny of an active Mutator plant, the number of Mu elements increases on self-pollination and maintains the average parental Mu content on outcrossing to a non-Mutator line; both patterns of transmission require an increase in the absolute number of Mu elements from one generation to the next. The same average copy number of Mu elements is transmitted through the male and female, but there is wide variation in the absolute copy number among the progeny. In inactive Mutator plants —defined both by the loss of somatic instability at a reporter gene (bronze2-mu1) and by modification of the HinfI sites in the terminal inverted repeat sequences of Mu elements —the absolute copy number of Mu elements is fixed in the parent. Thus, in outcrosses Mu element number is halved, and on self-pollination Mu copy number is constant. Reactivation of somatic mutability at cryptic bz2-mu1 alleles in inactive individuals by crossing to an active line seems not to involve an increase in Mu element copy number transmitted by the inactive individual. These and other results suggest that increases in Mu copy number occur late in plant development or in the gametophyte rather than after fertilization.     

Locomotor activity of Sitophilus zeamais and Sitotroga cerealella on maize

Some aspects of the locomotor activity of two pests of stored maize, Sitophilus zeamais Mots. and Sitotroga cerealella (Oliv.) were studied in the laboratory using a light dependent resistor actograph. Activity of S. zeamais adults increased weekly for 4 weeks and virgin males were more active than virgin females of the same age. When the sexes were mixed activity was intermediate between that of the separate sexes for about 3 weeks. Observations made on adults of S. cereablella for 4 days showed a daily increase in moth activity. When S. zeamais and S. cerealella were observed together, activity increased initially to about twice the mean activity of the species separately. Over 24 hr observation periods, no overt rhythms of activity were recorded for either species but S. zeamais was slightly more active between 11 and 19 hr GMT while in S. cerealella periods of low and high activity appeared to alternate nearly every 4–7 hours.

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Résumé Quelques aspects de l'activité locomotrice de deux ennemis du mais stocke Sitophilus zeamais Mots. et Sitotroga cerealella Oliv. ont été étudiés au laboratoire avec un actographe à résistor fonctionnant à la lumière.L'activité des adultes de S. zeamais augmente chaque semaine pendant 4 semaines, et les mâles vierges sont plus actifs que les femelles vierges du même âge. Quand les sexes sont mélangés l'activité est intermédiaire à celle des sexes séparés pour 3 semaines.Les observations sur 4 jours des adultes de S. cerealella montre une augmentation quotidienne de l'activité.Quand S. zeamais et S. cerealella sont observés ensemble, l'activité commence par doubler par rapport à celle des espèces séparées. Avec des observations par périodes de 24 heures, aucun rythme clar d'activité n'a été enregistré pour ces espèces, mais S. zeamais est légèrement plus actif entre 11 h et 19 h GMT, tandis que les périodes de faible et forte activités de S. cerealella apparaissent alternativement toutes les 4 à 7 heures.

     

Tcl transposition and mutator activity in a Bristol strain of Caenorhabditis elegans

Summary In most strains of Caenorhabditis elegans with a low copy number of Tc1 transposable elements, germline transposition is rare or undetectable. We have observed low-level Tel transposition in the genome of the C. elegans var. Bristol strain KR579 (unc-13[e51]) resulting in an increase in Tc1 copy number and subsequent mutator activity. Examination of genomic blots from KR579 and KR579derived strains revealed that more Tc1-hybridizing bands were present than in other Bristol strains. A novel Tc1-hybridizing fragment was cloned from a KR579-derived strain. Unique sequence DNA flanking the Tc1 element identified a 1.6 kb restriction fragment length difference between the KR579 and N2 strains consistent with a Tc1 insertion at a new genomic site. The site of insertion of this Tel was sequenced and is similar to the published Tel insertion site consensus sequence. Several isolates of KR579 were established and maintained on plates for a period of 3 years in order to determine if Tc1 copy number would continue to increase. In one isolate, KR1787, a further increase in Tc1 copy number was observed. Examination of the KR1787 strain has shown that it also exhibits mutator activity as assayed by the spontaneous mutation frequency at the unc-22 (twitcher) locus. The KR579 strain differs from most low copy number strains in that it exhibits low-level transposition which has developed into mutator activity.     

TheisfA mutation inhibits mutator activity and processing of UmuD protein inEscherichia coli recA730 strains

Further studies on theisfA mutation responsible for anti-SOS and antimutagenic activities inEscherichia coli are described. We have previously shown that theisfA mutation inhibits mutagenesis and other SOS-dependent phenomena, possibly by interfering with RecA coprotease activity. TheisfA mutation has now been demonstrated also to suppress mutator activity inE. coli recA730 andrecA730 lexA51(Def) strains that constitutively express RecA coprotease activity. We further show that the antimutator activity of theisfA mutation is related to inhibition of RecA coprotease-dependent processing of UmuD. Expression of UmuD' from plasmid pGW2122 efficiently restores UV-induced mutagenesis in therecA730 isfA strain and partially restores its mutator activity. On the other hand, overproduction of UmuD'C proteins from pGW2123 plasmid markedly enhances UV sensitivity with no restoration of mutability.     

Genetic studies on the loss of mu mutator activity in maize

Mutator activity of the Mu mutator system of maize can be lost by either outcrossing or inbreeding Mu stocks. The nature of these two kinds of Mu-loss phenomena was analyzed by testing the results of crossing Mu-loss stocks by active Mu lines. Outcross- Mu-loss stocks are capable of supporting Mu activity if crossed by an active mutator line. Inbred-Mu-loss stocks, however, inactivate the active Mu system contributed by a Mu line. Also, inbred- Mu-loss lines do not regain Mu activity after at least three generations of outcrossing to non-Mu stocks. These results suggest that, once the Mu system is inactivated by inbreeding, it remains inactivated for at least three generations of outcrossing. Further, once the system responsible for inactivation is established, it will, in turn, inactivate an active Mu system contributed by crossing with Mu plants. The outcross-Mu-loss does not seem to involve such an inactivation system. These results are interpreted in the light of recent evidence that Mu inactivation results from the modification of Mu 1 transposable elements involved in the Mu phenotype.     

Interaction of an Escherichia coli mutator gene with a deoxyribonucleotide effector

Summary Strains of Escherichia coli carrying mutD5 display very high mutation rates (about 10⁴-fold above wild-type) when grown in rich medium, but relatively low mutation rates (about 10- to 50-fold above wild-type) in minimal medium. Thymidine, deoxycytidine, and deoxyuridine are all capable of stimulating mutation when added to minimal medium. Studies with mutants blocked in various steps of thymidine metabolism implicate a phosphorylated thymidine effector which mediates the mutagenic action of the added deoxyribonucleotides. In addition, an unidentified compound or compounds other than thymidine present in rich medium (L-broth) can also increase the mutation rate.     

Genetic evidence of a relationship between two maize transposable element systems: Cy and Mutator

Summary The Cy transposable element system is composed of two genetically defined elements: an rcy receptor element inserted at the Bronze-1 locus; and an independently segregating regulatory element, Cy. The Cy system is not functionally homologous to any of the non-Mutator transposable element systems. Evidence is presented that supports a relationship between the Cy system and the family of Mu1-homologous transposable elements that are responsible for the Mutator phenomenon. Although related, Cy elements and the Mu1-homologous elements are not identical; Cy is inherited in a near-Mendelian fashion, in contrast to the non-Mendelian inheritance of the Mu1-homologous elements.     

Spm and I element changes with the a-m2 8004 allele in maize

Summary Among the mobile element systems in maize, the En (Spm) system (En — the regulatory element and I the receptive element — a nonfunctional En) has several interesting aspects of control of gene expression (En and Spm are homologous in structure and activity). One of the alleles arising from the Spm group included the a-m2 8004 allele that has a low spotting pattern and unique ringed areas. The interest in this allele is that Spm or En will induce it to co-express the A phenotype and mutability. Several exceptions of the allele were analyzed. Two are Spm changes and two are I changes. The analysis shows that the heritable changes include I changes that are co-expressed in various grades of color and different degrees of mutability. All these changes occur with I at the locus. The Spm changes also include changes in mutability patterns and a mottling pattern.Journal Paper No., J-11792 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project No. 2381     

Infection of maize leaves with Ustilago maydis prevents establishment of C4 photosynthesis

The Basidiomycete fungus Ustilago maydis is the common agent of corn smut and is capable of inducing gall growth on infected tissue of the C₄ plant maize (Zea mays). While U. maydis is very well characterized on the genetic level, the physiological changes in the host plant in response to U. maydis infection have not been studied in detail, yet.Therefore, we examined the influence of U. maydis infection on photosynthetic performance and carbon metabolism in maize leaf galls.At all stages of development, U. maydis-induced leaf galls exhibited carbon dioxide response curves, CO₂ compensation points and enzymatic activities that are characteristic of C₃ photosynthesis, demonstrating that the establishment of C₄ metabolism is prevented in infected tissue. Hexose contents and hexose/sucrose ratio of leaf galls remained high at 6 days post infection, while a shift in free sugar metabolism was observed in the uninfected controls at that time point. Concomitantly, transitory starch production and sucrose accumulation during the light period remained low in leaf galls. Given that U. maydis is infectious on young developing tissue, the observed changes in carbohydrate metabolism suggest that the pathogen manipulates the developing leaf tissue to arrest sink-to-source transition in favor of maintaining sink metabolism in the host cells.Furthermore, evidence is presented that carbohydrate supply during the biotrophic phase of the pathogen is assured by a fungal invertase.     

Synthesis of nitrodiazirinyl derivatives of neurotoxin II fromNaja naja oxiana and their interaction with theTorpedo californica nicotinic acetylcholine receptor

Five singly modified nitrodiazirine derivatives of neurotoxin II (NT-II) fromNaja naja oxiana were obtained after NT-II reaction with N-hydroxysuccinimide ester of {2-nitro-4 [3-(trifluoromethyl)-3H-diazirin-3yl]phenoxy}acetic acid followed by Chromatographic separation of the products. To localize the label positions, each derivative was first UV-irradiated and then subjected to reduction, carboxymethylation, and trypsinolysis. Tryptic digests were separated by reversed phase-HPLC, the labeled peptides being identified by mass spectrometry. The derivatives containing the photolabel at the position Lys 25, Lys 26, Lys 44, or Lys 46 were [¹²⁵I]iodinated by the chloramine T procedure. Each iodinated derivative was found to form photoinduced cross-links with the membrane bound nicotinic acetylcholine receptor (AChR) fromTorpedo californica. The pattern of labeling the receptor's, , , or subunits was dependent on the photolabel position in the NT-II molecule and differed from that obtained earlier with an analogous series ofp-azidobenzoyl derivatives of NT-II. The results obtained indicate that (i) different sides of the neurotoxin molecule are involved in the AChR binding, and (ii) fragments of the different AChR subunits are located close together at the neurotoxin-binding sites.Abbreviations AChR Acetylcholine receptor - NDPA [2-nitro-4-[3-(trifluoromethyl)-3H-diazirin-3-yl]]phenoxy]acetyl - NT-II neurotoxin II     

Chemical constituents from Xylosma longifolia and their anti-tubercular activity

Two new glucosides, 3-methoxy-4-hydroxyphenylpropane-7,8-(6′-benzoyl-2′,1′-O-β-glucopyranosyl)-7,8,9-trio (1), and 2-hydroxyphenyl-4-caffeoyl-β-d-glucoside (2), together with seven known compounds were isolated from the stem bark of Xylosma longifolia (Flacourtiaceae). The structures of the isolates were established on the basis of their spectral data, including mass spectrometry and 2D-NMR. The compound 8-hydroxy-6-methoxy-pentylisocoumarin (3) exhibited an MIC value of 40.5 μg/mL against M. tuberculosis.     

Detection of mutator subpopulations in Salmonella typhimurium LT2 by reversion of his alleles

Defects in the methyl-directed mismatch repair lead to both the hypermutability phenotype and removal of a barrier to genetic exchange between species. Mutator bacteria carrying such defects occur frequently among bacterial pathogens, suggesting that subpopulations of mutators are contained within pathogen clones and give rise to the genetic variants that are acted upon by selective forces to allow survival or successful infection. We report here on the detection of the mutator subpopulation in Salmonella typhimurium and determination of its frequency in laboratory cultures. The analysis involved screening for mutators among revertants of S. typhimurium histidine auxotrophs selected for the His⁺ phenotype, since the frequency of mutators is expected to be increased in the selected mutant population they helped to spawn. The increases in spontaneous reversion of histidine mutations were first measured in isogenic strains carrying mismatch repair-defective mutH, mutL, mutS, or uvrD alleles, relative to their mismatch repair-proficient counterparts. Screening for the mutator phenotype in nearly 12,000 revertants of repair-proficient strains carrying his mutations highly stimulated for reversion in mutator backgrounds, the base substitution in hisG428 and frameshift in hisC3076, yielded five mutator strains (0.04%). the his⁺ reversion mutations contained within the newly-arisen mutator strains were characteristic of the predominant nucleotide changes expected in such mutators, as assessed by comparison with the spectra for reversion events in wild-type and mismatch correction-defective backgrounds. The results show that subpopulations of mutators, residing in normal populations at a finite frequency, can be culled from the culture by strong selection for a required phenotype. We calculate that the frequency of mutators in the unselected population of S. typhimurium is 1–4×10⁻⁶, an incidence of 10-fold lower than that expected based on studies of laboratory cultures of Escherichia coli.