Genes involved in the activation of the bithorax complex ofDrosophila

Summary We have studied the genetic properties and developmental effects of several mutations, in eight different loci, which alter the specification of embryonic segments. All of the changes are related to the transformations caused by mutants of the bithorax complex.Several properties: the interactions of these mutants with different mutants of the bithorax complex, the interactions between themselves, the effect of changing dosages of their wildtype alleles and their response to ether induction of phenocopies permit one to distinguish between those mutations which affect activation of the bithorax genes in early embryogenesis and those which affect expression of the bithorax genes during development. This paper deals mainly with the Rg-bx locus and its interactions with other loci which affect segment specification.In particular two loci show genetic and developmental characteristics which seem to conform to those expected for a repressor coding gene (Polycomb) and for an inducer synthesizing gene (Rg-bx) active in a negative control system of the genes in the bithorax complex. A model for the interaction of the wildtype products of these genes to determine the segmental characteristics of both the thorax and abdomen is proposed.     

Genetic Analysis of the Effects of Polar Auxin Transport Inhibitors on Root Growth in Arabidopsis thaliana

Polar auxin transport inhibitors, including N-1-naphthylphthalamicacid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), have variouseffects on physiological and developmental events, such as theelongation and tropism of roots and stems, in higher plants.We isolated NPA-resistant mutants of Arabidopsis thaliana, withmutations designated pir1 and pir2, that were also resistantto TIBA. The mutations specifically affected the root-elongationprocess, and they were shown ultimately to be allelic to aux1and ein2, respectively, which are known as mutations that affectresponses to phytohormones. The mechanism of action of auxintransport inhibitors was investigated with these mutants, inrelation to the effects of ethylene, auxin, and the polar transportof auxin. With respect to the inhibition of root elongationin A. thaliana, we demonstrated that (1) the background levelof ethylene intensifies the effects of auxin transport inhibitors,(2) auxin transport inhibitors might act also via an inhibitorypathway that does not involve ethylene, auxin, or the polartransport of auxin, (3) the hypothesis that the inhibitory effectof NPA on root elongation is due to high-level accumulationof auxin as a result of blockage of auxin transport is not applicableto A. thaliana, and (4) in contrast to NPA, TIBA itself hasa weak auxin-like inhibitory effect. (Received April 12, 1996; Accepted September 2, 1996)     

Mutations in the SGR4, SGR5 and SGR6 Loci of Arabidopsis thaliana Alter the Shoot Gravitropism

Shoots of higher plants grow upward in response to gravity.To elucidate the molecular mechanism of this response, we haveisolated shoot gravitropism (sgr) mutants in Arabidopsis thaliana.In this report, we describe three novel mutants, sgr4-1, sgr5-1and sgr6-1 whose inflorescence stems showed abnormal gravitropicresponses as previously reported for sgr1, sgr2 and sgr3. Thesenew sgr mutations were recessive and occurred at three independentgenetic loci. The sgr4-1 mutant showed severe defect in gravitropismof both inflorescence stem and hypocotyl but were normal inroot gravitropism as were sgr1 and sgr2. The sgr5-1 and sgr6-1mutants showed reduced gravitropism only in inflorescence stemsbut normal in both hypocotyls and roots as sgr3. These resultssupport the hypothesis that some mechanisms of gravitropismare genetically different in these three organs in A. thaliana.In addition, these mutants showed normal phototropic responses,suggesting that SGR4, SGR5 and SGR6 genes are specifically involvedin gravity perception and/or gravity signal transduction forthe shoot gravitropic response. (Received November 21, 1996; Accepted February 17, 1997)     

High-Throughput Functional Analysis of the Synechococcus elongatus PCC 7942 Genome

Synechococcus elongatus PCC 7942 was the first cyanobacterialstrain to be reliably transformed by exogenously added DNA andhas become the model organism for cyanobacterial circadian rhythms.With a small genome (2.7 Mb) and well-developed genetic tools,PCC 7942 provides an exceptional opportunity to elucidate thecircadian mechanism through genetics. We describe a projectto create mutations in every locus of the genome, both to assayeach locus for its potential contribution to the circadian clockand to archive data for the cyanobacterial community. Cosmidclones that carry inserts of PCC 7942 DNA are saturated withtransposon insertions in vitro to provide sequencing templatesand substrates for mutagenesis of the PCC 7942 genome via homologousrecombination. We have mutagenized 53% of the chromosome from50 chromosome-bearing cosmids and identified the positions ofinsertions in 31 of those cosmids and the 46 kb plasmid, pANL.PCC 7942 mutants defective for 490 different genes have beenscreened for circadian phenotypes. Mutagenesis of three apparentlyessential loci, including clpPIIclpX, resulted in circadianphenotypes. We developed an effective antisense suppressionmethod to further the analysis of essential genes. When completed,the set of comprehensive mutations will provide the communitywith a unique resource whose impact will extend beyond circadianresearch.     

A Genome-wide Approach to Identify the Genes Involved in Biofilm Formation in E. coli

Biofilm forming cells are distinctive from the well-investigatedplanktonic cells and exhibit a different type of gene expression.Several new Escherichia coli genes related to biofilm formationhave recently been identified through genomic approaches suchas DNA microarray analysis. However, many others involved inthis process might have escaped detection due to poor expression,regulatory mechanism, or genetic backgrounds. Here, we screeneda collection of single-gene deletion mutants of E. coli named‘Keio collection’ to identify genes required forbiofilm formation. Of the 3985 mutants of non-essential genesin the collection thus examined, 110 showed a reduction in biofilmformation nine of which have not been well characterized yet.Systematic and quantitative analysis revealed the involvementof genes of various functions and reinforced the importancein biofilm formation of the genes for cell surface structuresand cell membrane. Characterization of the nine mutants of function-unknowngenes indicated that some of them, such as yfgA that geneticallyinteracts with a periplasmic chaperone gene surA together withyciB and yciM, might be required for the integrity of outermembrane.     

Nodulin gene expression in effective root nodules of white sweetclover (Melilotus alba Desr.) and in ineffective nodules elicited by mutant strains of Rhizobium meliloti

Fifteen nodulins and several nodule-stimulated gene productswere expressed in effective, nitrogen-fixing root nodules ofwhite sweetclover (Melilotus alba Desr. cv. U389), as determinedby two-dimensional gel electrophoresis of in vitro translationproducts. The number and gel position of eight leghaemoglobin(Lb) products, as well as a product tentatively identified asnodule-stimulated glutamine synthetase (GS), was similar toprevious reports of alfalfa (Medicago sativa L. cv. Iroquois)nodulins. Three mutants of Rhizobium meliloti, including anexoH mutant, a lipopolysaccharide mutant, and a nifH mutant,elicited ineffective sweetclover nodules blocked at empty (bacteria-free),partially infected, or fully infected stages of nodule development,respectively. In these ineffective nodules, the nodulin Nma30and nodule-stimulated NSTma42 were expressed early in development,while a group of four nodulins and two nodule-stimulated productswere intermediate in order of expression. Lb, GS and the latenodulin Nmal2a were expressed later, following infection. TheexoH mutant, Rm7154, appeared to be a leaky mutant, as a smallpercentage of the plants developed nitrogen-fixing nodules about4 weeks after inoculation. The sequential expression of a largenumber of nodulins and nodule-stimulated products, as well asthe availability of sweetclover nodulation mutants indicatesthat sweetclover is a useful diploid system for analysis ofhost genes essential to the Rhizobium/legume symbiosis. Key words: Nitrogen fixation, nodulation mutants, nodulins     

Impact of chloroplastic- and extracellular-sourced ROS on high light-responsive gene expression in Arabidopsis

The expression of 28 high light (HL)-responsive genes of Arabidopsiswas analysed in response to environmental and physiologicalfactors known to influence the expression of the HL-responsivegene, ASCORBATE PEROXIDASE2 (APX2). Most (81%) of the HL-responsivegenes, including APX2, required photosynthetic electron transportfor their expression, and were responsive to abscisic acid (ABA;68%), strengthening the impression that these two signals arecrucial in the expression of HL-responsive genes. Further, fromthe use of mutants altered in reactive oxygen species (ROS)metabolism, it was shown that 61% of these genes, includingAPX2, may be responsive to chloroplast-sourced ROS. In contrast,apoplastic/plasma membrane-sourced H₂O₂, in part directed bythe respiratory burst NADPH oxidases AtrbohD and AtrbohF, wasshown to be important only for APX2 expression. APX2 expressionin leaves is limited to bundle sheath parenchyma; however, forthe other genes in this study, information on their tissue specificityof expression is sparse. An analysis of expression in petioles,enriched for bundle sheath tissue compared with distal leafblade, in HL and control leaves showed that 25% of them had>10-fold higher expression in the petiole than in the leafblade. However, this did not mean that these petiole expressiongenes followed a pattern of regulation observed for APX2. Key words: Arabidopsis, chloroplast, excess light, gene expression, plasma membrane, reactive oxygen species, signalling     

The uaY positive control gene of Aspergillus nidulans: fine structure, isolation of constitutive mutants and reversion patterns

Summary The product of the uaY gene of Aspergillus nidulans is necessary for the expression of at least eight genes coding for enzymes and permeases of the purine utilisation pathway. A detailed fine structure map has been constructed of this gene involving 13 presumed point mutations and eight deletions. Gene conversion of these deletions was demonstrated. A technique was devised to select for constitutive mutations and two were obtained which map within the uaY gene. We have shown that the most centromere proximal allele reverts to a number of different phenotypes. The properties of this allele suggest that it may map in the open reading frame of the uaY gene, in a domain that could be altered in a way that would differentially affect the expression of genes under uaY control.