Extramacrochaetae,a trans-acting gene of the achaete-scute complex of Drosophila involved in cell communication

Summary Phenotypic analyses of genetic combinations involving the gene extramacrochaetae (emc) reveal its participation in the differentiation of both sensory elements and wing veins. The study of near-amorphic alleles of emc in mitotitc recombination clones indicates that it also affects cell proliferation. These clones show abnormal sizes, shapes and spatial distribution. They differentiate extra sensory elements as well as extra veins. A gain of function mutation in the gene causes opposite phenotypes in both differentiation systems. The effects of the mutant on proliferation and patterning are consistent with the emc gene being involved in the transfer of information between neighbouring cells, which leads to the spatial expression of the achaetescute gene complex and genes involved in vein formation.     

A nomenclature for the genes encoding the chlorophylla/b-binding proteins of higher plants

We propose a nomenclature for the genes encoding the chlorophylla/b-binding proteins of the light-harvesting complexes of photosystem I and II. The genes encoding LHC I and LHC II polypeptides are namedLhca1 throughLhca4 andLhcb1 throughLhcb6, respectively. The proposal follows the general format recommended by the Commision on Plant Gene Nomenclature. We also present a table for the conversion of old gene names to the new nomenclature.     

Structural genes of glutamate 1-semialdehyde aminotransferase for porphyrin synthesis in a cyanobacterium and Escherichia coli

Summary In bacteria 5-aminolevulinate, the universal precursor in the biosynthesis of the porphyrin nucleus of hemes, chlorophylls and bilins is synthesised by two different pathways: in non-sulphur purple bacteria (Rhodobacter) or Rhizobium 5-aminolevulinate synthase condenses glycine and succinyl-CoA into 5-aminolevulinate as is the case in mammalian cells and yeast. In cyanobacteria, green and purple sulphur bacteria, as in chloroplasts of higher plants and algae a three step pathway converts glutamate into 5-aminolevulinate. The last step is the conversion of glutamate 1-semialdehyde into 5-aminolevulinate. Using a cDNA clone encoding glutamate 1-semialdehyde aminotransferase from barley, genes for this enzyme were cloned from Synechococcus PCC6301 and Escherichia coli and sequenced. The popC gene of E. coli, previously considered to encode 5-aminolevulinate synthase, appears to be a structural gene for glutamate 1-semialdehyde aminotransferase. Domains with identical amino acid sequences comprise 48% of the primary structure of the barley, cyanobacterial and putative E. coli glutamate 1-semialdehyde aminotransferases. The cyanobacterial and barley enzymes share 72% identical residues. The peptide containing a likely pyridoxamine phosphate binding lysine is conserved in all three protein sequences.     

Evidence of abortive recombination in ruv mutants of Escherichia coli K12

Summary Genetic recombination in Escherichia coli was investigated by measuring the effect of mutations in ruv and rec genes on F-prime transfer and mobilization of nonconjugative plasmids. Mutation of ruv was found to reduce the recovery of F-prime transconjugants in crosses with recB recC sbcA strains by about 30-fold and with recB recC sbcB sbcC strains by more than 300-fold. Conjugative plasmids lacking any significant homology with the chromosome were transferred normally to these ruv mutants. Mobilization of the plasmid cloning vectors pHSG415, pBR322, pACYC184 and pUC18 were reduced by 20- to 100-fold in crosses with ruv rec ⁺ sbc ⁺ strains, depending on the plasmid used. Recombinant plasmids carrying ruv ⁺ were transferred efficiently. With both F-prime transfer and F-prime cointegrate mobilization, the effect of ruv was suppressed by inactivating recA. It is proposed that the failure to recover transconjugants in ruv recA ⁺strains is due to abortive recombination and that the ruv genes define activities which function late in recombination to help convert recombination intermediates into viable products.     

Nucleotide sequence of the fixABC region of Azorhizobium caulinodans ORS571: similarity of the fixB product with eukaryotic flavoproteins, characterization of fixX, and identification of nifW.

Summary The nucleotide sequence of a 4.1 kb DNA fragment containing the fixABC region of Azorhizobium caulinodans was established. The three gene products were very similar to the corresponding polypeptides of Rhizobium meliloti. The C-terminal domains of both fixB products displayed a high degree of similarity with the -subunits of rat and human electron transfer flavoproteins, suggesting a role for the FixB protein in a redox reaction. Two open reading frames (ORF) were found downstream of fixC. The first ORF was identified as fixX on the basis of sequence homology with fixX from several Rhizobium and Bradyrhizobium strains. The second ORF potentially encoded a 69 amino acid product and was found to be homologous to a DNA region in the Rhodobacter capsulatus nif cluster I. Insertion mutagenesis of the A. caulinodans fixX gene conferred a Nif^– phenotype to bacteria grown in the free-living state and a Fix^– phenotype in symbiotic association with the host plant Sesbania rostrata. A crude extract from the fixX mutant had no nitrogenase activity. Furthermore, data presented in this paper also indicate that the previously identified nifO gene located upstream of fixA was probably a homologue of the nifW gene of Klebsiella pneumoniae and Azotobacter vinelandii.     

Genetic linkage between C-bands and storage protein genes in chromosome 1B of tetraploid wheat

Summary Genetic mapping of polymorphic C-bands allows direct comparisons between genetic and physical maps. Eleven C-bands and two seed storage protein genes on chromosome 1B, polymorphic between Langdon durum and four accessions of T. dicoccoides, were used to study the distribution of recombination along the entire length of the chromosome. Recombination in the short arm was almost completely restricted to the satellite, two-thirds of the arm's length from the centromere; the Gli-B1 gene was found to be tightly linked to the telomeric C-band. In the long arm, the distal 51.4% of the arm accounted for 88% of recombination; the proximal half of the arm accounted for the remaining 12%. While the amount of crossing-over differed significantly between the four T. dicoccoides 1B chromosomes, there were no significant differences in the relative distributions of crossing-over along the chromosome. Consequently, the genetic maps obtained from the four individual T. dicoccoides chromosomes were combined to yield a consensus map of 14 markers (including the centromere) for the chromosome.     

New disease resistance genes in soybean against Pseudomonas syringae pv glycinea: evidence that one of them interacts with a bacterial elicitor

Summary Soybean [Glycine max (L.) Merr.] cultivars Flambeau and Merit differed in their resistance to Pseudomonas syringae pv glycinea (Psg) race 4, carrying each of four different avirulence (avr) genes cloned from Psg or the related bacterium, Pseudomonas syringae pv tomato. Segregation data for F₂ and F₃ progeny of Flambeau x Merit crosses indicated that single dominant and nonallelic genes account for resistance to Psg race 4, carrying avirulence genes avrA, avrB, avrC, or avrD. Segregants were also recovered that carried all four or none of the disease resistance genes. One of the disease resistance genes (Rpg1, complementing bacterial avirulence gene B) had been described previously, but the other three genes — designated Rpg2, Rpg3, and Rpg4 — had not here to fore been defined. Rpg3 and Rpg4 are linked (40.5 ± 3.2 recombination units). Rpg4 complements avrD, cloned from Pseudomonas syringae pv tomato, but a functional copy of this avirulence gene has not thus far been observed in Pseudomonas syringae pv glycinea. Resistance gene Rpg4 therefore may account in part for the resistance of soybean to Pseudomonas syringae pv tomato and other pathogens harboring avrD.     

Efficient production of wheat-barley hybrids and preferential elimination of barley chromosomes

Summary Intergeneric hybridization between four common wheat cultivars, Triticum aestivum L. cultivars Chinese Spring, Norin 12, Norin 61, and Shinchunaga, and cultivated barley, Hordeum vulgare L. cultivars Betzes, Nyugoruden, Harunanijou, and Kinai 5 were carried out in a greenhouse under 15 – 20 °C and long-day (15 h) photoperiod conditions. Two days prior to pollination, a 100 mg/1 2,4-D solution was injected into wheat stems. Among wheat cultivars, Norin 12, Norin 61, and Shinchunaga showed higher crossabilities than that of Chinese Spring, suggesting the presence of crossability gene(s) other than the kr system of Chinese Spring. Variation was also found among the barley cultivars as male parents. Betzes barley showed the highest crossability with wheat. Thus, the cross Norin 12×Betzes showed the highest crossability (8.25%), followed by Norin 61 ×Betzes (6.04%), Shinchunaga×Betzes (5.00%), and Shinchunaga×Kinai 5 (5.00%). The embryos were rescued by culture at 15–20 days after pollination. Seventyfour plants were obtained from 82 embryos. The morphology of the hybrid plants resembled that of wheat parents. Among 60 seedlings observed, 28 had 28 chromosomes, 8 had 21, 23 had aneuploid numbers of chromosomes (22–27), and 1 had 29 chromosomes. About half of the aneuploid hybrids showed mosaicism for chromosome number. By analyzing five isozyme markers of barley chromosomes, the chromosome constitutions of the aneuploid hybrids were determined. Barley chromosomes 1 and 5 were found to be preferentially eliminated in the hybrids, while chromosomes 2 and 4 were eliminated infrequently. The conditions and genetic factors for high crossability and the tendency of barley chromosome elimination are discussed.     

C1 metabolism inParacoccus denitrificans: Genetics ofParacoccus denitrificans

Paracoccus denitrificans is able to grow on the C₁ compounds methanol and methylamine. These compounds are oxidized to formaldehyde which is subsequently oxidized via formate to carbon dioxide. Biomass is produced by carbon dioxide fixation via the ribulose biphosphate pathway. The first oxidation reaction is catalyzed by the enzymes methanol dehydrogenase and methylamine dehydrogenase, respectively. Both enzymes contain two different subunits in an ₂₂ configuration. The genes encoding the subunits of methanol dehydrogenase (moxF andmoxI) have been isolated and sequenced. They are located in one operon together with two other genes (moxJ andmoxG) in the gene ordermoxFJGI. The function of themoxJ gene product is not yet known.MoxG codes for a cytochromec _551i , which functions as the electron acceptor of methanol dehydrogenase. Both methanol dehydrogenase and methylamine dehydrogenase contain PQQ as a cofactor. These so-called quinoproteins are able to catalyze redox reactions by one-electron steps. The reaction mechanism of this oxidation will be described. Electrons from the oxidation reaction are donated to the electron transport chain at the level of cytochromec. P. denitrificans is able to synthesize at least 10 differentc-type cytochromes. Five could be detected in the periplasm and five have been found in the cytoplasmic membrane. The membrane-bound cytochromec ₁ and cytochromec ₅₅₂ and the periplasmic-located cytochromec ₅₅₀ are present under all tested growth conditions. The cytochromesc _551i andc _553i , present in the periplasm, are only induced in cells grown on methanol, methylamine, or choline. The otherc-type cytochromes are mainly detected either under oxygen limited conditions or under anaerobic conditions with nitrate as electron acceptor or under both conditions. An overview including the induction pattern of allP. denitrificans c-type cytochromes will be given. The genes encoding cytochromec ₁, cytochromec ₅₅₀, cytochromec _551i , and cytochromec _553i have been isolated and sequenced. By using site-directed mutagenesis these genes were mutated in the genome. The mutants thus obtained were used to study electron transport during growth on C₁ compounds. This electron transport has also been studied by determining electron transfer rates inin vitro experiments. The exact pathways, however, are not yet fully understood. Electrons from methanol dehydrogenase are donated to cytochromec _551i . Further electron transport is either via cytochromec ₅₅₀ or cytochromec _553i to cytochromeaa ₃. However, direct electron transport from cytochromec _551i to the terminal oxidase might be possible as well. Electrons from methylamine dehydrogenase are donated to amicyanin and then via cytochromec ₅₅₀ to cytochromeaa ₃, but other routes are used also.P. denitrificans is studied by several groups by using a genetic approach. Several genes have already been cloned and sequenced and a lot of mutants have been isolated. The development of a host/vector system and several techniques for mutation induction that are used inP. denitrificans genetics will be described.     

Identification of novel genes specifically expressed in Chlamydomonas reinhardtii zygotes

The maturation of zygotes formed by the fusion of two gametes is the essential part of the diploid phase of the Chlamydomonas reinhardtii sexual life cycle and results in mature zygotes competent to germinate. To understand the molecular mechanisms underlying zygote maturation and the attainment of competence for germination we isolated genomic clones representing three different genes that are specifically expressed in Chlamydomonas reinhardtii zygotes. Accumulation of the RNAs started more than 24 h after mating, setting these genes apart from genes expressed in young zygotes [9]. Upon light-induced germination of zygotes, the mRNAs disappeared. The patterns of RNA accumulation and disappearance were gene-specific and suggested a function of these genes in maturation and/or in initial steps of germination.