Geminiviruses: Genome structure and gene function

The plant pathogenic single‐strand DNA‐containing geminiviruses have been the recent focus of intense investigation, owing both to their agronomic importance and to their potential as vectors for the expression of foreign genes in plants. Molecular genetic studies have provided detailed information on the genomic organization of many of these viruses. A greater genetic complexity has been demonstrated among the members of this viral family than had previously been suspected, as well as an apparently rapid rate of evolution of genetic diversity. We now recognize fundamental differences in the genome structure and organization of the whitefly‐ and leafhopper‐transmitted viruses, as well as among those geminiviruses infecting dicotyledonous or monocotyledonous hosts. This knowledge has provided new insights into the evolution of these viruses. The viral genes involved in replication and in systemic movement in the plant have been defined, and viral origins for single‐strand (ss) and double‐strand (ds) DNA replication have been mapped to small nucleotide regions. With the structural features of the viral genomes now well defined, current efforts are focused on elucidating the molecular aspects of viral gene regulation and interactions with host‐cell components that lead to the production of disease. Recent progress in determining the mechanism of replication and systemic movement and the contributions of these to symptom and disease development are discussed in the context of the potential for genetically engineering disease‐resistant plants.     

Characterization of fall armyworm mitochondrial DNA (Lepidoptera: Noctuidae)

Mitochondrial DNA from the fall armyworm, Spodoptera frugiperda (J.E. Smith), was cloned and characterized using restriction enzyme mapping. Genome size is approximately 16.3 kilobase (Kb), consistent with that of most animals. Three fragments, 8.1 Kb, 6.2 Kb, and 2.0 Kb, were produced by digestion with restriction enzyme Xbal and cloned into a pUC19 vector. Twenty-nine restriction enzymes were used to generate a detailed physical restriction enzyme map of the three cloned fragments. These data represent the first detailed characterization of a lepidopteran mitochondrial genome. © 1992 Wiley-Liss, Inc.     

Nuclear genome characterization of the carrageenophyteAgardhiella subulata (Rhodophyta)

DNA reassociation kinetics were used to determine nuclear genome organization and complexity inAgardhiella subulata (Gigartinales, Rhodophyta). Results indicate the presence of three second-order components corresponding to fast (22%), intermediate (68%) and slow (10%) fractions. Thus, the genome consists of 90% repetitive sequences. Microspectrophotoometry with the DNA-localizing fluorochrome DAPI was used to confirm ploidy level differences in the gametophytic and tetrasporophytic phases. Results indicate that meiosis occurs during tetrasporogenesis. Comparison of mean nuclear DNA (I_f) values to chicken erythrocytes (RBC) resulted in an estimate of 0.9 pg/2C genome forAgardhiella. Karyological studies using aceto-orcein revealed a chromosome complement of 2N = 44 in carposporangia and the presence of 22 bivalents during diakinesis of tetraspore mother cells.     

Genome analysis ofElymus angulatus andE. patagonicus (Poaceae) and their hybrids with N. and S. AmericanHordeum spp.

The results of genome analysis of five hybrids, viz.Elymus patagonicus ×Hordeum procerum, E. patagonicus ×H. tetraploidum, E. angulatus ×H. jubatum, E. angulatus ×H. lechleri, andE. angulatus ×H. parodii, are reported. The genomic constitution ofHordeum tetraploidum andH. jubatum is best given as H₁H₁H₂H₂, ofH. lechleri andH. parodii as H₁H₁H₂H₂H₄H₄, ofH. procerum as H₁H₁H₂H₂H₃H₃, and ofElymus patagonicus andE. angulatus as SSH₁H₁H₂H₂.     

Cloning and characterization of a linear 2.3 kb mitochondrial plasmid of maize

Summary A linear 2.3 kb DNA molecule found in maize mitochondria was cloned into pUC8. A natural deletion of this plasmid, found in cmsT and some N (fertile) types of maize plants, was mapped to one end of the plasmid. A minor sequence homology to S-2, another linear mitochondrial plasmid, was detected, as well as more significant sequence homology with chloroplast and maize nuclear DNA. Hybridization to teosinte mitochondrial DNA (mtDNA) revealed the presence of part of the maize plasmid in the high molecular weight mtDNA of the maize relatives. RNA dot hybridization indicates that the plasmid is transcribed in mitochondria. The termini of the 2.3 kb linear plasmid contain inverted repeated sequences; of the first 17 nucleotides of the termini, 16 are identical to the terminal inverted repeats of the linear S plasmids found in the mitochondria of cmsS maize plants.     

Trypanosoma brucei: analysis of relapsing populations in sensitive and resistant breeds of cattle

The clone DiTat 1.1 of Trypanosoma brucei brucei was injected into four bovids, and clones obtained from successive waves of parasitemia were used to study the expressed variant-specific surface glycoprotein repertoire. Twenty-four clones were obtained which could be classified into 12 different variable antigen types, in addition to the clone injected, using agglutination or immunofluorescence with monospecific antisera. The variable surface glycoproteins of the 25 clones were extracted using the detergent octyl-beta-D-glucopyranoside in the presence of the protease inhibitor, N-cbz-L-phenylalaninechloromethylketone. The molecular weights varied from 52,000 to 69,000 and the pI from 5.0 to 8.8. The virulence of 14 clones representing 13 variable antigen types was ascertained in mice. The mean survival time ranged from 20.5 to 43.0 days. Clones isolated from early peaks of parasitemia in the bovid were the most virulent while clones derived from later peaks were less virulent. It seems that organisms of diminishing virulence appear in bovids, leading to self-cure of the disease. All clones were sensitive to human serum in a blood infectivity inhibition test. Antibody against all virulent clones appeared in 20 cattle (10 Zebus, 10 Baoulés) which had been injected with T. brucei DiTat 1.1. There was no evidence for parasites of high or low virulence being preferentially expressed in resistant or sensitive hosts.     

Positioning of protein-coding genes on the soybean chloroplast genome

Seven major plastid protein encoding genes were positioned on the soybean chloroplast DNA by heterologous hybridization. These include the genes for the alpha, beta and epsilon subunits of the CF₁ component of ATP synthase (atpA, atpB and atpE respectively), for subunit III of the CF₀ component of ATP synthase (atpH), for the cytochrome f (cytF), for the ‘32 Kd’ thylakoid protein (psbA), and for the large subunit of ribulose-1,5-bisphosphate carboxylase-oxygenase (rbcL), all of which map in the large single copy region. The atpB, atpE and rbcL genes are located in the region adjacent to one of the segments of the inverted repeat. The genetic organization of the soybean chloroplast DNA is compared to that of other plastid genomes.     

玉米黄早4雄性不育系、保持系过氧化物酶同工酶的比较研究

在玉米黄早4雄性不育系、保持系的10个组织(叶、根、茎、芽鞘、胚轴、苞叶、穗轴、花丝、雌蕊、花药)中共检测出18种正、负极向过氧化物酶,其中有7个组织不育系与保持系间过氧化物酶没有差异,只有在3个组织中(叶、茎、花药)不育系与保持系间的过氧化物酶存在差异,说明玉米黄早4雄性不育系及保持系的过氧化物酶可能由细胞核基因编码。不育系与保持系个别组织内过氧化物酶存在差异,可能是由于核内编码过氧化物酶的基因表达异常所引起,而这种表达异常,可能是与不育系中不育细胞质基因调控核基因的表达有关。