Rapid plant diversification: Planning for an evolutionary future

Systematic conservation planning is a branch of conservation biology that seeks to identify spatially explicit options for the preservation of biodiversity. Alternative systems of conservation areas are predictions about effective ways of promoting the persistence of biodiversity; therefore, they should consider not only biodiversity pattern but also the ecological and evolutionary processes that maintain and generate species. Most research and application, however, has focused on pattern representation only. This paper outlines the development of a conservation system designed to preserve biodiversity pattern and process in the context of a rapidly changing environment. The study area is the Cape Floristic Region (CFR), a biodiversity hotspot of global significance, located in southwestern Africa. This region has experienced rapid (post-Pliocene) ecological diversification of many plant lineages; there are numerous genera with large clusters of closely related species (flocks) that have subdivided habitats at a very fine scale. The challenge is to design conservation systems that will preserve both the pattern of large numbers of species and various natural processes, including the potential for lineage turnover. We outline an approach for designing a system of conservation areas to incorporate the spatial components of the evolutionary processes that maintain and generate biodiversity in the CFR. We discuss the difficulty of assessing the requirements for pattern versus process representation in the face of ongoing threats to biodiversity, the difficulty of testing the predictions of alternative conservation systems, and the widespread need in conservation planning to incorporate and set targets for the spatial components (or surrogates) of processes.

Function of the p86 subunit of eukaryotic initiation factor (iso)4F as a microtubule-associated protein in plant cells.

The isozyme form of eukaryotic initiation factor 4F [eIF-(iso)4F] from wheat germ is composed of a p28 subunit that binds the 7-methylguanine cap of mRNA and a p86 subunit having unknown function. The p86 subunit was found to have limited sequence similarity to a kinesin-like protein encoded by the katA gene of Arabidopsis thaliana. Native wheat germ eIF-(iso)4F and bacterially expressed p86 subunit and p86-p28 complex bound to taxol-stabilized maize microtubules (MTs) in vitro. Binding saturation occurred at 1 mol of p86 per 5-6 mol of polymerized tubulin dimer, demonstrating a substoichiometric interaction of p86 with MTs. No evidence was found for a direct interaction of the p28 subunit with MTs. Unlike kinesin, cosedimentation of eIF-(iso)4F with MTs was neither reduced by MgATP nor enhanced by adenosine 5'-[gamma-imido]triphosphate. Both p86 subunit and p86-p28 complex induced the bundling of MTs in vitro. The p86 subunit was immunolocalized to the cytosol in root maize cells and existed in three forms: fine particles, coarse particles, and linear patches. Many coarse particles and linear patches were colocalized or closely associated with cortical MT bundles in interphase cells. The results indicate that the p86 subunit of eIF-(iso)4F is a MT-associated protein that may simultaneously link the translational machinery to the cytoskeleton and regulate MT disposition in plant cells.

Identification of a small, very acidic constitutive nucleolar protein (NO29) as a member of the nucleoplasmin family

We report the discovery and molecular characterization of a small and very acidic nucleolar protein of an SDS/PAGE mobility corresponding to Mr 29,000 (NO29). The cDNA-deduced sequence of the Xenopus laevis protein defines a polypeptide of a calculated molecular mass of 20,121 and a pI of 3.75, with an extended acidic region near its C terminus, and is related to the major nucleolar protein, NO38, and the histone-binding protein, nucleoplasmin. This member of the nucleoplasmin family of proteins was immunolocalized to nucleoli in Xenopus oocytes and diverse somatic cells. Protein NO29 is associated with nuclear particles from Xenopus oocytes, partly complexed with protein NO38, and occurs in preribosomes but not in mature ribosomes. The location and the enormously high content of negatively charged amino acids lead to the hypothesis that NO29 might be involved in the nuclear and nucleolar accumulation of ribosomal proteins and the coordinated assembly of pre-ribosomal particles.

RNA is a structural element in retrovirus particles

A single retroviral protein, Gag, is sufficient for virus particle assembly. While Gag is capable of specifically packaging the genomic RNA into the particle, this RNA species is unnecessary for particle assembly in vivo. In vitro, nucleic acids profoundly enhance the efficiency of assembly by recombinant Gag proteins, apparently by acting as “scaffolding” in the particle. To address the participation of RNA in retrovirus assembly in vivo, we analyzed murine leukemia virus particles that lack genomic RNA because of a deletion in the packaging signal of the viral RNA. We found that these particles contain cellular mRNA in place of genomic RNA. This result was particularly evident when Gag was expressed by using a Semliki Forest virus-derived vector: under these conditions, the Semliki Forest virus vector-directed mRNA became very abundant in the cells and was readily identified in the retroviral virus-like particles. Furthermore, we found that the retroviral cores were disrupted by treatment with RNase. Taken together, the data strongly suggest that RNA is a structural element in retrovirus particles.

Airborne minerals and related aerosol particles: Effects on climate and the environment

Aerosol particles are ubiquitous in the troposphere and exert an important influence on global climate and the environment. They affect climate through scattering, transmission, and absorption of radiation as well as by acting as nuclei for cloud formation. A significant fraction of the aerosol particle burden consists of minerals, and most of the remainder— whether natural or anthropogenic—consists of materials that can be studied by the same methods as are used for fine-grained minerals. Our emphasis is on the study and character of the individual particles. Sulfate particles are the main cooling agents among aerosols; we found that in the remote oceanic atmosphere a significant fraction is aggregated with soot, a material that can diminish the cooling effect of sulfate. Our results suggest oxidization of SO2 may have occurred on soot surfaces, implying that even in the remote marine troposphere soot provided nuclei for heterogeneous sulfate formation. Sea salt is the dominant aerosol species (by mass) above the oceans. In addition to being important light scatterers and contributors to cloud condensation nuclei, sea-salt particles also provide large surface areas for heterogeneous atmospheric reactions. Minerals comprise the dominant mass fraction of the atmospheric aerosol burden. As all geologists know, they are a highly heterogeneous mixture. However, among atmospheric scientists they are commonly treated as a fairly uniform group, and one whose interaction with radiation is widely assumed to be unpredictable. Given their abundances, large total surface areas, and reactivities, their role in influencing climate will require increased attention as climate models are refined.

Production of infectious recombinant Moloney murine leukemia virus particles in BHK cells using Semliki Forest virus-derived RNA expression vectors.

We describe a heterologous, Semliki Forest virus (SFV)-driven packaging system for the production of infectious recombinant Moloney murine leukemia virus particles. The gag-pol and env genes, as well as a recombinant retrovirus genome (LTR-psi (+)-neoR-LTR), were inserted into individual SFV1 expression plasmids. Replication-competent RNAs were transcribed in vitro and introduced into the cytoplasm of BHK-21 cells using electroporation. The expressed Moloney murine leukemia virus structural proteins produced extracellular virus-like particles. In these particles the gag precursor was processed into mature products, indicating that the particles contained an active protease. The protease of the gag-pol fusion protein was also shown to be active in a trans-complementation assay using a large excess of Pr65gag. Moreover, the particles possessed reverse transcriptase (RT) activity as measured in an in vitro assay. Cotransfection of BHK-21 cells by all three SFV1 constructs resulted in the production of transduction-competent particles at 4 x 10(6) colony-forming units (cfu)/ml during a 5-hr incubation period. Altogether, 2.9 x 10(7) transduction-competent particles were obtained from about 4 x 10(6) transfected cells. Thus, this system represents the first RNA-based packaging system for the production of infectious retroviral particles. The facts that no helper virus could be detected in the virus stocks and that particles carrying the amphotropic envelope could be produced with similar efficiency as those that carry the ecotropic envelope make the system very interesting for gene therapy.