Selecting representative model micro-organisms

Background  

Micro-biological research relies on the use of model organisms that act as representatives of their species or subspecies, these are frequently well-characterized laboratory strains. However, it has often become apparent that the model strain initially chosen does not represent important features of the species. For micro-organisms, the diversity of their genomes is such that even the best possible choice of initial strain for sequencing may not assure that the genome obtained adequately represents the species. To acquire information about a species' genome as efficiently as possible, we require a method to choose strains for analysis on the basis of how well they represent the species.     

Isolation of an actin polymerization stimulator from bovine thyroid plasma membranes

An actin polymerization stimulator was purified from bovine thyroid plasma membranes by DNase I affinity column chromatography. Although the molecular weight of the protein was about 42,000 (42K) by sodium dodecyl sulfate polyacrylamide gel electrophoresis, it did not comigrate with actin. In the presence of 30 mM KCl, the 42K protein facilitated formation of actin filaments when analyzed by a centrifugation method, accelerated the initial phase of actin polymerization as measured in an Ostwald viscometer and increased the length of filaments as shown by electron microscopy. The 42K protein also accelerated the initial phase of actin polymerization in the presence of 100 mM KCl and 2 mM MgCl₂ but did not affect the final viscosity. The effect of the 42K protein was diminished by 5 uM cytochalasin B or 1 uM cytochalasin D. This 42K protein may anchor actin filaments onto the thyroid plasma membrane.     

Production and Fungitoxicity of the Terpenoid Phytoalexins in Cotton Inoculated with Fusarium oxysporum f. sp. vasinfectum

Four terpenoid phytoalexins, desoxyhemigossypol (dHG), hemigossypol (HG), desoxyhemigossypol- 6-methyl ether (dMHG) and hemigossypol-6-methyl ether (MHG), were identified with HPLC analysis of extracts from the moderately Fusarium wilt resistant cotton var. TAMCOT CAMD-E ( Gossypium hirsutum ) inoculated with Fusarium oxysporum f. sp. vasinfectum (F. o. v.). Concentrations of dHG, HG, dMHG and MG in stem steles at 10 days after inoculation were 45.1, 175. 0, 38. 3 and 1. 6 (g g^–1 fresh tissue, respectively. The bioassays demonstrated that all four phytoalexins were toxic to F. o. v. The ED₅₀'s of dHG, dMHG and HG were calculated as 8. 8, 13. 4 and 29. 3 (g ml⁻¹, respectively. The very low solubility of MHG in the standard assay medium prevented the determination of its ED₅₀ value. Only dHG is water soluble at levels that appear necessary to act as an effective phytoalexin. At 30 μg ml⁻¹, dHG kills all conidia and mycelia of F. o. v . Viable propagules of F. o. v. were recovered from the steles of inoculated plants 10 days after inoculation; however, the pathogen was restricted to a zone 15 cm above the hypocotyl inoculation site. Thus, the fungistatic action of dHG appears to contribute to the resistance of cotton to Fusarium wilt by preventing the systemic distribution of F. o. v . propagules.     

Effects of dichloroacetate and glyoxylate on low density lipoprotein uptake and on growth of cultured fibroblasts

The effects of dichloroacetate, a known hypocholesterolemic agent, were studied in cultured growing and confluent human fibroblast cells. Microscopic examination showed no visible adverse effects of dichloroacetate on confluent cells during exposure to concentrations as high as 5 mM for 96 hr. Higher concentrations resulted in cell death after varying periods of incubation. There were no viable cells after 24 hr of exposure to 100 mM dichloroacetate. In contrast, much lower concentrations proved lethal to growing cells; cell growth, as determined by cell numbers at specified times after splitting, was suppressed by 1 mM dichloroacetate and 5 mM concentrations resulted in cell death. Similar effects were noted with glyoxylate. The hypocholesterolemic effect of dichloroacetate is probably not due to any effect on the low density lipoprotein pathway, since concentrations of up to 1 mM dichloroacetate did not affect the cellular binding and uptake of 125I-labeled low density lipoprotein. It is concluded that growing and rapidly metabolizing cells are much more sensitive to the toxic effects of dichloroacetate and glyoxylate than confluent cells.     

Antimicrobial terpenoids of Gossypium: 6-methoxygossypol and 6,6′-dimethoxygossypol

The triterpenoid aldehydes, gossypol (1), 6-methoxygossypol (2) and 6,6′-dimethoxygossypol (3); and the sesquiterpenoid aldehydes, hemigossypol (4) and methoxyhemigossypol (5), were isolated from 1-week-old roots of Gossypium hirsutum and G. barbadense and identified. This is the first report of 2 and 3 in nature and of 4 and 5 from healthy roots. Compounds 2 and 3 also constituted 30% of the total terpenoid aldehydes in the seeds of 1 cultivar of G. barbadense, but occurred only in trace quantities in those of G. hirsutum. Spectral data (UV, IR, NMR, MS) and proof of structure for 2 and 3 are presented.     

Supermodels: sorghum and maize provide mutual insight into the genetics of flowering time

Nested association mapping (NAM) offers power to dissect complex, quantitative traits. This study made use of a recently developed sorghum backcross (BC)-NAM population to dissect the genetic architecture of flowering time in sorghum; to compare the QTL identified with other genomic regions identified in previous sorghum and maize flowering time studies and to highlight the implications of our findings for plant breeding. A subset of the sorghum BC-NAM population consisting of over 1,300 individuals from 24 families was evaluated for flowering time across multiple environments. Two QTL analysis methodologies were used to identify 40 QTLs with predominately small, additive effects on flowering time; 24 of these co-located with previously identified QTL for flowering time in sorghum and 16 were novel in sorghum. Significant synteny was also detected with the QTL for flowering time detected in a comparable NAM resource recently developed for maize (Zea mays) by Buckler et al. (Science 325:714–718, 2009). The use of the sorghum BC-NAM population allowed us to catalogue allelic variants at a maximal number of QTL and understand their contribution to the flowering time phenotype and distribution across diverse germplasm. The successful demonstration of the power of the sorghum BC-NAM population is exemplified not only by correspondence of QTL previously identified in sorghum, but also by correspondence of QTL in different taxa, specifically maize in this case. The unification across taxa of the candidate genes influencing complex traits, such as flowering time can further facilitate the detailed dissection of the genetic control and causal genes.