Hydrologic Regime Controls Soil Phosphorus Fluxes in Restoration and Undisturbed Wetlands

Many wetland restoration projects occur on former agricultural soils that have a history of disturbance and fertilization, making them prone to phosphorus (P) release upon flooding. To study the relationship between P release and hydrologic regime, we collected soil cores from three restoration wetlands and three undisturbed wetlands around Upper Klamath Lake in southern Oregon, U.S.A. Soil cores were subjected to one of three hydrologic regimes—flooded, moist, and dry—for 7.5 weeks, and P fluxes were measured upon reflooding. Soils from restoration wetlands released P upon reflooding regardless of the hydrologic regime, with the greatest releases coming from soils that had been flooded or dried. Undisturbed wetland soils released P only after drying. Patterns in P release can be explained by a combination of physical and biological processes, including the release of iron‐bound P due to anoxia in the flooded treatment and the mineralization of organic P under aerobic conditions in the dry treatment. Higher rates of soil P release from restoration wetland soils, particularly under flooded conditions, were associated with higher total P concentrations compared with undisturbed wetland soils. We conclude that maintaining moist soil is the means to minimize P release from recently flooded wetland soils. Alternatively, prolonged flooding provides a means of liberating excess labile P from former agricultural soils while minimizing continued organic P mineralization and soil subsidence.     

Isolation of Naturally Occurring Viruses of the Murine Leukemia Virus Group in Tissue Culture

A tissue culture cell system for isolation and identification of members of the murine leukemia virus group (the complement fixation for murine leukemia test) was modified to permit the isolation of naturally occurring virus from leukemic and normal mice. The important factors for increasing the sensitivity of the test were the use of National Institutes of Health (NIH) strain Webster Swiss embryo cell cultures and the selection of rat-immune sera having complement-fixing antibodies to tissue culture antigens of both the Gross and FMR subgroups. In all, 163 strains of mouse leukemia virus, from 11 inbred mouse strains, have been isolated. Representative virus isolates were shown to possess the properties of the murine leukemia virus group; i.e., they were chloroform-sensitive, noncytopathic agents which replicated in mouse embryo tissue culture and produced group-reactive, complement-fixing antigen and budding C-type particles visible by electron microscopy. These viruses could serve as helpers in the rescue of Moloney sarcoma virus genome from non-producer hamster sarcoma cells, yielding pseudotypes. All of the 19 field isolates tested were neutralized by Gross passage A antiserum but not by potent antisera to the Moloney, Rauscher, and Friend strains. Virus was recovered regularly from embryos and from the plasma and spleen of adult mice of high leukemic strains. In low leukemic mouse strains, different patterns of virus detection were observed. In C3H/He mice, virus was occasionally present in embryos and was found in 40% of adult spleens. BALB/c mice were virus-negative as fetuses or weanlings, but spleens of more than half of the mice over 6 months of age yielded virus. NIH mice have never yielded virus. In reciprocal matings between AKR and BALB/c mice, virus recovery from embryos was maternally determined. The development of tissue culture isolation procedures made possible for the first time the application of classical infectious disease methods to the study of the natural history of murine leukemia virus infection.     

Structure and architecture of the maize genome

Maize (Zea mays or corn) plays many varied and important roles in society. It is not only an important experimental model plant, but also a major livestock feed crop and a significant source of industrial products such as sweeteners and ethanol. In this study we report the systematic analysis of contiguous sequences of the maize genome. We selected 100 random regions averaging 144 kb in size, representing about 0.6% of the genome, and generated a high-quality dataset for sequence analysis. This sampling contains 330 annotated genes, 91% of which are supported by expressed sequence tag data from maize and other cereal species. Genes averaged 4 kb in size with five exons, although the largest was over 59 kb with 31 exons. Gene density varied over a wide range from 0.5 to 10.7 genes per 100 kb and genes did not appear to cluster significantly. The total repetitive element content we observed (66%) was slightly higher than previous whole-genome estimates (58%-63%) and consisted almost exclusively of retroelements. The vast majority of genes can be aligned to at least one sequence read derived from gene-enrichment procedures, but only about 30% are fully covered. Our results indicate that much of the increase in genome size of maize relative to rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana) is attributable to an increase in number of both repetitive elements and genes.     

Structural, bioinformatic, and in vivo analyses of two Treponema pallidum lipoproteins reveal a unique TRAP transporter

Treponema pallidum, the bacterial agent of syphilis, is predicted to encode one tripartite ATP-independent periplasmic transporter (TRAP-T). TRAP-Ts typically employ a periplasmic substrate-binding protein (SBP) to deliver the cognate ligand to the transmembrane symporter. Herein, we demonstrate that the genes encoding the putative TRAP-T components from T. pallidum, tp0957 (the SBP), and tp0958 (the symporter), are in an operon with an uncharacterized third gene, tp0956. We determined the crystal structure of recombinant Tp0956; the protein is trimeric and perforated by a pore. Part of Tp0956 forms an assembly similar to those of "tetratricopeptide repeat" (TPR) motifs. The crystal structure of recombinant Tp0957 was also determined; like the SBPs of other TRAP-Ts, there are two lobes separated by a cleft. In these other SBPs, the cleft binds a negatively charged ligand. However, the cleft of Tp0957 has a strikingly hydrophobic chemical composition, indicating that its ligand may be substantially different and likely hydrophobic. Analytical ultracentrifugation of the recombinant versions of Tp0956 and Tp0957 established that these proteins associate avidly. This unprecedented interaction was confirmed for the native molecules using in vivo cross-linking experiments. Finally, bioinformatic analyses suggested that this transporter exemplifies a new subfamily of TPATs (TPR-protein-associated TRAP-Ts) that require the action of a TPR-containing accessory protein for the periplasmic transport of a potentially hydrophobic ligand(s).     

Ataxin1L Is a Regulator of HSC Function Highlighting the Utility of Cross-Tissue Comparisons for Gene Discovery

Hematopoietic stem cells (HSCs) are rare quiescent cells that continuously replenish the cellular components of the peripheral blood. Observing that the ataxia-associated gene Ataxin-1-like (Atxn1L) was highly expressed in HSCs, we examined its role in HSC function through in vitro and in vivo assays. Mice lacking Atxn1L had greater numbers of HSCs that regenerated the blood more quickly than their wild-type counterparts. Molecular analyses indicated Atxn1L null HSCs had gene expression changes that regulate a program consistent with their higher level of proliferation, suggesting that Atxn1L is a novel regulator of HSC quiescence. To determine if additional brain-associated genes were candidates for hematologic regulation, we examined genes encoding proteins from autism- and ataxia-associated protein–protein interaction networks for their representation in hematopoietic cell populations. The interactomes were found to be highly enriched for proteins encoded by genes specifically expressed in HSCs relative to their differentiated progeny. Our data suggest a heretofore unappreciated similarity between regulatory modules in the brain and HSCs, offering a new strategy for novel gene discovery in both systems.     

Data-Driven Modeling to Assess Receptivity for Rift Valley Fever Virus

Rift Valley Fever virus (RVFV) is an enzootic virus that causes extensive morbidity and mortality in domestic ruminants in Africa, and it has shown the potential to invade other areas such as the Arabian Peninsula. Here, we develop methods for linking mathematical models to real-world data that could be used for continent-scale risk assessment given adequate data on local host and vector populations. We have applied the methods to a well-studied agricultural region of California with 1 million dairy cattle, abundant and competent mosquito vectors, and a permissive climate that has enabled consistent transmission of West Nile virus and historically other arboviruses. Our results suggest that RVFV outbreaks could occur from February–November, but would progress slowly during winter–early spring or early fall and be limited spatially to areas with early increases in vector abundance. Risk was greatest in summer, when the areas at risk broadened to include most of the dairy farms in the study region, indicating the potential for considerable economic losses if an introduction were to occur. To assess the threat that RVFV poses to North America, including what-if scenarios for introduction and control strategies, models such as this one should be an integral part of the process; however, modeling must be paralleled by efforts to address the numerous remaining gaps in data and knowledge for this system.     

Biology and Functional Ecology of Equisetum with Emphasis on the Giant Horsetails

Horsetails are unique survivors of a very ancient group of vascular plants, the Sphenophyta, which has a history reaching back to the Upper Devonian. Despite the striking conservatism of Equisetum architecture and anatomy and the small number of species (15) in the modern flora, their ability to thrive under a wide range of conditions is remarkable. This is due to a diverse suite of adaptations that allow tolerance of disturbance, soil anoxia, high metals, and salinity, along with efficient nutrient uptake and nitrogen fixation. The giant horsetails represent the largest living Sphenophyta and provide insights into how their larger ancestors lived and how this ancient lineage has managed to survive in tropical regions.