Life‐history constraints in grassland plant species: a growth‐defence trade‐off is the norm

Plant growth can be limited by resource acquisition and defence against consumers, leading to contrasting trade‐off possibilities. The competition‐defence hypothesis posits a trade‐off between competitive ability and defence against enemies (e.g. herbivores and pathogens). The growth‐defence hypothesis suggests that strong competitors for nutrients are also defended against enemies, at a cost to growth rate. We tested these hypotheses using observations of 706 plant populations of over 500 species before and following identical fertilisation and fencing treatments at 39 grassland sites worldwide. Strong positive covariance in species responses to both treatments provided support for a growth‐defence trade‐off: populations that increased with the removal of nutrient limitation (poor competitors) also increased following removal of consumers. This result held globally across 4 years within plant life‐history groups and within the majority of individual sites. Thus, a growth‐defence trade‐off appears to be the norm, and mechanisms maintaining grassland biodiversity may operate within this constraint.     

Spatiotemporal Expression of Repulsive Guidance Molecules (RGMs) and Their Receptor Neogenin in the Mouse Brain

Neogenin has been implicated in a variety of developmental processes such as neurogenesis, neuronal differentiation, apoptosis, migration and axon guidance. Binding of repulsive guidance molecules (RGMs) to Neogenin inhibits axon outgrowth of different neuronal populations. This effect requires Neogenin to interact with co-receptors of the uncoordinated locomotion-5 (Unc5) family to activate downstream Rho signaling. Although previous studies have reported RGM, Neogenin, and/or Unc5 expression, a systematic comparison of RGM and Neogenin expression in the developing nervous system is lacking, especially at later developmental stages. Furthermore, information on RGM and Neogenin expression at the protein level is limited. To fill this void and to gain further insight into the role of RGM-Neogenin signaling during mouse neural development, we studied the expression of RGMa, RGMb, Neogenin and Unc5A-D using in situ hybridization, immunohistochemistry and RGMa section binding. Expression patterns in the primary olfactory system, cortex, hippocampus, habenula, and cerebellum were studied in more detail. Characteristic cell layer-specific expression patterns were detected for RGMa, RGMb, Neogenin and Unc5A-D. Furthermore, strong expression of RGMa, RGMb and Neogenin protein was found on several major axon tracts such as the primary olfactory projections, anterior commissure and fasciculus retroflexus. These data not only hint at a role for RGM-Neogenin signaling during the development of different neuronal systems, but also suggest that Neogenin partners with different Unc5 family members in different systems. Overall, the results presented here will serve as a framework for further dissection of the role of RGM-Neogenin signaling during neural development.     

Escherichia coli S-adenosylmethionine decarboxylase. Subunit structure, reductive amination, and NH2-terminal sequences

S-Adenosylmethionine decarboxylase is one of a small group of enzymes that use a pyruvoyl residue as a cofactor. Histidine decarboxylase from Lactobacillus 30a, the best studied pyruvoyl-containing enzyme, has an (alpha beta)6 subunit structure with the pyruvoyl moiety linked through an amide bond to the NH2-terminal of the larger alpha subunit (Recsei, P. A., Huynh, Q. K., and Snell, E. E. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 973-977). To examine potential structural analogies between the two enzymes, we have isolated and partially characterized S-adenosylmethionine decarboxylase. The purified enzyme comprises equimolar amounts of two subunits of Mr = 14,000 and 19,000 (by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and has a native molecular weight of 136,000 (by gel filtration). Approximately 4 mol of [methyl-3H] adenosylmethionine are incorporated per mol of enzyme (Mr = 136,000) when the enzyme is inactivated with this substrate and NaCNBH3. These data suggest an (alpha beta)4 structure with 1 pyruvoyl residue for each alpha beta pair. The two subunits have been separated by reversed-phase high performance liquid chromatography after reduction and carboxymethylation. The smaller subunit (beta) has a free amino terminus. The amino terminus of the larger subunit (alpha) appears to be blocked by a pyruvoyl group; this subunit can be sequenced only after this group is converted to an alanyl residue by reduction with sodium cyanoborohydride in the presence of ammonium acetate. This work suggests that S-adenosylmethionine decarboxylase is structurally much more similar to histidine decarboxylase than previously thought.     

Torres Strait Islanders Stories from an Exhibition

Preparations for a centenary exhibition to mark the 1898 Cambridge Anthropological Expedition to the Torres Strait incorporated cross-cultural collaborative work, reflecting the changing roles of museums as sites for contact and research combining curatorial expertise and indigenous knowledge. Specific objects in the collections of the University of Cambridge Museum of Archaeology and Anthropology continue to be active intermediaries in the relationship between museum staff and Torres Strait Islanders and the museum itself has become an important field site. This paper provides an ethnography of the process of creating the exhibition and explores different ways that many of the objects displayed have resonance for Islanders today.     

Dissecting the roles of Cse1 and Nup2 in classical NLS‐cargo release in vivo

The importin α/β transport machinery mediates the nuclear import of cargo proteins that bear a classical nuclear localization sequence (cNLS). These cargo proteins are linked to the major nuclear protein import factor, importin‐β, by the importin‐α adapter, after which cargo/carrier complexes enter the nucleus through nuclear pores. In the nucleus, cargo is released by the action of RanGTP and the nuclear pore protein Nup2, after which the importins are recycled to the cytoplasm for further transport cycles. The nuclear export of importin‐α is mediated by Cse1/CAS. Here, we exploit structures of functionally important complexes to identify residues that are critical for these interactions and provide insight into how cycles of protein import and recycling of importin‐α occur in vivo using a Saccharomyces cerevisiae model. We examine how these molecular interactions impact protein localization, cargo import, function and complex formation. We show that reversing the charge of key residues in importin‐α (Arg44) or Cse1 (Asp220) results in loss of function of the respective proteins and impairs complex formation both in vitro and in vivo. To extend these results, we show that basic residues in the Nup2 N‐terminus are required for both Nup2 interaction with importin‐α and Nup2 function. These results provide a more comprehensive mechanistic model of how Cse1, RanGTP and Nup2 function in concert to mediate cNLS‐cargo release in the nucleus.     

A practical guide to measuring functional indicators and traits in biocrusts

Biocrusts are multifunctional communities that are increasingly being used to restore degraded or damaged ecosystems. Concurrently, restoration science is shifting away from the use of purely structural metrics, such as relative abundance, to more functional approaches. Although biocrust restoration technology is advancing, there is a lack of readily available information on how to monitor biocrust functioning and set appropriate restoration goals. We therefore compiled a selection of 22 functional indicators that can be used to monitor biocrust functions, such as CO₂ exchange as an indicator of productivity or soil aggregate stability as a proxy for erosion resistance. We describe the functional importance of each indicator and the available protocols with which it may be measured. The majority of indicators can be measured as a functional trait of species by using patches of biocrust or cultures that contain only one species. Practitioners wishing to track the multifunctionality of an entire biocrust community would be advised to choose one indicator from each broad functional group (erosion resistance, nutrient accumulation, productivity, energy balance, hydrology), whereas a targeted approach would be more appropriate for projects with a key function of interest. Because predisturbance data are rarely available for biocrust functions, restoration goals can be based on a closely analogous site, literature values, or an expert elicitation process. Finally, we advocate for the establishment of a global trait database for biocrusts, which would reduce the damage resulting from repeated sampling, and provide a wealth of future research opportunities.