Opposite Effects of KCTD Subunit Domains on GABAB Receptor-mediated Desensitization

GABA_B receptors assemble from principle and auxiliary subunits. The principle subunits GABA_B1 and GABA_B2 form functional heteromeric GABA_B(1,2) receptors that associate with homotetramers of auxiliary KCTD8, -12, -12b, or -16 (named after their K⁺ channel tetramerization domain) subunits. These auxiliary subunits constitute receptor subtypes with distinct functional properties. KCTD12 and -12b generate desensitizing receptor responses while KCTD8 and -16 generate largely non-desensitizing receptor responses. The structural elements of the KCTDs underlying these differences in desensitization are unknown. KCTDs are modular proteins comprising a T1 tetramerization domain, which binds to GABA_B2, and a H1 homology domain. KCTD8 and -16 contain an additional C-terminal H2 homology domain that is not sequence-related to the H1 domains. No functions are known for the H1 and H2 domains. Here we addressed which domains and sequence motifs in KCTD proteins regulate desensitization of the receptor response. We found that the H1 domains in KCTD12 and -12b mediate desensitization through a particular sequence motif, T/NFLEQ, which is not present in the H1 domains of KCTD8 and -16. In addition, the H2 domains in KCTD8 and -16 inhibit desensitization when expressed C-terminal to the H1 domains but not when expressed as a separate protein in trans. Intriguingly, the inhibitory effect of the H2 domain is sequence-independent, suggesting that the H2 domain sterically hinders desensitization by the H1 domain. Evolutionary analysis supports that KCTD12 and -12b evolved desensitizing properties by liberating their H1 domains from antagonistic H2 domains and acquisition of the T/NFLEQ motif.     

Low levels of climate niche conservatism may explain clade diversity patterns in the South African genus Pelargonium (Geraniaceae)

? Premise of the study: Sharp climatic gradients in South Africa and in particular in the Cape Floristic Region (CFR) provide a diversity of niches over short distances that may have promoted ecological diversification in local clades. Here we measured the extent to which closely related species occupy divergent climates and test whether niche lability is correlated with higher species diversity in the genus. ? Method: We integrated phylogenetic information and environmental niche models (ENM) to assess the levels of climate niche conservatism. ENMs for 113 species of Pelargonium were calculated using maximum entropy. We used two tests, one assessing climate niche equivalency and the other testing niche similarity between sister species and within sections. We also examined whether niche similarity was correlated with phylogenetic relatedness across the genus. ? Key results: Niche similarity was mostly independent of phylogenetic relationships. Compared to random expectations, 23% of closely related species pairs had climate niches that were more similar, and only 6.5% were more disparate; the remaining 70% of comparisons had similarities that fell within random expectations. Similar trends were observed when analyses were restricted to only sister species pairs. Although the overall proportion of niche divergence was low, this was significantly related to sectional diversity. We also found a negative relationship between diversity and the proportion of random niches. ? Conclusions: Lack of widespread niche conservatism in a highly heterogeneous landscape and few instances of significant climate niche lability suggest that an adaptive divergence process was implicated in the Pelargonium radiation.     

Development and characterization of microsatellite markers for Berberis thunbergii (Berberidaceae)

? Premise of the study: Microsatellite markers were isolated and characterized in Berberis thunbergii, an invasive and ornamental shrub in the eastern United States, to assess genetic diversity among populations and potentially identify horticultural cultivars. ? Methods and Results: A total of 12 loci were identified for the species. Eight of the loci were polymorphic and were screened in 24 individuals from two native (Tochigi and Ibaraki prefectures, Japan) and one invasive (Connecticut, USA) population and 21 horticultural cultivars. The number of alleles per locus ranged from three to seven, and observed heterozygosity ranged from 0.048 to 0.636. ? Conclusions: These new markers will provide tools for examining genetic relatedness of B. thunbergii plants in the native and invasive range, including phylogeographic studies and assessment of rapid evolution in the invasive range. These markers may also provide tools for examining hybridization with other related species in the invasive range.     

GEOGRAPHIC DIFFERENCES IN SEXUAL REASSORTMENT IN RNA PHAGE

The genetic structure of natural bacteriophage populations is poorly understood. Recent metagenomic studies suggest that phage biogeography is characterized by frequent migration. Using virus samples mostly isolated in Southern California, we recently showed that very little population structure exists in segmented RNA phage of the Cystoviridae family due to frequent segment reassortment (sexual genetic mixis) between unrelated virus individuals. Here we use a larger genetic dataset to examine the structure of Cystoviridae phage isolated from three geographic locations in Southern New England. We document extensive natural variation in the physical sizes of RNA genome segments for these viruses. In addition, consistent with earlier findings, our phylogenetic analyses and calculations of linkage disequilibrium (LD) show no evidence of within‐segment recombination in wild populations. However, in contrast to the prior study, our analysis finds that reassortment of segments between individual phage plays a lesser role among cystoviruses sampled in New England, suggesting that the evolutionary importance of genetic mixis in Cystoviridae phage may vary according to geography. We discuss possible explanations for these conflicting results across the studies, such as differing local ecology and its impact on phage growth, and geographic differences in selection against hybrid phage genotypes.     

The antiquity of Madagascar’s grasslands and the rise of C4 grassy biomes

Aim Grasslands and savannas, which make up > 75% of Madagascar’s land area, have long been viewed as anthropogenically derived after people settled on the island c. 2 ka. We investigated this hypothesis and an alternative – that the grasslands are an insular example of the post‐Miocene spread of C₄ grassy biomes world‐wide. Location Madagascar, southern Africa, East Africa. Methods We compared the number of C₄ grass genera in Madagascar with that in southern and south‐central African floras. If the grasslands are recent we would expect to find fewer species and genera in Madagascar relative to Africa and for these species and genera to have very wide distribution ranges in Madagascar. Secondly, we searched Madagascan floras for the presence of endemic plant species or genera restricted to grasslands. We also searched for evidence of a grassland specialist fauna with species endemic to Madagascar. Plant and animal species endemic to C₄ grassy biomes would not be expected if these are of recent origin. Results Madagascar has c. 88 C₄ grass genera, including six endemic genera. Excluding African genera with only one or two species, Madagascar has 86.6% of southern Africa’s and 89.4% of south‐central Africa’s grass genera. C₄ grass species make up c. 4% of the flora of both Madagascar and southern Africa and species : genus ratios are similar (4.3 and 5.1, respectively). Turnover of grasses along geographical gradients follows similar patterns to those in South Africa, with Andropogoneae dominating in mesic biomes and Chlorideae in semi‐arid grassy biomes. At least 16 monocot genera have grassland members, many of which are endemic to Madagascar. Woody species in frequently burnt savannas include both Madagascan endemics and African species. A different woody flora, mostly endemic, occurs in less frequently burnt grasslands in the central highlands, filling a similar successional niche to montane C₄ grasslands in Africa. Diverse vertebrate and invertebrate lineages have grassland specialists, including many endemic to Madagascar (e.g. termites, ants, lizards, snakes, birds and mammals). Grassland use of the extinct fauna is poorly known but carbon isotope analysis indicates that a hippo, two giant tortoises and one extinct lemur ate C₄ or CAM (crassulacean acid metabolism) plants. Main conclusions The diversity of C₄ grass lineages in Madagascar relative to that in Africa, and the presence of plant and animal species endemic to Madagascan grassy biomes, does not fit the view that these grasslands are anthropogenically derived. We suggest that grasslands invaded Madagascar after the late Miocene, part of the world‐wide expansion of C₄ grassy biomes. Madagascar provides an interesting test case for biogeographical analysis of how these novel biomes assembled, and the sources of the flora and fauna that now occupy them. A necessary part of such an analysis would be to establish the pre‐settlement extent of the C₄ grassy biomes. Carbon isotope analysis of soil organic matter would be a feasible method for doing this.     

The ecological importance of insect frass: allelopathy in eucalypts

Our previously published experiments on allelopathic effects of insect frass in Eucalyptus communities (Silander et al. 1983) have been criticized on the grounds that our estimates of annual frass production were exscessive (Ohmart 1985). However, we spanned the entire array of estimates of frass fall available from eucalypt communities, and we demonstrated allelopathic effects at even the lowest levels suggested by Ohmart. We suggest that average values of frass fall per hectare are irrelevant because they ignore both large scale variation among sites in time and space, and small scale variation in patchiness of frass accumulation. At the ecological scales relevant to germinating seeds, frass concentrations in local pockets may be considerably higher than the averages calculated for the entire ground surface.     

Vacuolated plant cells as ideal osmometer: reversibility and limits of plasmolysis, and estimation of protoplasm volume in control and water-stress-tolerant cells

Abstract. The osmotic behaviour of vacuolated plant cells (adaxial epidermal cells of Allium cepa bulb scales, and epidermal as well as chloroplast containing subepidermal stem base cells of Pisum sativum) was studied over a wide range of CaCl₂ concentrations. The following results were obtained.

• a. Allium cepa and Pisum sativum plant cells behave as an ideal osmometer as far as plasmolytic contraction of the protoplast is concerned.
• b. The protoplasts of these cells could be plasmolysed to 15–45% of their original volume without the loss of membrane semi-permeability.
• c. Cells plasmolysed in 1.0 kmol m^?3 CaCl₂ could be completely deplasmolysed and upon deplasmolysis the cells resumed protoplasmic streaming.
• d. The above findings (a-c) indicate that during gradual plasmolysis and deplasmolysis membrane semi-permeability is maintained.
• e. At very high plasmolysing concentrations vacuoles covered with the tonoplast separated from the rest of the protoplasm in some cells whereas others showed systrophy. Extruded vacuoles were able to respond to osmotic shrinkage.
• f. The non-solvent space in Allium cells of about 3% also corresponded to the protoplasm volume calculated from the protoplast geometry (mean from results of direct measurement method and subtraction method).
• g. Subepidermal stem base cells of water-stress-tolerant Pisum plants had a 75% greater non-solvent space than the control cells indicating that a water-stress-tolerant cell may contain a larger amount of protoplasm and/or a vacuole with a higher content of colloidal material in the vacuole.
• h. Water-stress-tolerant cells showed greater tolerance to osmotic dehydration (volume reduction) than control cells.

     

SEEDLING RECRUITMENT LIMITATION IN WHITE CLOVER (TRIFOLIUM REPENS; LEGUMINOSAE)

White clover (Trifolium repens L.) is a stoloniferous clonal legume. Dynamics of white clover populations are controlled by the recruitment of both seedlings (genets) and node production (ramets). To understand the role of seedling dynamics in natural populations of white clover, the recruitment and mortality of seedlings in a lawn and pasture clover population were followed and the roles of biotic and abiotic factors in seedling recruitment and survival were assessed. Seedling recruitment was several orders of magnitude less than vegetative recruitment in both lawn and pasture populations. However, at least several new genets are added to these populations on a yearly basis. In both locations, physical disturbances may open sites for seed germination, as disturbed sites had higher seed germination rates than undisturbed sites. However, these sites were not favorable for long-term establishment due to such factors as frost upheaval. Therefore, there are trade-offs in safe site attributes for seed germination and establishment that strongly limit recruitment in natural populations of white clover.     

Ethical issues and GenomEUtwin.

The post-genomic era is witnessing a proliferation of large-scale and population based genetic and genomic research projects. Many countries have or are establishing research biobanks and, as with GenomEUtwin, there is great interest in building multinational projects that link genotypic and phenotypic information from different centers. Clearly, the conduct of these projects raises multiple ethical issues, and the knowledge generated will continually recast the ethical, legal and social implications (ELSI) of such research. Maximising the scientific profit from this work while minimizing the risks to the participants requires full integration of ethics components into the structure and functioning of these projects. GenomEUtwin is organized around five intellectual cores, including an Ethics Core which operates across the entire project. This paper describes the role of the Ethics Core and presents an overview of the guidelines on which the principles followed in GenomEUtwin are based. We outline the major ethical concerns of our project and highlight complexities arising from diverse national legislations. Finally, the role of empirically based ethics research is discussed for understanding the ethical, legal, social and economic implications of human genetics and genomics research.