High summer temperatures do not interact with fire to promote germination among seeds of Cistaceae: a reinterpretation of Luna (2020) with extra data on wet/dry conditions*

Plant Ecology - In a unique study, Luna (Luna, Sci Rep 10:1–10, 2020) examined the viability and germination of 12 hard-seeded Cistaceae in the Mediterranean Basin by alternating a prolonged...     

Temperature tracking by North Sea benthic invertebrates in response to climate change

Climate change is a major threat to biodiversity and distributions shifts are one of the most significant threats to global warming, but the extent to which these shifts keep pace with a changing climate is yet uncertain. Understanding the factors governing range shifts is crucial for conservation management to anticipate patterns of biodiversity distribution under future anthropogenic climate change. Soft‐sediment invertebrates are a key faunal group because of their role in marine biogeochemistry and as a food source for commercial fish species. However, little information exists on their response to climate change. Here, we evaluate changes in the distribution of 65 North Sea benthic invertebrate species between 1986 and 2000 by examining their geographic, bathymetric and thermal niche shifts and test whether species are tracking their thermal niche as defined by minimum, mean or maximum sea bottom (SBT) and surface (SST) temperatures. Temperatures increased in the whole North Sea with many benthic invertebrates showing north‐westerly range shifts (leading/trailing edges as well as distribution centroids) and deepening. Nevertheless, distribution shifts for most species (3.8–7.3 km yr^?1 interquantile range) lagged behind shifts in both SBT and SST (mean 8.1 km yr^?1), resulting in many species experiencing increasing temperatures. The velocity of climate change (VoCC) of mean SST accurately predicted both the direction and magnitude of distribution centroid shifts, while maximum SST did the same for contraction of the trailing edge. The VoCC of SBT was not a good predictor of range shifts. No good predictor of expansions of the leading edge was found. Our results show that invertebrates need to shift at different rates and directions to track the climate velocities of different temperature measures, and are therefore lagging behind most temperature measures. If these species cannot withstand a change in thermal habitat, this could ultimately lead to a drop in benthic biodiversity.     

Epstein-Barr virus isolates retain their capacity to evade T cell immunity through BNLF2a despite extensive sequence variation

The Epstein-Barr virus (EBV)-encoded immune evasion protein BNLF2a inhibits the transporter associated with antigen processing (TAP), thereby downregulating HLA class I expression at the cell surface. As a consequence, recognition of EBV-infected cells by cytotoxic T cells is impaired. Here, we show that sequence polymorphism of the BNLF2a protein is observed with natural EBV isolates, with evidence for positive selection. Despite these mutations, the BNLF2a variants efficiently reduce cell surface HLA class I levels. This conservation of BNLF2a function during evolution of EBV implies an important role for the viral TAP inhibitor in preventing T cell recognition during viral infection.     

A structural basis for varied αβ TCR usage against an immunodominant EBV antigen restricted to a HLA-B8 molecule

EBV is a ubiquitous and persistent human pathogen, kept in check by the cytotoxic T cell response. In this study, we investigated how three TCRs, which differ in their T cell immunodominance hierarchies and gene usage, interact with the same EBV determinant (FLRGRAYGL), bound to the same Ag-presenting molecule, HLA-B8. We found that the three TCRs exhibit differing fine specificities for the viral Ag. Further, via structural and biophysical approaches, we demonstrated that the viral Ag provides the greatest energetic contribution to the TCR-peptide-HLA interaction, while focusing on a few adjacent HLA-based interactions to further tune fine-specificity requirements. Thus, the TCR engages the peptide-HLA with the viral Ag as the main glue, such that neighboring TCR-MHC interactions are recruited as a supportive adhesive. Collectively, we provide a portrait of how the host's adaptive immune response differentially engages a common viral Ag.     

Soil warming alters nitrogen cycling in a New England forest: implications for ecosystem function and structure

Global climate change is expected to affect terrestrial ecosystems in a variety of ways. Some of the more well-studied effects include the biogeochemical feedbacks to the climate system that can either increase or decrease the atmospheric load of greenhouse gases such as carbon dioxide and nitrous oxide. Less well-studied are the effects of climate change on the linkages between soil and plant processes. Here, we report the effects of soil warming on these linkages observed in a large field manipulation of a deciduous forest in southern New England, USA, where soil was continuously warmed 5°C above ambient for 7 years. Over this period, we have observed significant changes to the nitrogen cycle that have the potential to affect tree species composition in the long term. Since the start of the experiment, we have documented a 45% average annual increase in net nitrogen mineralization and a three-fold increase in nitrification such that in years 5 through 7, 25% of the nitrogen mineralized is then nitrified. The warming-induced increase of available nitrogen resulted in increases in the foliar nitrogen content and the relative growth rate of trees in the warmed area. Acer rubrum (red maple) trees have responded the most after 7 years of warming, with the greatest increases in both foliar nitrogen content and relative growth rates. Our study suggests that considering species-specific responses to increases in nitrogen availability and changes in nitrogen form is important in predicting future forest composition and feedbacks to the climate system.     

Synthesis and isomerisation of two metallated N,O-complexes of ruthenium: Models for the Murai reaction

Two isomers of the N,O-coordinated acetylpyrrolyl complex [Ru(PPh₃)₂(CO)(NC₄H₃C(O)CH₃)H] {cis-N,H (1) and trans-N,H (2)} have been prepared as models for catalytic intermediates in the Murai reaction. Complex 2 isomerises to 1 upon heating via a dissociative pathway (ΔH^‡ = 195 ± 41 kJ mol⁻¹; ΔS^‡ = 232 ± 62 J mol⁻¹ K⁻¹); the mechanism of this process has been modeled using density functional calculations. Complex 2 displays moderate catalytic activity for the Murai coupling of 2′-methylacetophenone with trimethylvinylsilane, but 1 proved to be catalytically inactive under the same conditions.     

Periplasmic Domains of Pseudomonas aeruginosa PilN and PilO Form a Stable Heterodimeric Complex

Type IV pili (T4P) are bacterial virulence factors responsible for attachment to surfaces and for twitching motility, a motion that involves a succession of pilus extension and retraction cycles. In the opportunistic pathogen Pseudomonas aeruginosa, the PilM/N/O/P proteins are essential for T4P biogenesis, and genetic and biochemical analyses strongly suggest that they form an inner-membrane complex. Here, we show through co-expression and biochemical analysis that the periplasmic domains of PilN and PilO interact to form a heterodimer. The structure of residues 69-201 of the periplasmic domain of PilO was determined to 2.2 Å resolution and reveals the presence of a homodimer in the asymmetric unit. Each monomer consists of two N-terminal coiled coils and a C-terminal ferredoxin-like domain. This structure was used to generate homology models of PilN and the PilN/O heterodimer. Our structural analysis suggests that in vivo PilN/O heterodimerization would require changes in the orientation of the first N-terminal coiled coil, which leads to two alternative models for the role of the transmembrane domains in the PilN/O interaction. Analysis of PilN/O orthologues in the type II secretion system EpsL/M revealed significant similarities in their secondary structures and the tertiary structures of PilO and EpsM, although the way these proteins interact to form inner-membrane complexes appears to be different in T4P and type II secretion. Our analysis suggests that PilN interacts directly, via its N-terminal tail, with the cytoplasmic protein PilM. This work shows a direct interaction between the periplasmic domains of PilN and PilO, with PilO playing a key role in the proper folding of PilN. Our results suggest that PilN/O heterodimers form the foundation of the inner-membrane PilM/N/O/P complex, which is critical for the assembly of a functional T4P complex.