A dated phylogeny and collection records reveal repeated biome shifts in the African genus Coccinia (Cucurbitaceae)

Background: Conservatism in climatic tolerance may limit geographic range expansion and should enhance the effects of habitat fragmentation on population subdivision. Here we study the effects of historical climate change, and the associated habitat fragmentation, on diversification in the mostly sub-Saharan cucurbit genus Coccinia, which has 27 species in a broad range of biota from semi-arid habitats to mist forests. Species limits were inferred from morphology, and nuclear and plastid DNA sequence data, using multiple individuals for the widespread species. Climatic tolerances were assessed from the occurrences of 1189 geo-referenced collections and WorldClim variables. Results: Nuclear and plastid gene trees included 35 or 65 accessions, representing up to 25 species. The data revealed four species groups, one in southern Africa, one in Central and West African rain forest, one widespread but absent from Central and West African rain forest, and one that occurs from East Africa to southern Africa. A few individuals are differently placed in the plastid and nuclear (LFY) trees or contain two ITS sequence types, indicating hybridization. A molecular clock suggests that the diversification of Coccinia began about 6.9 Ma ago, with most of the extant species diversity dating to the Pliocene. Ancestral biome reconstruction reveals six switches between semi-arid habitats, woodland, and forest, and members of several species pairs differ significantly in their tolerance of different precipitation regimes. Conclusions: The most surprising findings of this study are the frequent biome shifts (in a relatively small clade) over just 6 - 7 million years and the limited diversification during and since the Pleistocene. Pleistocene climate oscillations may have been too rapid or too shallow for full reproductive barriers to develop among fragmented populations of Coccinia, which would explain the apparently still ongoing hybridization between certain species. Steeper ecological gradients in East Africa and South Africa appear to have resulted in more advanced allopatric speciation there

Analysis of LIDAR data fused with co-registered bands

Staphylococcus aureus and Streptococcus pyogenes, two important human pathogens, target host fibronectin (Fn) in their adhesion to and invasion of host cells1, 2. Fibronectin-binding proteins (FnBPs), anchored in the bacterial cell wall, have multiple Fn-binding repeats3 in an unfolded4, 5 region of the protein. The bacterium-binding site in the amino-terminal domain (1–5F1) of Fn contains five sequential Fn type 1 (F1) modules. Here we show the structure of a streptococcal (S. dysgalactiae) FnBP peptide (B3)6, 7 in complex with the module pair 1F12F1. This identifies 1F1- and 2F1-binding motifs in B3 that form additional antiparallel -strands on sequential F1 modules—the first example of a tandem -zipper. Sequence analyses of larger regions of FnBPs from S. pyogenes and S. aureus reveal a repeating pattern of F1-binding motifs that match the pattern of F1 modules in 1–5F1 of Fn. In the process of Fn-mediated invasion of host cells, therefore, the bacterial proteins seem to exploit the modular structure of Fn by forming extended tandem -zippers. This work is a vital step forward in explaining the full mechanism of the integrin-dependent2, 8 FnBP-mediated invasion of host cells

Plasticity of the PAS domain and a potential role for signal transduction in the histidine kinase DcuS

The mechanistic understanding of how membrane-embedded sensor kinases recognize signals and regulate kinase activity is currently limited. Here we report structure-function relationships of the multidomain membrane sensor kinase DcuS using solidstate NMR, structural modeling and mutagenesis. Experimental data of an individual cytoplasmic Per-Arnt-Sim (PAS) domain were compared to structural models generated in silico. These studies, together with previous NMR work on the periplasmic PAS domain, enabled structural investigations of a membrane-embedded 40-kDa construct by solid-state NMR, comprising both PAS segments and the membrane domain. Structural alterations are largely limited to protein regions close to the transmembrane segment. Data from isolated and multidomain constructs favor a disordered N-terminal helix in the cytoplasmic domain. Mutations of residues in this region strongly influence function, suggesting that protein flexibility is related to signal transduction toward the kinase domain and regulation of kinase activity