Large scale patterns of genetic variation and differentiation in sugar maple from tropical Central America to temperate North America

© 2015 Vargas-Rodriguez et al. Background: Geological events in the latter Cenozoic have influenced the distribution, abundance and genetic structure of tree populations in temperate and tropical North America. The biogeographical history of temperate vegetation that spans large ranges of latitude is complex, involving multiple latitudinal shifts that might have occurred via different migration routes. We determined the regional structuring of genetic variation of sugar maple (Acer saccharum subsp. saccharum) and its only subspecies in tropical America (Acer saccharum subsp. skutchii) using nuclear and chloroplast data. The studied populations span a geographic range from Maine, USA (46°N), to El Progreso, Guatemala (15°N). We examined genetic subdivisions, explored the locations of ancestral haplotypes, analyzed genetic data to explore the presence of a single or multiple glacial refugia, and tested whether genetic lineages are temporally consistent with a Pleistocene or older divergence. Results: Nuclear and chloroplast data indicated that populations in midwestern USA and western Mexico were highly differentiated from populations in the rest of the sites. The time of the most recent common ancestor of the western Mexico haplotype lineage was dated to the Pliocene (5.9 Ma, 95 % HPD: 4.3-7.3 Ma). Splits during the Pleistocene separated the rest of the phylogroups. The most frequent and widespread haplotype occurred in half of the sites (Guatemala, eastern Mexico, southeastern USA, and Ohio). Our data also suggested that multiple Pleistocene refugia (tropics-southeastern USA, midwestern, and northeastern USA), but not western Mexico (Jalisco), contributed to post-glacial northward expansion of ranges. Current southern Mexican and Guatemalan populations have reduced population sizes, genetic bottlenecks and tend toward homozygosity, as indicated using nuclear and chloroplast markers. Conclusions: The divergence of western Mexican populations from the rest of the sugar maples likely resulted from orographic and volcanic barriers to gene flow. Past connectivity among populations in the southeastern USA and eastern Mexico and Guatemala possible occurred through gene flow during the Pleistocene. The time to the most common ancestor values revealed that populations from the Midwest and Northeast USA represented different haplotype lineages, indicating major divergence of haplotypes lineages before the Last Glacial Maximum and suggesting the existence of multiple glacial refugia

Unified 1-D Simulations of Gamma-Ray Line Emission from Type Ia Supernovae

The light curves of Type Ia Supernovae (SN Ia) are powered by gamma-rays emitted by the decay of radioactive elements such as $^{56}$Ni and its decay products. These gamma-rays are downscattered,absorbed, and eventually reprocessed into the optical emission which makes up the bulk of all supernova observations. Detection of the gamma-rays that escape the expanding star provide the only direct means to study this power source for SN Ia light curves. Unfortunately, disagreements between calculations for the gamma-ray lines have made it difficult to interpret any gamma-ray observations. Here we present a detailed comparison of the major gamma-ray line transport codes for a series of 1-dimensional Ia models. Discrepancies in past results were due to errors in the codes, and the corrected versions of the seven different codes yield very similar results. This convergence of the simulation results allows us to infer more reliable information from the current set of gamma-ray observations of SNe Ia. The observations of SNe 1986G, 1991T and 1998bu are consistent with explosion models based on their classification: sub-luminous, super-luminous and normally-luminous respectively.Comment: Accepted to the Astrophysical Journa

Proton Motive Force-Dependent Hoechst 33342 Transport by the ABC Transporter LmrA of Lactococcus lactis

The fluorescent compound Hoechst 33342 is a substrate for many multidrug resistance (MDR) transporters and is widely used to characterize their transport activity. We have constructed mutants of the adenosine triphosphate (ATP) binding cassette (ABC)-type MDR transporter LmrA of Lactococcus lactis that are defective in ATP hydrolysis. These mutants and wild-type LmrA exhibited an atypical behavior in the Hoechst 33342 transport assay. In membrane vesicles, Hoechst 33342 transport was shown to be independent of the ATPase activity of LmrA, and it was not inhibited by orthovanadate but sensitive to uncouplers that collapse the proton gradient and to N,N'-dicyclohexylcarbodiimide, an inhibitor of the F0F1-ATPase. In contrast, transport of Hoechst 33342 by the homologous, heterodimeric MDR transporter LmrCD showed a normal ATP dependence and was insensitive to uncouplers of the proton gradient. With intact cells, expression of LmrA resulted in an increased rate of Hoechst 33342 influx while LmrCD caused a decrease in the rate of Hoechst 33342 influx. Cellular toxicity assays using a triple knockout strain, i.e., L. lactis ΔlmrA ΔlmrCD, demonstrate that expression of LmrCD protects cells against the growth inhibitory effects of Hoechst 33342, while in the presence of LmrA, cells are more susceptible to Hoechst 33342. Our data demonstrate that the LmrA-mediated Hoechst 33342 transport in membrane vesicles is influenced by the transmembrane pH gradient due to a pH-dependent partitioning of Hoechst 33342 into the membrane.

A single active catalytic site is sufficient to promote transport in P-glycoprotein

P-glycoprotein (Pgp) is an ABC transporter responsible for the ATP-dependent efflux of chemotherapeutic compounds from multidrug resistant cancer cells. Better understanding of the molecular mechanism of Pgp-mediated transport could promote rational drug design to circumvent multidrug resistance. By measuring drug binding affinity and reactivity to a conformation-sensitive antibody we show here that nucleotide binding drives Pgp from a high to a low substrate-affinity state and this switch coincides with the flip from the inward- to the outward-facing conformation. Furthermore, the outward-facing conformation survives ATP hydrolysis: the post-hydrolytic complex is stabilized by vanadate, and the slow recovery from this state requires two functional catalytic sites. The catalytically inactive double Walker A mutant is stabilized in a high substrate affinity inward-open conformation, but mutants with one intact catalytic center preserve their ability to hydrolyze ATP and to promote drug transport, suggesting that the two catalytic sites are randomly recruited for ATP hydrolysis

New combinations in Ericameria (Asteraceae: Astereae)

Volume: 67Start Page: 109End Page: 11

Plants new and noteworthy for Louisiana and Mississippi

Volume: 2013-14Start Page: 1End Page:

The subtribal affinities of the genus Tetragonotheca (Asteraceae: Heliantheae)

Volume: 67Start Page: 405End Page: 41

Calandrinia ciliata (Portulacaceae) new to Louisiana

Volume: 2013-28Start Page: 1End Page: