Arabidopsis sucrose transporter AtSUC1 is important for pollen germination and sucrose-induced anthocyanin accumulation

The Arabidopsis (Arabidopsis thaliana) sucrose transporter AtSUC1 (At1g71880) is highly expressed in pollen; however, its function has remained unknown. Here, we show that suc1 mutant pollen is defective in vivo, as evidenced by segregation distortion, and also has low rates of germination in vitro. AtSUC1-green fluorescent protein was localized to the plasma membrane in pollen tubes. AtSUC1 is also expressed in roots and external application of sucrose increased AtSUC1 expression in roots. AtSUC1 is important for sucrose-dependent signaling leading to anthocyanin accumulation in seedlings. suc1 mutants accumulated less anthocyanins in response to exogenous sucrose or maltose and microarray analysis revealed reduced expression of many genes important for anthocyanin biosynthesis. The results indicate that AtSUC1 is important for sugar signaling in vegetative tissue and for normal male gametophyte function.     

Studies in conservation genetics of tarpon (Megalops atlanticus) — V. Isolation and characterization of microsatellite loci

The tarpon, Megalops atlanticus, supports important recreational fisheries in the Atlantic Ocean, Caribbean Sea and Gulf of Mexico. Declines in segments of these fisheries have prompted questions concerning genetic stock structure in this species. Preparatory to a survey of genetic variation in tarpon, 15 microsatellite markers were isolated. The number of alleles per locus ranged from two to 10 and observed heterozygosity ranged from 0.091 to 0.765, providing potentially useful markers for the detection of within‐ and among‐population genetic variability.     

Explaining the coexistence of asexuals with their sexual progenitors: no evidence for general-purpose genotypes in obligate parthenogens of the peach-potato aphid, Myzus persicae

In parthenogens, selection acts on entire genotypes rather than individual alleles. The general‐purpose genotype hypothesis (GPG) predicts that temporally variable environments select for clones with broad ecological tolerances. These general‐purpose genotypes should exhibit low fitness variance and high geometric mean fitness across environments. We tested this hypothesis by comparing the fitness of obligately and cyclically parthenogenetic genotypes of the peach‐potato aphid, Myzus persicae, on three unrelated host plants. We found genetic variation for the relative performance on different hosts, but no difference in geometric mean fitness between obligate and cyclical parthenogens. Thus, for an environmental variable of major importance to aphids, the GPG hypothesis was not supported. In addition, the lack of an overall fitness difference between reproductive modes suggests that cyclical parthenogens incur no cost of polyphenism, but neither can they compensate for the cost of sex during the parthenogenetic phase of their life cycle.     

Presence-only data and the em algorithm

Summary .  In ecological modeling of the habitat of a species, it can be prohibitively expensive to determine species absence. Presence-only data consist of a sample of locations with observed presences and a separate group of locations sampled from the full landscape, with unknown presences. We propose an expectation–maximization algorithm to estimate the underlying presence–absence logistic model for presence-only data. This algorithm can be used with any off-the-shelf logistic model. For models with stepwise fitting procedures, such as boosted trees, the fitting process can be accelerated by interleaving expectation steps within the procedure. Preliminary analyses based on sampling from presence–absence records of fish in New Zealand rivers illustrate that this new procedure can reduce both deviance and the shrinkage of marginal effect estimates that occur in the naive model often used in practice. Finally, it is shown that the population prevalence of a species is only identifiable when there is some unrealistic constraint on the structure of the logistic model. In practice, it is strongly recommended that an estimate of population prevalence be provided.     

Gonadectomy negatively impacts social behavior of adolescent male primates

Social behavior changes dramatically during primate adolescence. However, the extent to which testosterone and other gonadal hormones are necessary for adolescent social behavioral development is unknown. In this study, we determined that gonadectomy significantly impairs social dominance in naturalistic settings and changes reactions to social stimuli in experimental settings. Rhesus macaques were castrated (n =  6) or sham operated (n = 6) at age 2.4 years, group-housed for 2 years, and ethograms were collected weekly. During adolescence the gonadally intact monkeys displayed a decrease in subordinate behaviors and an increase in dominant behaviors, which ultimately related to a rise in social status and rank in the dominance hierarchy. We measured monkey's reactions to emotional faces (fear, threat, neutral) of conspecifics of three ages (adult, peer, infant). Intact monkeys were faster to retrieve a treat in front of a threatening or infant face, while castrated monkeys did not show a differential response to different emotional faces or ages. No group difference in reaction to an innate fear-eliciting object (snake) was found. Approach and proximity responses to familiar vs unfamiliar conspecifics were tested, and intact monkeys spent more time proximal to a novel conspecific as compared to castrates who tended to spend more time with a familiar conspecific. No group differences in time spent with novel or familiar objects were found. Thus, gonadectomy resulted in the emergence of significantly different responses to social stimuli, but not non-social stimuli. Our work suggests that intact gonads, which are needed to produce adolescent increases in circulating testosterone, impact social behavior during adolescences in primates.     

Changes in the chemistry and biota of Lake Carey: a large salt lake impacted by hypersaline discharge from mining operations in Western Australia

The environment of Lake Carey, a large salt lake in the goldfields of Western Australia, has been subjected to mining for the past 100 years. The effect of discharge of hypersaline water to the playa as a result of pit dewatering has been a grave concern. The aim of this paper was to investigate the influences of seasonal parameters and mining activity on the physico-chemical and biological attributes of Lake Carey. Assessment of water and sediment chemistry and benthic microbial communities (BMCs) has been carried out opportunistically since 1999, with particular emphasis on the differences between sites receiving dewatering discharge currently or in the past (Impacted Sites), and those which have never received dewatering discharge (Control Sites). Results of water and sediment analyses indicated that the impacts of dewatering discharge on Lake Carey were localised and evident in the vicinity of the discharge sites. However, large rainfall events, such as the cyclonic rainfall in 2004, could result in flushing and amelioration of sediments. This was also reflected in the sites which were historically impacted by dewatering discharge. The sites directly impacted by dewatering discharge displayed poor abundance and species richness of diatoms compared to the sites unaffected by dewatering discharge. However, recovery of these sites in terms of species richness and abundance is also initiated by large rainfall events, as shown by data collected from the historical dewatering discharge sites. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for Salt Lake Research     

Betaine administration corrects ethanol-induced defective VLDL secretion

Our previous studies, demonstrating ethanol-induced alterations in phosphatidylcholine (PC) synthesis via the phosphatidylethanolamine methyltransferase (PEMT) pathway, implicated a defect in very low-density lipoprotein (VLDL) secretion in the pathogenesis of hepatic steatosis. The objective of this study was to determine whether VLDL secretion was reduced by chronic ethanol consumption and whether betaine supplementation, that restores PEMT activity and prevents the development of alcoholic steatosis, could normalize VLDL secretion. The VLDL secretion in rats fed with control, ethanol and the betaine supplemented diets was determined using Triton WR-1339 to inhibit plasma VLDL metabolism. We observed reduced VLDL production rates in chronic alcohol-fed rats compared to control animals. Supplementation of betaine in the ethanol diet increased VLDL production rate to values significantly higher than those observed in the control diet-fed rats. To conclude, chronic ethanol consumption impairs PC generation via the PEMT pathway resulting in diminished VLDL secretion which contributes to the development of hepatic steatosis. By increasing PEMT-mediated PC generation, betaine results in increased fat export from the liver and attenuates the development of alcoholic fatty liver.     

Characterization of temperature dependent and substrate-binding cleft movements in Bacillus circulans family 11 xylanase: A molecular dynamics investigation

Background

Xylanases (EC 3.2.1.8) hydrolyze xylan, one of the most abundant plant polysaccharides found in nature, and have many potential applications in biotechnology.

Methods

Molecular dynamics simulations were used to investigate the effects of temperature between 298 to 338 K and xylobiose binding on residues located in the substrate-binding cleft of the family 11 xylanase from Bacillus circulans (BcX).

Results

In the absence of xylobiose the BcX exhibits temperature dependent movement of the thumb region which adopts an open conformation exposing the active site at the optimum catalytic temperature (328 K). In the presence of substrate, the thumb region restricts access to the active site at all temperatures, and this conformation is maintained by substrate/protein hydrogen bonds involving active site residues, including hydrogen bonds between Tyr69 and the 2′ hydroxyl group of the substrate. Substrate access to the active site is regulated by temperature dependent motions that are restricted to the thumb region, and the BcX/substrate complex is stabilized by extensive intermolecular hydrogen bonding with residues in the active site.

General significance

These results call for a revision of both the “hinge-bending” model for the activity of group 11 xylanases, and the role of Tyr69 in the catalytic mechanism.