Allosteric Activation of PI3Kα Results in Dynamic Access to Catalytically Competent Conformations

Class I phosphoinositide-3-kinases (PI3Ks) phosphorylate PIP₂ at its 3' inositol position to generate PIP₃, a second messenger that influences signaling cascades regulating cellular growth, survival, and proliferation. Previous studies have suggested that PI3Kα activation involves dislodging the p85α nSH2 domain from the p110α catalytic subunit by binding activated receptor tyrosine kinases. We carried out molecular dynamics simulations to determine, mechanistically and structurally, how PI3Kα conformations are influenced by physiological effectors and the nSH2 domain. We demonstrate that changes in protein dynamics mediated by allosteric regulation significantly increase the population of catalytically competent states without changing the enzyme ground-state structure. Furthermore, we demonstrate that modulation of active-site residue interactions with enzyme substrates can reciprocally influence nSH2 domain dynamics. Together, these results suggest that dynamic allostery plays a role in populating the catalytically competent conformation of PI3Kα, and provide a key platform for the design of novel chemotherapeutic PI3Kα inhibitors.

Northward range expansion in spring-staging barnacle geese is a response to climate change and population growth, mediated by individual experience

All long-distance migrants must cope with changing environments, but species differ greatly in how they do so. In some species, individuals might be able to adjust by learning from individual experiences and by copying others. This could greatly speed up the process of adjustment, but evidence from the wild is scarce. Here, we investigated the processes by which a rapidly growing population of barnacle geese (Branta leucopsis) responded to strong environmental changes on spring-staging areas in Norway. One area, Helgeland, has been the traditional site. Since the mid-1990s, an increasing number of geese stage in another area 250 km further north, Vesterålen. We collected data on goose numbers and weather conditions from 1975 to 2017 to explore the extent to which the increase in population size and a warmer climate contributed to this change in staging area use. During the study period, the estimated onset of grass growth advanced on average by 0.54 days/year in each of the two areas. The total production of digestible biomass for barnacle geese during the staging period increased in Vesterålen but remained stable in Helgeland. The goose population has doubled in size during the past 25 years, with most of the growth being accommodated in Vesterålen. The observations suggest that this dramatic increase would not have happened without higher temperatures in Vesterålen. Records of individually marked geese indicate that from the initial years of colonization onwards, especially young geese tended to switch to Vesterålen, thereby predominating in the flocks at Vesterålen. Older birds had a lower probability of switching to Vesterålen, but over the years, the probability increased for all ages. Our findings suggest that barnacle geese integrate socially learned behaviour with adjustments to individual experiences, allowing the population to respond rapidly and accurately to global change.

[Quantitative assessment of urban ecosystem services flow based on entropy theory: A case study of Beijing, China]

Quantitative evaluation of ecosystem service is a primary premise for rational resources exploitation and sustainable development. Examining ecosystem services flow provides a scientific method to quantity ecosystem services. We built an assessment indicator system based on land cover/land use under the framework of four types of ecosystem services. The types of ecosystem services flow were reclassified. Using entropy theory, disorder degree and developing trend of indicators and urban ecosystem were quantitatively assessed. Beijing was chosen as the study area, and twenty-four indicators were selected for evaluation. The results showed that the entropy value of Beijing urban ecosystem during 2004 to 2015 was 0.794 and the entropy flow was -0.024, suggesting a large disordered degree and near verge of non-health. The system got maximum values for three times, while the mean annual variation of the system entropy value increased gradually in three periods, indicating that human activities had negative effects on urban ecosystem. Entropy flow reached minimum value in 2007, implying the environmental quality was the best in 2007. The determination coefficient for the fitting function of total permanent population in Beijing and urban ecosystem entropy flow was 0.921, indicating that urban ecosystem health was highly correlated with total permanent population.

Humic Fertilizer and Vermicompost Applied to the Soil Can Positively Affect Population Growth Parameters of Trichogramma brassicae (Hymenoptera: Trichogrammatidae) on Eggs of Tuta absoluta (Lepidoptera: Gelechiidae)

The tomato leaf miner, Tuta absoluta (Meyrick), is a devastating pest of tomato worldwide. One of the control measures of T. absoluta is the use of biological control agents, such as Trichogramma wasps. Interactions between natural enemies and insect pests may be affected by application of fertilizers, because changes in plant quality through the fertilizer application may therefore affect herbivore characteristics and suitability of them to parasitism. Laboratory tests were carried out to evaluate the life table parameters of Trichogramma brassicae Bezdenko on T. absoluta eggs reared on tomato plants treated either with vermicompost (40%), humic fertilizer (2 g/kg soil), or control (suitable mixture of field soil and sand). Population growth parameters of T. brassicae were affected by fertilizer treatments. Significant differences were found for immature life period and total fecundity of T. brassicae on the treatments. Differences of intrinsic rate of natural increase (r _m), finite rate of increase (λ), net reproductive rate (R ₀), mean generation time (T), and doubling time (DT) of T. brassicae among treatments were also significant. The lowest values of r _m, λ, and R ₀ were recorded for T. brassicae developed on T. absoluta eggs on control treatment, whereas the highest values of these parameters were observed on 2 g/kg humic fertilizer. Furthermore, T. brassicae had the shortest T and DT values on 2 g/kg humic fertilizer and 40% vermicompost treatments. Our results showed that application of humic fertilizer and vermicompost could positively affect population growth parameters of T. brassicae on eggs of T. absoluta fed on tomato plants.

Migrations and Multiplications of Bursaphelenchus xylophilus and B. mucronatus in Pinus thumbergii in Relation to Their Pathogenicity

To evaluate the mechanisms of pathogenicity and non-pathogenicity of Bursaphelenchus xylophilus and B. mucronatus isolated in South Korea, we used 4-year-old P. thunbergii seedlings and 20-cm long one-year-old stem cuttings of 5-year-old Pinus thunbergii, and studied distributions and multiplications of pine wood nematodes after inoculation. The distributions of B. xylophilus in the 20-cm pine stem cuttings were not significantly different from that of B. mucronatus. Conversely, the proliferation rate of B. xylophilus on mycelial mats of Botrytis cinerea was significantly different from that of B. mucronatus. The study using 4-year-old P. thunbergii seedlings also showed that B. mucronatus can migrate to distal portions of the pine seedlings the same as B. xylophilus, but the populations of B. xylophilus remaining in the pine seedlings were relatively larger than those of B. mucronatus. Therefore, we concluded that the pathogenicity of B. xylophilus could be strongly influenced by its ability to multiply.

Climate change and population growth in Timor Leste: implications for food security

The climate in Timor Leste (East Timor) is predicted to become about 1.5 °C warmer and about 10 % wetter on average by 2050. By the same year, the population is expected to triple from 1 to 2.5-3 million. This article maps the predicted changes in temperature and rainfall and reviews the implications of climate change and population growth on agricultural systems. Improved cultivars of maize, rice, cassava, sweet potato and peanuts with high yield performance have been introduced, but these will need to be augmented in the future with better adapted cultivars and new crops, such as food and fodder legumes and new management practices. The requirements for fertilizers to boost yields and terracing and/or contour hedgerows to prevent soil erosion of steeply sloping terrain are discussed. Contour hedges can also be used for fodder for improved animal production to provide protein to reduce malnutrition.

Population Dynamics of Belonolaimus longicaudatusin a Cotton Production System

Belonolaimus longicaudatus is a recognized pathogen of cotton (Gossypium hirsutum), but insufficient information is available on the population dynamics and economic thresholds of B. longicaudatus in cotton production. In this study, data collected from a field in Florida were used to develop models predicting population increases of B. longicaudatus on cotton and population declines under clean fallow. Population densities of B. longicaudatus increased on cotton, reaching a carrying capacity of 139 nematodes/130 cm(3) of soil, but decreased exponentially during periods of bare fallow. The model indicated that population densities should decrease each year of monocropped cotton, if an alternate host is not present between sequential cotton crops. Economic thresholds derived from published damage functions and current prices for cotton and nematicides varied from 2 to 5 B. longicaudatus/130 cm(3) of soil, depending on the nematicide used.

Degree-day Models for Predicting Egg Hatch and Population Increase of Criconemella xenoplax

A degree-day model was derived to predict egg hatch for Criconemella xenoplax. Eggs collected from gravid females were incubated in distilled water at constant temperatures of 10-35 C. Sixty-six percent of all eggs hatched between 13 and 32 C, and 42% hatched at 10 C. All eggs aborted above 32.5 C. Between 25 and 32 C, 8.5 +/- 0.5 days were required for egg hatch. Degree-day requirement for egg hatch at 10-30 C was estimated to be 154 +/- 5 with a base of 9.03 +/- 0.04 C. This base of 9 C was adopted in studies of the relationship between degree-days and nematode population increase on Prunus seedlings grown 9-11 weeks in a greenhouse. Degree-day accumulations were based upon daily averages from maximum and minimum air temperatures. Ratios of final to initial population densities exhibited an exponential pattern in relation to degree-day accumulations with proportionate doubling increment of 0.100 +/- 0.049 every 139 +/- 8 degree-days. These results provide a means of predicting nematode population increase under greenhouse conditions and a basis for choosing sampling intervals when evaluating nematode multiplication.

Evaluation of Host Suitability in Prunus for Criconemella xenoplax

Methods were developed for screening Prunus selections for host suitability to Criconemella xenoplax. The relative host suitability of selections was based upon a doubling accumulation value (beta) that was defined as the number of degree-days (base 9 C) required for doubling of an increment of the initial nematode population. The beta value characteristic for C. xenoplax (139 +/- 8 degree-days) on suitable hosts was similar to the average beta value determined for several peach rootstocks known to be suitable hosts. The beta values were 144 +/- 21 for Halford, 141 +/- 16 for Lovell, and 138 +/- 10 for Nemaguard. A higher value for beta could indicate poorer host suitability or resistance of a selection to C. xenoplax. All of 369 Prunus accessions tested, including eight accessions that had survived well on a field site infested with C. xenoplax, were suitable hosts. Apparently, resistance to C. xenoplax was not a factor in survival of the accessions planted in the field. Seedlings from P. besseyi, P. pumila 'Mando', and two interspecific hybrids, Redcoat and Sapalta IR 549-1, failed to support nematode population increase in 44-81% of tests conducted, but all selections supported population increase in some tests. These accessions may have resistance mechanisms that are active only under specific conditions.

Races of the Barley Root-Knot Nematode, Meloidogyne naasi. III. Reproduction and Pathogenicity on Creeping Bentgrass

Reproduction and pathogenicity of the five known races of Meloidogyne naasi on two selections of creeping bentgrass were compared. Toronto C-15 was a host for Races 3, 4 and 5, whereas Northmoor 9 supported reproduction of all five races. Differences in susceptibility and population increase demonstrated that the races could be separated by degree of reproduction on the two selections. Root weights generally were unaffected. Based on cumulative dipping weights, all but Race 1 were pathogenic on at least one of the selections; Race 3 stunted top growth of both. Slight differences in degree of pathogenicity, associated with final populations, were not broad enough to be useful in race separation.