Plant nitrate supply regulates Erwinia amylovora virulence gene expression in Arabidopsis

We showed previously that nitrogen (N) limitation decreases Arabidopsis resistance to Erwinia amylovora (Ea). We show that decreased resistance to bacteria in low N is correlated with lower apoplastic reactive oxygen species (ROS) accumulation and lower jasmonic acid (JA) pathway expression. Consistently, pretreatment with methyl jasmonate (Me-JA) increased the resistance of plants grown under low N. In parallel, we show that in planta titres of a nonvirulent type III secretion system (T3SS)-deficient Ea mutant were lower than those of wildtype Ea in low N, as expected, but surprisingly not in high N. This lack of difference in high N was consistent with the low expression of the T3SS-encoding hrp virulence genes by wildtype Ea in plants grown in high N compared to plants grown in low N. This suggests that expressing its virulence factors in planta could be a major limiting factor for Ea in the nonhost Arabidopsis. To test this hypothesis, we preincubated Ea in an inducing medium that triggers expression of hrp genes in vitro, prior to inoculation. This preincubation strongly enhanced Ea titres in planta, independently of the plant N status, and was correlated to a significant repression of JA-dependent genes. Finally, we identify two clusters of metabolites associated with resistance or with susceptibility to Ea. Altogether, our data showed that high susceptibility of Arabidopsis to Ea, under low N or following preincubation in hrp-inducing medium, is correlated with high expression of the Ea hrp genes in planta and low expression of the JA signalling pathway, and is correlated with the accumulation of specific metabolites.     

Amino Acid Substitutions That Affect Receptor Binding and Stability of the Hemagglutinin of Influenza A/H7N9 Virus

Receptor-binding preference and stability of hemagglutinin have been implicated as crucial determinants of airborne transmission of influenza viruses. Here, amino acid substitutions previously identified to affect these traits were tested in the context of an A/H7N9 virus. Some combinations of substitutions, most notably G219S and K58I, resulted in relatively high affinity for α2,6-linked sialic acid receptor and acid and temperature stability. Thus, the hemagglutinin of the A/H7N9 virus may adopt traits associated with airborne transmission.     

Warmer winters result in reshaping of the European beech forest soil microbiome (bacteria,archaea and fungi)—With potential implications for ecosystem functioning

In temperate regions, climate warming alters temperature and precipitation regimes. During winter, a decline in insulating snow cover changes the soil environment, where especially frost exposure can have severe implications for soil microorganisms and subsequently for soil nutrient dynamics. Here, we investigated winter climate change responses in European beech forests soil microbiome. Nine study sites with each three treatments (snow exclusion, insolation, and ambient) were investigated. Long-term adaptation to average climate was explored by comparing across sites. Triplicated treatment plots were used to evaluate short-term (one single winter) responses. Community profiles of bacteria, archaea and fungi were created using amplicon sequencing. Correlations between the microbiome, vegetation and soil physicochemical properties were found. We identify core members of the forest-microbiome and link them to key processes, for example, mycorrhizal symbiont and specialized beech wood degraders (fungi) and nitrogen cycling (bacteria, archaea). For bacteria, the shift of the microbiome composition due to short-term soil temperature manipulations in winter was similar to the community differences observed between long-term relatively cold to warm conditions. The results suggest a strong link between the changes in the microbiomes and changes in environmental processes, for example, nitrogen dynamics, driven by variations in winter climate.     

Climate-driven range dynamics of the freshwater limpet, Ancylus fluviatilis (Pulmonata, Basommatophora)

Aim Our aim was to understand the processes that have shaped the present‐day distribution of the freshwater limpet Ancylus fluviatilis sensu stricto in order to predict the consequences of global climate change for the geographical range of this species. Location North‐western Europe. Methods We sampled populations of A. fluviatilis sensu stricto over the entire range of the species (north‐western Europe) and sequenced 16S ribosomal RNA (16S) and cytochrome oxidase subunit I (COI) mitochondrial fragments to perform phylogenetic and phylogeographical analyses. Climatic niche modelling allowed us to infer the climatic preferences of the species. A principal components analysis identified the most important climatic factors explaining the actual range of A. fluviatilis. We also identified which climatic factor was the most limiting at range margins, and predicted the species’ geographical range under a climate change scenario [Community Climate Model 3 (CCM3)]. Results By means of the phylogeographical analysis, we infer that A. fluviatilis sensu stricto occupied northern refuges during the Last Glacial Maximum. We show that the climatic preferences of Baltic populations are significantly different from those of Central European populations. The projection of the occupied area under the CCM3 climate model predicts a moderate poleward shift of the northern range limits, but a dramatic loss of areas currently occupied, for instance in northern Germany and in southern Great Britain. Main conclusions The post‐glacial range dynamics of A. fluviatilis are not governed by niche conservatism. Therefore, we must be cautious about bioclimatic model predictions: the expected impact of climate change could be tempered by the adaptive potential this species has already shown in its evolutionary history. Thus, modelling approaches should rather be seen as conservative forecasts of altered species ranges as long as the adaptive potential of the organisms in question cannot be predicted.     

Hairpins under tension: RNA versus DNA

We use optical tweezers to control the folding and unfolding of individual DNA and RNA hairpins by force. Four hairpin molecules are studied in comparison: two DNA and two RNA ones. We observe that the conformational dynamics is slower for the RNA hairpins than for their DNA counterparts. Our results indicate that structures made of RNA are dynamically more stable. This difference might contribute to the fact that DNA and RNA play fundamentally different biological roles in spite of chemical similarity.     

Inhibition of ornithine decarboxylase in human fibroblast cells by type I and type II interferons

Dilution of human fibroblast GM2767 cell cultures into fresh serum-containing growth medium induces ornithine decarboxylase activity 45-fold over a six-hour interval. When the fibroblast cultures are supplemented with human fibroblast α-, β-, or γ-interferon at the time of dilution into fresh growth medium, the induction of ornithine decarboxylase is inhibited 61%, 90%, and 65%, respectively. β-Interferon is the most effective type of interferon to inhibit induction of ornithine decarboxylase.     

Robustness of epithelial sealing is an emerging property of local ERK feedback driven by cell elimination

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Performance of Ooencyrtus kuvanae (Hymenoptera: Encyrtidae) on two host species,Halyomorpha halys and Philosamia ricini

The brown marmorated stink bug, Halyomorpha halys, is an invasive agricultural pest of fruit trees and vegetables. Egg parasitoids play a key role in the reducing of H. halys populations. Ooencyrtus kuvanae (Howard) (Hymenoptera: Encyrtidae) can parasitize H. halys and complete its life cycle in this host species. Many factors can influence this parasitoid–host relationship. Of these factors, we evaluated the effect of female age, exposure time, and host species on the biological characteristics and fecundity of O. kuvanae reared on eggs of H. halys as well as another previously known host Philosamia ricini (Lepidoptera: Saturniidae). In this study, we used a 3-year-old laboratory colony of O. kuvanae. Parasitism rates positively affected by exposure time in P. ricini. The highest parasitism rates were obtained in 5- and 7-day-old females of both hosts. The highest emergence rates were recorded on P. ricini for 5- and 7-day-old female P. ricini (81.8% and 84.8%, respectively). The development time of O. kuvanae ranged from 18.4 to 19.1 days on H. halys and 17.7 to 18.3 days on P. ricini. The longevity of O. kuvanae that were provided honey was 38.5 and 47.8 days on H. halys and P. ricini, respectively. The longevity of O. kuvanae that were not provided honey was 2.3 and 2.8 days on H. halys and P. ricini, respectively. The sex ratio was male-biased (36.5% female) on H. halys and female-biased (55.2% female) on P. ricini. Fecundity of O. kuvanae was 37.7 and 59.6 progeny per female for H. halys and P. ricini, respectively. The performance of O. kuvanae was lower when compared with its performance on the host P. ricini. Our results suggest that O. kuvanae has potential as new biological control agent for H. halys.     

Die Organisation des optischen Feldes bei der Biene. II

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