Impact of Thermal Stress on the Moroccan Argan Agroecosystem

The argan tree is exclusively endemic in the drylands of Southwest Morocco, an agroecosystem of great ecological, cultural, and economic importance. The argan agroecosystem is already damaged. It is particularly vulnerable to climate change as well as the harsh natural conditions aggravated by the current population growth and the exploitation in excess of the production capacities. Unfortunately, during the 20th century, its area has been reduced by half. Current projections indicate an increase in temperature under climate scenarios. Anticipated climate change could accelerate this trend resulting in the argan tree degradation. To assess the climate change impact, the authors used the SDSM model at the argan agroecosystem scale and the thermal stress model to assess its vulnerability and estimate its tolerance response in relation to temperature stress for a projected climate in the near term (2010-2025 years). In this chapter, the authors explored the impact of climate change on the argan tree regeneration.

Drug tolerance facilitates the evolution of drug resistance in Candida albicans

Background For Candida albicans and Candidiasis, drug resistance is sometimes due to the pre-existence of genetic polymorphisms that bypass the mode of action of the drug, thus conferring a long-term survival benefit. In other cases, resistance is acquired via the evolution of de novo genetic polymorphisms. There is evidence that C. albicans possess a drug tolerance response which “buys time” for individuals to evolve beneficial mutations. Our goal here is to characterize this poorly understood epigenetic cytoprotective program at the single cell molecular level. Methods We developed a nano-litre droplet based Candida single cell sequencing platform capable of transcriptionally profiling several thousand individual cells in an efficient manner. We exploit this platform to profile both untreated and drug exposed (incl. fluconazole, caspofungin and nystatin) populations at early time points post-treatment (tolerance) and late time points (resistance) in order to understand survival trajectories. The profile are compared with the matched sequenced genomes. Results We show that untreated Candida populations exhibit “bet hedging”, stochastically expressing cytoprotective transcriptional programs, and drug tolerant individuals partition into distinct subpopulations, each with a unique survival strategy involving different transcriptional programs. We observe a burst of chromosomal aberrations at two days post-treatment that differ between survivor subpopulation. Discussion Our single cell approach highlights that survivor subpopulations pass through a tolerance phase that involves a multivariate transcriptional response including upregulation of efflux pumps, chaperones and transport mechanisms, and cell wall maintenance. Together this suggests that targeting the tolerance response concomitantly with standard therapies could represent an efficient approach to ablating clinical persistence.

Retromer Complex and PI3K Complex II-Related Genes Mediate the Yeast (Saccharomyces cerevisiae) Sodium Metabisulfite Resistance Response

Sodium metabisulfite (Na2S2O5) is widely used as a preservative in the food and wine industry. However, it causes varying degrees of cellular damage to organisms. In order to improve our knowledge regarding its cyto-toxicity, a genome-wide screen using the yeast single deletion collection was performed. Additionally, a total of 162 Na2S2O5-sensitive strains and 16 Na2S2O5-tolerant strains were identified. Among the 162 Na2S2O5 tolerance-related genes, the retromer complex was the top enriched cellular component. Further analysis demonstrated that retromer complex deletion leads to increased sensitivity to Na2S2O5, and that Na2S2O5 can induce mislocalization of retromer complex proteins. Notably, phosphatidylinositol 3-monophosphate kinase (PI3K) complex II, which is important for retromer recruitment to the endosome, might be a potential regulator mediating retromer localization and the yeast Na2S2O5 tolerance response. Na2S2O5 can decrease the protein expressions of Vps34, which is the component of PI3K complex. Therefore, Na2S2O5-mediated retromer redistribution might be caused by the effects of decreased Vps34 expression levels. Moreover, both pharmaceutical inhibition of Vps34 functions and deletions of PI3K complex II-related genes affect cell tolerance to Na2S2O5. The results of our study provide a global picture of cellular components required for Na2S2O5 tolerance and advance our understanding concerning Na2S2O5-induced cytotoxicity effects.

Predicting selection-response gradients of heat tolerance in a wide-ranging reef-building coral

ABSTRACTOcean temperatures continue to rise due to climate change but it is unclear if heat tolerance of marine organisms will keep pace. Understanding how tolerance scales from individuals to species and quantifying adaptive potentials is essential to forecasting responses to warming. We reproductively crossed corals from a globally distributed species (Acropora tenuis) on the Great Barrier Reef (Australia) from three thermally distinct reefs to create 85 novel offspring lineages. Individuals were experimentally exposed to temperatures (27.5, 31, and 35.5 - 36 °C) in adult and two critical early life-history stages (larval development and settlement) to assess acquired heat tolerance via introgression on offspring phenotypes by comparing multiple physiological responses (photosynthetic yields, bleaching, necrosis, settlement, and survival). Adaptive potentials and physiological reaction norms were calculated across multiple life-stages to integrate heat tolerance at different biological scales. Selective breeding improved larval survival to heat by 1.5-2.5x but settlement success showed limited improvement. Adult responses to selection at heat were similar but were greater in larvae from warmer reefs compared to the cooler reef. There was also a divergence between adults and offspring mean population responses, likely underpinned by heat stress imposing strong divergent selection on adult colonies. These results have implications for downstream selection during reproduction, as evidenced by variability in a conserved heat tolerance response across offspring lineages. These results inform our ability to forecast the impacts of climate change on wild populations of corals and will aid in developing novel conservation tools like the assisted evolution of at-risk species.SUMMARY STATEMENTHeat stress exerts disruptive selection on adult corals. This likely underpins variability in offspring survival and results in differences in offspring responses to selection.

Pyruvate oxidase as a key determinant of pneumococcal viability during transcytosis across brain endothelium.

Streptococcus pneumoniae (SPN/pneumococcus), invades myriad of host tissues following efficient breaching of cellular barriers. However, strategies adopted by pneumococcus for evasion of host intracellular defences governing successful transcytosis across host cellular barriers remain elusive. In this study, using brain endothelium as a model host barrier, we observed that pneumococcus containing endocytic vacuoles (PCVs) formed following SPN internalization into brain microvascular endothelial cells (BMECs), undergo early maturation and acidification, with a major subset acquiring lysosome-like characteristics. Exploration of measures that would preserve pneumococcal viability in the lethal acidic pH of these lysosome-like vacuoles revealed a critical role of the two-component system response regulator, CiaR, which has been previously implicated in induction of acid tolerance response. Pyruvate oxidase (SpxB), a key sugar metabolizing enzyme that catalyses oxidative decarboxylation of pyruvate to acetyl phosphate, was found to contribute to acid stress tolerance, presumably via acetyl phosphate-mediated phosphorylation and activation of CiaR, independent of its cognate kinase CiaH. Hydrogen peroxide, the by-product of SpxB catalysed reaction, was also found to improve pneumococcal intracellular survival by oxidative inactivation of lysosomal cysteine cathepsins, thus compromising the degradative capacity of the host lysosomes. Expectedly, a Δ spxB mutant was found to be significantly attenuated in its ability to survive inside the BMEC endocytic vacuoles, reflecting in its reduced transcytosis ability. Collectively, our studies establish SpxB as an important virulence determinant facilitating pneumococcal survival inside host cells, ensuring successful trafficking across host cellular barriers. IMPORTANCE Host cellular barriers have innate immune defences to restrict microbial passage into sterile compartments. Here, by focussing on the blood-brain barrier endothelium, we investigated mechanisms which enable Streptococcus pneumoniae to traverse through host barriers. Pyruvate oxidase, a pneumococcal sugar metabolizing enzyme was found to play a crucial role in this, via generation of acetyl phosphate and hydrogen peroxide. A two-pronged approach consisting of acetyl phosphate-mediated activation of acid tolerance response and hydrogen peroxide-mediated inactivation of lysosomal enzymes enabled pneumococci to maintain viability inside the degradative vacuoles of the brain endothelium, for successful transcytosis across the barrier. Thus, pyruvate oxidase is a key virulence determinant and can potentially serve as a viable candidate for therapeutic interventions for better management of invasive pneumococcal diseases.