Non-Mendelian transmission of accessory chromosomes in fungi

Non-Mendelian transmission has been reported for various genetic elements, ranging from small transposons to entire chromosomes. One prime example of such a transmission pattern are B chromosomes in plants and animals. Accessory chromosomes in fungi are similar to B chromosomes in showing presence/absence polymorphism and being non-essential. How these chromosomes are transmitted during meiosis is however poorly understood-despite their often high impact on the fitness of the host. For several fungal organisms, a non-Mendelian transmission or a mechanistically unique meiotic drive of accessory chromosomes have been reported. In this review, we provide an overview of the possible mechanisms that can cause the non-Mendelian transmission or meiotic drives of fungal accessory chromosomes. We compare processes responsible for the non-Mendelian transmission of accessory chromosomes for different fungal eukaryotes and discuss the structural traits of fungal accessory chromosomes affecting their meiotic transmission. We conclude that research on fungal accessory chromosomes, due to their small size, ease of sequencing, and epigenetic profiling, can complement the study of B chromosomes in deciphering factors that influence and regulate the non-Mendelian transmission of entire chromosomes

Epigenetic modifications affect the rate of spontaneous mutations in a pathogenic fungus

Mutations are the source of genetic variation and the substrate for evolution. Genome-widemutation rates appear to be affected by selection and are probably adaptive. Mutation ratesare also known to vary along genomes, possibly in response to epigenetic modifications, butcausality is only assumed. In this study we determine the direct impact of epigenetic mod-ifications and temperature stress on mitotic mutation rates in a fungal pathogen using amutation accumulation approach. Deletion mutants lacking epigenetic modifications confirmthat histone mark H3K27me3 increases whereas H3K9me3 decreases the mutation rate.Furthermore, cytosine methylation in transposable elements (TE) increases the mutation rate15-fold resulting in significantly less TE mobilization. Also accessory chromosomes havesignificantly higher mutation rates. Finally, wefind that temperature stress substantiallyelevates the mutation rate. Taken together, wefind that epigenetic modifications andenvironmental conditions modify the rate and the location of spontaneous mutations in thegenome and alter its evolutionary trajectory

No anomalous supersaturation in ultracold cirrus laboratory experiments

High-altitude cirrus clouds are climatically important: their formation freeze-dries air ascending to the stratosphere to its final value, and their radiative impact is disproportionately large. However, their formation and growth are not fully understood, and multiple in situ aircraft campaigns have observed frequent and persistent apparent water vapor supersaturations of 5 %–25 % in ultracold cirrus (T<205 K), even in the presence of ice particles. A variety of explanations for these observations have been put forth, including that ultracold cirrus are dominated by metastable ice whose vapor pressure exceeds that of hexagonal ice. The 2013 IsoCloud campaign at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud and aerosol chamber allowed explicit testing of cirrus formation dynamics at these low temperatures. A series of 28 experiments allows robust estimation of the saturation vapor pressure over ice for temperatures between 189 and 235 K, with a variety of ice nucleating particles. Experiments are rapid enough (∼10 min) to allow detection of any metastable ice that may form, as the timescale for annealing to hexagonal ice is hours or longer over the whole experimental temperature range. We show that in all experiments, saturation vapor pressures are fully consistent with expected values for hexagonal ice and inconsistent with the highest values postulated for metastable ice, with no temperature-dependent deviations from expected saturation vapor pressure. If metastable ice forms in ultracold cirrus clouds, it appears to have a vapor pressure indistinguishable from that of hexagonal ice to within about 4.5 %

Boro-nitriding coating on pure iron by powder-pack boriding and nitriding processes

To alleviate spallation and crack difficulties exhibited by a borided metallic surface when it is subjected to a normal, heavy and sliding load under dry conditions, a boron nitride coating was produced on pure iron in two stages: boriding the iron surface at 950 °C for 6 h and then nitriding the pre-borided iron at 550 °C for 6 h. The powder-pack technique was used in both stages. XRD measurements confirmed that the grown layers were nitrides and duplex borides. The produced diffusion of the layers reached 240 µm in depth as measured by SEM images. The measured microhardness across the case favoured the interphase cohesion between the iron nitrides and iron borides layers. Consequently, the multicomponent coating exhibited superior wear resistance to an applied normal load under dry sliding contact conditions in comparison to borided iron

Snowmass 2021 White Paper: Cosmogenic Dark Matter and Exotic Particle Searches in Neutrino Experiments

The signals from outer space and their detection have been playing animportant role in particle physics, especially in discoveries of and searchesfor physics beyond the Standard Model (BSM); beyond the evidence of dark matter(DM), for example, the neutrinos produced from the dark matter annihilation isimportant for the indirect DM searches. Moreover, a wide range of new,well-motivated physics models and dark-sector scenarios have been proposed inthe last decade, predicting cosmogenic signals complementary to those in theconventional direct detection of particle-like dark matter. Most notably,various mechanisms to produce (semi-)relativistic DM particles in the presentuniverse (e.g. boosted dark matter) have been put forward, while beingconsistent with current observational and experimental constraints on DM. Theresulting signals often have less intense and more energetic fluxes, to whichunderground, kiloton-scale neutrino detectors can be readily sensitive. Inaddition, the scattering of slow-moving DM can give rise to a sizable energydeposit if the underlying dark-sector model allows for a large mass differencebetween the initial and final state particles, and the neutrino experimentswith large volume detectors are well suited for exploring these opportunities. This White Paper is devoted to discussing the scientific importance of thecosmogenic dark matter and exotic particle searches, not only overviewing therecent efforts in both the theory and the experiment communities but alsoproviding future perspectives and directions on this research branch. Alandscape of technologies used in neutrino detectors and their complementarityis discussed, and the current and developing analysis strategies are outlined.<br