N-Acyl Homoserine Lactones in Diverse Pectobacterium and Dickeya Plant Pathogens: Diversity, Abundance, and Involvement in Virulence

Soft-rot bacteria Pectobacterium and Dickeya use N-acyl homoserine lactones (NAHSLs) as diffusible signals for coordinating quorum sensing communication. The production of NAHSLs was investigated in a set of reference strains and recently-collected isolates, which belong to six species and share the ability to infect the potato host plant. All the pathogens produced different NAHSLs, among which the 3-oxo-hexanoyl- and the 3-oxo-octanoyl-l-homoserine lactones represent at least 90% of total produced NAHSL-amounts. The level of NAHSLs varied from 0.6 to 2 pg/cfu. The involvement of NAHSLs in tuber maceration was investigated by electroporating a quorum quenching vector in each of the bacterial pathogen strains. All the NAHSL-lactonase expressing strains produced a lower amount of NAHSLs as compared to those harboring the empty vector. Moreover, all except Dickeya dadantii 3937 induced a lower level of symptoms in potato tuber assay. Noticeably, aggressiveness appeared to be independent of both nature and amount of produced signals. This work highlights that quorum sensing similarly contributed to virulence in most of the tested Pectobacterium and Dickeya, even the strains had been isolated recently or during the past decades. Thus, these key regulatory-molecules appear as credible targets for developing anti-virulence strategies against these plant pathogens

Zoledronic acid renders human M1 and M2 macrophages susceptible to Vδ2(+) γδ T cell cytotoxicity in a perforin-dependent manner.

Vδ2(+) T cells are a subpopulation of γδ T cells in humans that are cytotoxic towards cells which accumulate isopentenyl pyrophosphate. The nitrogen-containing bisphosphonate, zoledronic acid (ZA), can induce tumour cell lines to accumulate isopentenyl pyrophosphate, thus rendering them more susceptible to Vδ2(+) T cell cytotoxicity. However, little is known about whether ZA renders other, non-malignant cell types susceptible. In this study we focussed on macrophages (Mϕs), as these cells have been shown to take up ZA. We differentiated peripheral blood monocytes from healthy donors into Mϕs and then treated them with IFN-γ or IL-4 to generate M1 and M2 Mϕs, respectively. We characterised these Mϕs based on their phenotype and cytokine production and then tested whether ZA rendered them susceptible to Vδ2(+) T cell cytotoxicity. Consistent with the literature, IFN-γ-treated Mϕs expressed higher levels of the M1 markers CD64 and IL-12p70, whereas IL-4-treated Mϕs expressed higher levels of the M2 markers CD206 and chemokine (C-C motif) ligand 18. When treated with ZA, both M1 and M2 Mϕs became susceptible to Vδ2(+) T cell cytotoxicity. Vδ2(+) T cells expressed perforin and degranulated in response to ZA-treated Mϕs as shown by mobilisation of CD107a and CD107b to the cell surface. Furthermore, cytotoxicity towards ZA-treated Mϕs was sensitive-at least in part-to the perforin inhibitor concanamycin A. These findings suggest that ZA can render M1 and M2 Mϕs susceptible to Vδ2(+) T cell cytotoxicity in a perforin-dependent manner, which has important implications regarding the use of ZA in cancer immunotherapy

The First Post-Kepler Brightness Dips of KIC 8462852

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <<1um, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term "secular" dimming, which may be caused by independent processes, or probe different regimes of a single process

Extrasolar enigmas: from disintegrating exoplanets to exoasteroids

Thousands of transiting exoplanets have been discovered to date, thanks in great part to the {\em Kepler} space mission. As in all populations, and certainly in the case of exoplanets, one finds unique objects with distinct characteristics. Here we will describe the properties and behaviour of a small group of `disintegrating' exoplanets discovered over the last few years (KIC 12557548b, K2-22b, and others). They evaporate, lose mass unraveling their naked cores, produce spectacular dusty comet-like tails, and feature highly variable asymmetric transits. Apart from these exoplanets, there is observational evidence for even smaller `exo-'objects orbiting other stars: exoasteroids and exocomets. Most probably, such objects are also behind the mystery of Boyajian's star. Ongoing and upcoming space missions such as {\em TESS} and PLATO will hopefully discover more objects of this kind, and a new era of the exploration of small extrasolar systems bodies will be upon us.Comment: Accepted for publication in the book "Reviews in Frontiers of Modern Astrophysics: From Space Debris to Cosmology" (eds Kabath, Jones and Skarka; publisher Springer Nature) funded by the European Union Erasmus+ Strategic Partnership grant "Per Aspera Ad Astra Simul" 2017-1-CZ01-KA203-03556

Beyond equilibrium climate sensitivity

ISSN:1752-0908ISSN:1752-089

Death Don't Have No Mercy and Neither Does Calcium: Arabidopsis CYCLIC NUCLEOTIDE GATED CHANNEL2 and Innate Immunity

Plant innate immune response to pathogen infection includes an elegant signaling pathway leading to reactive oxygen species generation and resulting hypersensitive response (HR); localized programmed cell death in tissue surrounding the initial infection site limits pathogen spread. A veritable symphony of cytosolic signaling molecules (including Ca(2+), nitric oxide [NO], cyclic nucleotides, and calmodulin) have been suggested as early components of HR signaling. However, specific interactions among these cytosolic secondary messengers and their roles in the signal cascade are still unclear. Here, we report some aspects of how plants translate perception of a pathogen into a signal cascade leading to an innate immune response. We show that Arabidopsis thaliana CYCLIC NUCLEOTIDE GATED CHANNEL2 (CNGC2/DND1) conducts Ca(2+) into cells and provide a model linking this Ca(2+) current to downstream NO production. NO is a critical signaling molecule invoking plant innate immune response to pathogens. Plants without functional CNGC2 lack this cell membrane Ca(2+) current and do not display HR; providing the mutant with NO complements this phenotype. The bacterial pathogen–associated molecular pattern elicitor lipopolysaccharide activates a CNGC Ca(2+) current, which may be linked to NO generation due to buildup of cytosolic Ca(2+)/calmodulin

Death Don’t Have No Mercy and Neither Does Calcium:Arabidopsis cyclic nucleotide gated channel2 and Innate Immunity

Plant innate immune response to pathogen infection includes an elegant signaling pathway leading to reactive oxygen species generation and resulting hypersensitive response (HR); localized programmed cell death in tissue surrounding the initial infection site limits pathogen spread. A veritable symphony of cytosolic signaling molecules (including Ca2+, nitric oxide [NO], cyclic nucleotides, and calmodulin) have been suggested as early components of HR signaling. However, specific interactions among these cytosolic secondary messengers and their roles in the signal cascade are still unclear. Here, we report some aspects of how plants translate perception of a pathogen into a signal cascade leading to an innate immune response. We show that Arabidopsis thaliana CYCLIC NUCLEOTIDE GATED CHANNEL2 (CNGC2/DND1) conducts Ca2+ into cells and provide a model linking this Ca2+ current to downstream NO production. NO is a critical signaling molecule invoking plant innate immune response to pathogens. Plants without functional CNGC2 lack this cell membrane Ca2+ current and do not display HR; providing the mutant with NO complements this phenotype. The bacterial pathogen–associated molecular pattern elicitor lipopolysaccharide activates a CNGC Ca2+ current, which may be linked to NO generation due to buildup of cytosolic Ca2+/calmodulin