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Fluid inclusions in mineralized fracture infillings (i.e., veins) could preserve information about subsurface fluids like temperature and salinity. The isotopic composition of water in these fluid inclusions could provide direct evidence of the provenance of these mineral‐forming fluids. So far, the isotope compositions of fluid inclusions have been mainly derived from carbonate veins and other precipitates, like speleothems. The aim of this study is to analyse the δ18O and δ2H isotopic compositions of aqueous fluid inclusions of quartz veins using a cavity ring‐down spectroscopy (CRDS) analyser in combination with a moisturized nitrogen background and mechanical crusher. For this study, we analysed δ18O and δ2H values of fluid inclusions in quartz veins from three north‐western European locations formed during the Variscan orogeny. Prior to crushing, the fluid‐rich quartz fraction was separated from the pure quartz fraction, from other mineral phases and host rock by using conventional heavy liquids and magnet separation. Raman spectrometry detected some rare occurrences of hydrocarbon, methane, and nitrogen in the fluid inclusions. The samples were sequentially crushed to elucidate the potential impact of different fluid inclusion assemblages (FIA) on the δ18O and δ2H values. The results from single and sequential mechanical crushing, together with interlaboratory comparisons, exhibit reliable and consistent isotopic patterns across locations with high precision (for δ18O: 1σ SD < 0.8‰; for δ2H: 1σ SD < 1.5‰). The obtained data occur in three different clusters for three study zones, providing evidence for the presence of meteoric‐derived fluids in the fold‐and‐thrust belts of the Variscan orogeny. These findings demonstrate that the CRDS approach can be successfully applied to quartz minerals, investigating fluid pathways within the upper crust and the formation of these secondary minerals. [ABSTRACT FROM AUTHOR]

Background: Root-knot nematodes transform vascular host cells into permanent feeding structures to withdraw nutrients from the host plant. Ecotypes of Arabidopsis thaliana can display large quantitative variation in susceptibility to the root-knot nematode Meloidogyne incognita, which is thought to be independent of dominant major resistance genes. However, in an earlier genome-wide association study of the interaction between Arabidopsis and M. incognita we identified a quantitative trait locus harboring homologs of dominant resistance genes but with minor effect on susceptibility to the M. incognita population tested., Results: Here, we report on the characterization of two of these genes encoding the TIR-NB-LRR immune receptor DSC1 (DOMINANT SUPPRESSOR OF Camta 3 NUMBER 1) and the TIR-NB-LRR-WRKY-MAPx protein WRKY19 in nematode-infected Arabidopsis roots. Nematode infection studies and whole transcriptome analyses using the Arabidopsis mutants showed that DSC1 and WRKY19 co-regulate susceptibility of Arabidopsis to M. incognita., Conclusion: Given the head-to-head orientation of DSC1 and WRKY19 in the Arabidopsis genome our data suggests that both genes may function as a TIR-NB-LRR immune receptor pair. Unlike other TIR-NB-LRR pairs involved in dominant disease resistance in plants, DSC1 and WRKY19 most likely regulate basal levels of immunity to root-knot nematodes.

Root-knot nematodes transform vascular host cells into permanent feeding structures to selectively withdraw their nutrients from host plants during the course of several weeks. The susceptibility of host plants to root-knot nematode infections is thought to be a complex trait involving many genetic loci. However, genome-wide association (GWA) analysis has so far revealed only four quantitative trait loci (QTLs) linked to the reproductive success of the root-knot nematode Meloidogyne incognita in Arabidopsis thaliana, which suggests that the genetic architecture underlying host susceptibility could be much simpler than previously thought. Here, we report that, by using a relaxed stringency approach in a GWA analysis, we could identify 15 additional loci linked to quantitative variation in the reproductive success of M. incognita in Arabidopsis. To test the robustness of our analysis, we functionally characterized six genes located in a QTL with the lowest acceptable statistical support and smallest effect size. This led us to identify ETHYLENE RESPONSE FACTOR 6 (ERF6) as a novel susceptibility gene for M. incognita in Arabidopsis. ERF6 functions as a transcriptional activator and suppressor of genes in response to various abiotic stresses independent of ethylene signalling. However, whole-transcriptome analysis of nematode-infected roots of the Arabidopsis erf6-1 knockout mutant line showed that allelic variation at this locus may regulate the conversion of aminocyclopropane-1-carboxylate (ACC) into ethylene by altering the expression of 1-aminocyclopropane-1-carboxylate oxidase 3 (ACO3). Our data further suggest that tolerance to abiotic stress mediated by ERF6 forms a novel layer of control in the susceptibility of Arabidopsis to M. incognita., (© 2018 The Authors. Molecular Plant Pathology published by BSPP and John Wiley & Sons Ltd.)

Susceptibility to the root-knot nematode Meloidogyne incognita in plants is thought to be a complex trait based on multiple genes involved in cell differentiation, growth and defence. Previous genetic analyses of susceptibility to M. incognita have mainly focused on segregating dominant resistance genes in crops. It is not known if plants harbour significant genetic variation in susceptibility to M. incognita independent of dominant resistance. To study the genetic architecture of susceptibility to M. incognita, we analysed nematode reproduction on a highly diverse set of 340 natural inbred lines of Arabidopsis thaliana with genome-wide association mapping. We observed a surprisingly large variation in nematode reproduction among these lines. Genome-wide association mapping revealed four quantitative trait loci (QTLs) located on chromosomes 1 and 5 of A. thaliana significantly associated with reproductive success of M. incognita, none of which harbours typical resistance gene homologues. Mutant analysis of three genes located in two QTLs showed that the transcription factor BRASSINAZOLE RESISTANT1 and an F-box family protein may function as (co-)regulators of susceptibility to M. incognita in Arabidopsis. Our data suggest that breeding for loss-of-susceptibility, based on allelic variants critically involved in nematode feeding, could be used to make crops more resilient to root-knot nematodes., (© 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.)

Plants are exposed to combinations of various biotic and abiotic stresses, but stress responses are usually investigated for single stresses only. Here, we investigated the genetic architecture underlying plant responses to 11 single stresses and several of their combinations by phenotyping 350 Arabidopsis thaliana accessions. A set of 214 000 single nucleotide polymorphisms (SNPs) was screened for marker-trait associations in genome-wide association (GWA) analyses using tailored multi-trait mixed models. Stress responses that share phytohormonal signaling pathways also share genetic architecture underlying these responses. After removing the effects of general robustness, for the 30 most significant SNPs, average quantitative trait locus (QTL) effect sizes were larger for dual stresses than for single stresses. Plants appear to deploy broad-spectrum defensive mechanisms influencing multiple traits in response to combined stresses. Association analyses identified QTLs with contrasting and with similar responses to biotic vs abiotic stresses, and below-ground vs above-ground stresses. Our approach allowed for an unprecedented comprehensive genetic analysis of how plants deal with a wide spectrum of stress conditions., (© 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.)

Plant-parasitic root-knot nematodes induce the formation of giant cells within the plant root, and it has been recognized that auxin accumulates in these feeding sites. Here, we studied the role of the auxin transport system governed by AUX1/LAX3 influx proteins and different PIN efflux proteins during feeding site development in Arabidopsis thaliana roots. Data generated via promoter-reporter line and protein localization analyses evoke a model in which auxin is being imported at the basipetal side of the feeding site by the concerted action of the influx proteins AUX1 and LAX3, and the efflux protein PIN3. Mutants in auxin influx proteins AUX1 and LAX3 bear significantly fewer and smaller galls, revealing that auxin import into the feeding sites is needed for their development and expansion. The feeding site development in auxin export (PIN) mutants was only slightly hampered. Expression of some PINs appears to be suppressed in galls, probably to prevent auxin drainage. Nevertheless, a functional PIN4 gene seems to be a prerequisite for proper nematode development and gall expansion, most likely by removing excessive auxin to stabilize the hormone level in the feeding site. Our data also indicate a role of local auxin peaks in nematode attraction towards the root., (© The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Despite causing considerable damage to host tissue during the onset of parasitism, nematodes establish remarkably persistent infections in both animals and plants. It is thought that an elaborate repertoire of effector proteins in nematode secretions suppresses damage-triggered immune responses of the host. However, the nature and mode of action of most immunomodulatory compounds in nematode secretions are not well understood. Here, we show that venom allergen-like proteins of plant-parasitic nematodes selectively suppress host immunity mediated by surface-localized immune receptors. Venom allergen-like proteins are uniquely conserved in secretions of all animal- and plant-parasitic nematodes studied to date, but their role during the onset of parasitism has thus far remained elusive. Knocking-down the expression of the venom allergen-like protein Gr-VAP1 severely hampered the infectivity of the potato cyst nematode Globodera rostochiensis. By contrast, heterologous expression of Gr-VAP1 and two other venom allergen-like proteins from the beet cyst nematode Heterodera schachtii in plants resulted in the loss of basal immunity to multiple unrelated pathogens. The modulation of basal immunity by ectopic venom allergen-like proteins in Arabidopsis thaliana involved extracellular protease-based host defenses and non-photochemical quenching in chloroplasts. Non-photochemical quenching regulates the initiation of the defense-related programmed cell death, the onset of which was commonly suppressed by venom allergen-like proteins from G. rostochiensis, H. schachtii, and the root-knot nematode Meloidogyne incognita. Surprisingly, these venom allergen-like proteins only affected the programmed cell death mediated by surface-localized immune receptors. Furthermore, the delivery of venom allergen-like proteins into host tissue coincides with the enzymatic breakdown of plant cell walls by migratory nematodes. We, therefore, conclude that parasitic nematodes most likely utilize venom allergen-like proteins to suppress the activation of defenses by immunogenic breakdown products in damaged host tissue.