Chromosome and genome stability are important for normal cell function as instability often correlates with disease and dysfunction of DNA repair mechanisms. Many organisms maintain supernumerary or accessory chromosomes that deviate from standard chromosomes. The pathogenic fungus Zymoseptoria tritici has as many as eight accessory chromosomes, which are highly unstable during meiosis and mitosis, transcriptionally repressed, show enrichment of repetitive elements, and enrichment with heterochromatic histone methylation marks, e.g., trimethylation of H3 lysine 9 or lysine 27 (H3K9me3, H3K27me3). To elucidate the role of heterochromatin on genome stability in Z . tritici , we deleted the genes encoding the methyltransferases responsible for H3K9me3 and H3K27me3, kmt1 and kmt6 , respectively, and generated a double mutant. We combined experimental evolution and genomic analyses to determine the impact of these deletions on chromosome and genome stability, both in vitro and in planta . We used whole genome sequencing, ChIP-seq, and RNA-seq to compare changes in genome and chromatin structure, and differences in gene expression between mutant and wildtype strains. Analyses of genome and ChIP-seq data in H3K9me3-deficient strains revealed dramatic chromatin reorganization, where H3K27me3 is mostly relocalized into regions that are enriched with H3K9me3 in wild type. Many genome rearrangements and formation of new chromosomes were found in the absence of H3K9me3, accompanied by activation of transposable elements. In stark contrast, loss of H3K27me3 actually increased the stability of accessory chromosomes under normal growth conditions in vitro , even without large scale changes in gene activity. We conclude that H3K9me3 is important for the maintenance of genome stability because it disallows H3K27me3 in regions considered constitutive heterochromatin. In this system, H3K27me3 reduces the overall stability of accessory chromosomes, generating a “metastable” state for these quasi-essential regions of the genome.

27Chromosome and genome stability are important for normal cell function as instability often 28 correlates with disease and dysfunction of DNA repair mechanisms. Many organisms maintain 29 supernumerary or accessory chromosomes that deviate from standard chromosomes. The 30 pathogenic fungus Zymoseptoria tritici has as many as eight accessory chromosomes, which are 31 highly unstable during meiosis and mitosis, transcriptionally repressed, show enrichment of 32 repetitive elements, and enrichment with heterochromatic histone methylation marks, e.g., 33trimethylation of H3 lysine 9 or lysine 27 (H3K9me3, H3K27me3). To elucidate the role of 34 heterochromatin on genome stability in Z. tritici, we deleted the genes encoding the 35 methyltransferases responsible for H3K9me3 and H3K27me3, kmt1 and kmt6, respectively, and 36 generated a double mutant. We combined experimental evolution and genomic analyses to 37 determine the impact of these deletions on chromosome and genome stability, both in vitro and 38 in planta. We used whole genome sequencing, ChIP-seq, and RNA-seq to compare changes in 39 genome and chromatin structure, and differences in gene expression between mutant and 40 wildtype strains. Analyses of genome and ChIP-seq data in H3K9me3-deficient strains revealed 41 dramatic chromatin reorganization, where H3K27me3 is mostly relocalized into regions that are 42 enriched with H3K9me3 in wild type. Many genome rearrangements and formation of new 43 chromosomes were found in the absence of H3K9me3, accompanied by activation of transposable 44 elements. In stark contrast, loss of H3K27me3 actually increased the stability of accessory 45 chromosomes under normal growth conditions in vitro, even without large scale changes in gene 46 activity. We conclude that H3K9me3 is important for the maintenance of genome stability 47 because it disallows H3K27me3 in these regions. In this system, H3K27me3 reduces the overall 48 stability of accessory chromosomes, generating a "metastable" state for these quasi-essential 49 regions of the genome. 50 3 Author Summary 51 Genome and chromosome stability are essential to maintain normal cell function and viability. 52However, differences in genome and chromosome structure are frequently found in organisms 53 that undergo rapid adaptation to changing environmental conditions, and in humans are often 54 found in cancer cells. We study genome instability in a fungal pathogen that exhibits a high degree 55 of genetic diversity. Regions that show extraordinary diversity in this pathogen are the 56 transposon-rich accessory chromosomes, which contain few genes that are of unknown benefit 57 to the organism but maintained in the population and thus considered "quasi essential". 58Accessory chromosomes in all fungi studied so far are enriched with markers for 59 heterochromatin, namely trimethylation of H3 lysine 9 and 27 (H3K9me3, H3K27me3). We show 60 that loss of these heterochromatin marks has strong but opposing effects on genome stability. 61While loss of the transposon-associate...

The lectin-like oxidized LDL receptor 1 (LOX-1) is a key player in the development of atherosclerosis. LOX-1 promotes endothelial activation and dysfunction by mediating uptake of oxidized LDL and inducing pro-atherogenic signaling. However, little is known about modulators of LOX-1–mediated responses. Here, we show that the function of LOX-1 is controlled proteolytically. Ectodomain shedding by the metalloprotease ADAM10 and lysosomal degradation generate membrane-bound N-terminal fragments (NTFs), which we identified as novel substrates of the intramembrane proteases signal peptide peptidase–like 2a and b (SPPL2a/b). SPPL2a/b control cellular LOX-1 NTF levels which, following self-association via their transmembrane domain, can activate MAP kinases in a ligand-independent manner. This leads to an up-regulation of several pro-atherogenic and pro-fibrotic targets including ICAM-1 and the connective tissue growth factor CTGF. Consequently, SPPL2a/b-deficient mice, which accumulate LOX-1 NTFs, develop larger and more advanced atherosclerotic plaques than controls. This identifies intramembrane proteolysis by SPPL2a/b as a novel atheroprotective mechanism via negative regulation of LOX-1 signaling.

Charophyte green algae (CGA) are assigned to be the closest relatives of land plants and therefore enlighten processes in the colonization of terrestrial habitats. For the transition from water to land, plants needed significant physiological and structural changes, as well as with regard to cell wall composition. Sequential extraction of cell walls of Nitellopsis obtusa (Charophyceae) and Spirogyra pratensis (Zygnematophyceae) offered a comparative overview on cell wall composition of late branching CGA. Because arabinogalactanproteins (AGPs) are considered common for all land plant cell walls, we were interested in whether these special glycoproteins are present in CGA. Therefore, we investigated both species with regard to characteristic features of AGPs. In the cell wall of Nitellopsis, no hydroxyproline was present and no AGP was precipitable with the b-glucosyl Yariv's reagent (bGlcY). By contrast, bGlcY precipitation of the water-soluble cell wall fraction of Spirogyra yielded a glycoprotein fraction rich in hydroxyproline, indicating the presence of AGPs. Putative AGPs in the cell walls of non-conjugating Spirogyra filaments, especially in the area of transverse walls, were detected by staining with bGlcY. Labelling increased strongly in generative growth stages, especially during zygospore development. Investigations of the fine structure of the glycan part of bGlcYprecipitated molecules revealed that the galactan backbone resembled that of AGPs with 1,3-1,6-and 1,3,6linked Galp moieties. Araf was present only in small amounts and the terminating sugars consisted predominantly of pyranosidic terminal and 1,3-linked rhamnose residues. We introduce the term 'rhamnogalactanprotein' for this special AGP-modification present in S. pratensis.

The thalloid liverwort Marchantia polymorpha as a member of a basal land plant lineage has to cope with the challenge of terrestrial life. Obviously, the plant cell wall has been strongly involved in the outstanding evolutionary process of water-to-land-transition. AGPs are signaling glycoproteins of the cell wall, which seem to be ubiquitous in seed plants and might play a role in adaption to abiotic and biotic stress situations. Therefore, we investigated the cell wall composition of Marchantia polymorpha with special focus on structural characterization of arabinogalactan-proteins. The Marchantia AGP shows typical features known from seed plant AGPs like precipitation with β-glucosyl-Yariv’s reagent, a protein moiety with hydroxyproline and a carbohydrate part with 1,3,6-linked galactose and terminal arabinose residues. On the other hand, striking differences to AGPs of angiosperms are the occurrence of terminal 3-O-methyl-rhamnose and a highly branched galactan lacking appreciable amounts of 1,6-linked galactose. Binding of different AGP-antibodies (JIM13, KM1, LM2, LM6, LM14, LM26, and MAC207) to Marchantia AGP was investigated and confirmed structural differences between liverwort and angiosperm AGP, possibly due to deviating functions of these signaling molecules in the different taxonomic groups.