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Publikation

Wasternack, C.; Strnad, M. Jasmonates: News on Occurrence, Biosynthesis, Metabolism and Action of an Ancient Group of Signaling Compounds Int J Mol Sci 19, 2539, (2018) DOI: 10.3390/ijms19092539

Jasmonic acid (JA) and its related derivatives are ubiquitously occurring compounds of land plants acting in numerous stress responses and development. Recent studies on evolution of JA and other oxylipins indicated conserved biosynthesis. JA formation is initiated by oxygenation of α-linolenic acid (α-LeA, 18:3) or 16:3 fatty acid of chloroplast membranes leading to 12-oxo-phytodienoic acid (OPDA) as intermediate compound, but in Marchantiapolymorpha and Physcomitrellapatens, OPDA and some of its derivatives are final products active in a conserved signaling pathway. JA formation and its metabolic conversion take place in chloroplasts, peroxisomes and cytosol, respectively. Metabolites of JA are formed in 12 different pathways leading to active, inactive and partially active compounds. The isoleucine conjugate of JA (JA-Ile) is the ligand of the receptor component COI1 in vascular plants, whereas in the bryophyte M. polymorpha COI1 perceives an OPDA derivative indicating its functionally conserved activity. JA-induced gene expressions in the numerous biotic and abiotic stress responses and development are initiated in a well-studied complex regulation by homeostasis of transcription factors functioning as repressors and activators.
Publikation

Bagchi, R.; Melnyk, C. W.; Christ, G.; Winkler, M.; Kirchsteiner, K.; Salehin, M.; Mergner, J.; Niemeyer, M.; Schwechheimer, C.; Calderón Villalobos, L. I. A.; Estelle, M. The Arabidopsis ALF4 protein is a regulator of SCF E3 ligases. EMBO J 37, 255-268, (2018) DOI: 10.15252/embj.201797159

The cullin-RING E3 ligases (CRLs) regulate diverse cellular processes in all eukaryotes. CRL activity is controlled by several proteins or protein complexes, including NEDD8, CAND1, and the CSN. Recently, a mammalian protein called Glomulin (GLMN) was shown to inhibit CRLs by binding to the RING BOX (RBX1) subunit and preventing binding to the ubiquitin-conjugating enzyme. Here, we show that Arabidopsis ABERRANT LATERAL ROOT FORMATION4 (ALF4) is an ortholog of GLMN. The alf4 mutant exhibits a phenotype that suggests defects in plant hormone response. We show that ALF4 binds to RBX1 and inhibits the activity of SCFTIR1, an E3 ligase responsible for degradation of the Aux/IAA transcriptional repressors. In vivo, the alf4 mutation destabilizes the CUL1 subunit of the SCF. Reduced CUL1 levels are associated with increased levels of the Aux/IAA proteins as well as the DELLA repressors, substrate of SCFSLY1. We propose that the alf4 phenotype is partly due to increased levels of the Aux/IAA and DELLA proteins.
Publikation

Wasternack, C. A plant's balance of growth and defense - revisited New Phytol 215, 1291-1294, (2017) DOI: 10.1111/nph.14720

This article is a Commentary on Major et al., 215: 1533–1547.
Publikation

Wasternack, C. The Trojan horse coronatine: the COI1–JAZ2–MYC2,3,4–ANAC019,055,072 module in stomata dynamics upon bacterial infection. New Phytol 213, 972-975, (2017) DOI: 10.1111/nph.14417

Coronatine (COR) is a phytotoxin produced by a plasmid-encoded operon of genes in several strains of Pseudomonas syringae (Bender et al., 1999). It is a mimic of the defense-associated phytohormone jasmonic acid isoleucine and delivered by the phytopathogenic bacterium to gain access to host plants through stomatal entry and to repress a specific sector of plant immunity. In this issue of New Phytologist (pp. 1378–1392) Gimenez-Ibanez et al. reveal exciting insights into the transcriptional regulation of COR/jasmonic acid isoleucine-governed transcriptional networks modulating stomatal aperture during bacterial invasion.
Publikation

Strehmel, N.; Mönchgesang, S.; Herklotz, S.; Krüger, S.; Ziegler, J.; Scheel, D. Piriformospora indica Stimulates Root Metabolism of Arabidopsis thaliana Int J Mol Sci 17, 1091, (2016) DOI: 10.3390/ijms17071091

Piriformospora indica is a root-colonizing fungus, which interacts with a variety of plants including Arabidopsis thaliana. This interaction has been considered as mutualistic leading to growth promotion of the host. So far, only indolic glucosinolates and phytohormones have been identified as key players. In a comprehensive non-targeted metabolite profiling study, we analyzed Arabidopsis thaliana’s roots, root exudates, and leaves of inoculated and non-inoculated plants by ultra performance liquid chromatography/electrospray ionization quadrupole-time-of-flight mass spectrometry (UPLC/(ESI)-QTOFMS) and gas chromatography/electron ionization quadrupole mass spectrometry (GC/EI-QMS), and identified further biomarkers. Among them, the concentration of nucleosides, dipeptides, oligolignols, and glucosinolate degradation products was affected in the exudates. In the root profiles, nearly all metabolite levels increased upon co-cultivation, like carbohydrates, organic acids, amino acids, glucosinolates, oligolignols, and flavonoids. In the leaf profiles, we detected by far less significant changes. We only observed an increased concentration of organic acids, carbohydrates, ascorbate, glucosinolates and hydroxycinnamic acids, and a decreased concentration of nitrogen-rich amino acids in inoculated plants. These findings contribute to the understanding of symbiotic interactions between plant roots and fungi of the order of Sebacinales and are a valid source for follow-up mechanistic studies, because these symbioses are particular and clearly different from interactions of roots with mycorrhizal fungi or dark septate endophytes 
Publikation

Farmer, E. E.; Gasperini, D.; Acosta, I. F. The squeeze cell hypothesis for the activation of jasmonate synthesis in response to wounding New Phytol 204, 282-288, (2014) DOI: 10.1111/nph.12897

Jasmonates are lipid mediators that control defence gene expression in response to wounding and other environmental stresses. These small molecules can accumulate at distances up to several cm from sites of damage and this is likely to involve cell‐to‐cell jasmonate transport. Also, and independently of jasmonate synthesis, transport and perception, different long‐distance wound signals that stimulate distal jasmonate synthesis are propagated at apparent speeds of several cm min–1 to tissues distal to wounds in a mechanism that involves clade 3 GLUTAMATE RECEPTOR‐LIKE (GLR) genes. A search for jasmonate synthesis enzymes that might decode these signals revealed LOX6, a lipoxygenase that is necessary for much of the rapid accumulation of jasmonic acid at sites distal to wounds. Intriguingly, the LOX6 promoter is expressed in a distinct niche of cells that are adjacent to mature xylem vessels, a location that would make these contact cells sensitive to the release of xylem water column tension upon wounding. We propose a model in which rapid axial changes in xylem hydrostatic pressure caused by wounding travel through the vasculature and lead to slower, radially dispersed pressure changes that act in a clade 3 GLR‐dependent mechanism to promote distal jasmonate synthesis.
Publikation

Antolín-Llovera, M.; Petutsching, E. K.; Ried, M. K.; Lipka, V.; Nürnberger, T.; Robatzek, S.; Parniske, M. Knowing your friends and foes - plant receptor-like kinases as initiators of symbiosis or defence New Phytol 204, 791-802, (2014) DOI: 10.1111/nph.13117

The decision between defence and symbiosis signalling in plants involves alternative and modular plasma membrane‐localized receptor complexes. A critical step in their activation is ligand‐induced homo‐ or hetero‐oligomerization of leucine‐rich repeat (LRR)‐ and/or lysin motif (LysM) receptor‐like kinases (RLKs). In defence signalling, receptor complexes form upon binding of pathogen‐associated molecular patterns (PAMPs), including the bacterial flagellin‐derived peptide flg22, or chitin. Similar mechanisms are likely to operate during the perception of microbial symbiont‐derived (lipo)‐chitooligosaccharides. The structurally related chitin‐oligomer ligands chitooctaose and chitotetraose trigger defence and symbiosis signalling, respectively, and their discrimination involves closely related, if not identical, LysM‐RLKs. This illustrates the demand for and the challenges imposed on decision mechanisms that ensure appropriate signal initiation. Appropriate signalling critically depends on abundance and localization of RLKs at the cell surface. This is regulated by internalization, which also provides a mechanism for the removal of activated signalling RLKs. Abundance of the malectin‐like domain (MLD)‐LRR‐RLK Symbiosis Receptor‐like Kinase (SYMRK) is additionally controlled by cleavage of its modular ectodomain, which generates a truncated and rapidly degraded RLK fragment. This review explores LRR‐ and LysM‐mediated signalling, the involvement of MLD‐LRR‐RLKs in symbiosis and defence, and the role of endocytosis in RLK function.
Publikation

Stumpe, M.; Göbel, C.; Faltin, B.; Beike, A. K.; Hause, B.; Himmelsbach, K.; Bode, J.; Kramell, R.; Wasternack, C.; Frank, W.; Reski, R.; Feussner, I. The moss Physcomitrella patens contains cyclopentenones but no jasmonates: mutations in allene oxide cyclase lead to reduced fertility and altered sporophyte morphology New Phytol 188 (3), 740-749, (2010) DOI: 10.1111/j.1469-8137.2010.03406.x

Two cDNAs encoding allene oxide cyclases (PpAOC1, PpAOC2), key enzymes in the formation of jasmonic acid (JA) and its precursor (9S,13S)‐12‐oxo‐phytodienoic acid (cis‐(+)‐OPDA), were isolated from the moss Physcomitrella patens.Recombinant PpAOC1 and PpAOC2 show substrate specificity against the allene oxide derived from 13‐hydroperoxy linolenic acid (13‐HPOTE); PpAOC2 also shows substrate specificity against the allene oxide derived from 12‐hydroperoxy arachidonic acid (12‐HPETE).In protonema and gametophores the occurrence of cis‐(+)‐OPDA, but neither JA nor the isoleucine conjugate of JA nor that of cis‐(+)‐OPDA was detected.Targeted knockout mutants for PpAOC1 and for PpAOC2 were generated, while double mutants could not be obtained. The ΔPpAOC1 and ΔPpAOC2 mutants showed reduced fertility, aberrant sporophyte morphology and interrupted sporogenesis.
Publikation

Clarke, S.M.; Cristescu, S.M.; Miersch, O.; Harren, F.J.M.; Wasternack, C.; Mur, L.A.J. Jasmonates act with salicylic acid to confer basal thermotolerance in <i>Arabidopsis thaliana</i> New Phytol 182, 175-187, (2009) DOI: 10.1111/j.1469-8137.2008.02735.x

The cpr5-1 Arabidopsis thaliana mutant exhibits constitutive activation of salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) signalling pathways and displays enhanced tolerance of heat stress (HS). cpr5-1 crossed with jar1-1 (a JA-amino acid synthetase) was compromised in basal thermotolerance, as were the mutants opr3 (mutated in OPDA reductase3) and coi1-1 (affected in an E3 ubiquitin ligase F-box; a key JA-signalling component). In addition, heating wild-type Arabidopsis led to the accumulation of a range of jasmonates: JA, 12-oxophytodienoic acid (OPDA) and a JA-isoleucine (JA-Ile) conjugate. Exogenous application of methyl jasmonate protected wild-type Arabidopsis from HS. Ethylene was rapidly produced during HS, with levels being modulated by both JA and SA. By contrast, the ethylene mutant ein2-1 conferred greater thermotolerance. These data suggest that JA acts with SA, conferring basal thermotolerance while ET may act to promote cell death.
Publikation

Abel, S.; Savchenko, T.; Levy, M. Genome-wide comparative analysis of the <em>IQD</em> gene families in <em>Arabidopsis thaliana</em> and Oryza sativa BMC Evolutionary Biology 5, 72 (1-25), (2005)

We identified and analyzed 33 and 29 IQD1-like genes in Arabidopsis thaliana and Oryza sativa, respectively. The encoded IQD proteins contain a plant-specific domain of 67 conserved amino acid residues, referred to as the IQ67 domain, which is characterized by a unique and repetitive arrangement of three different calmodulin recruitment motifs, known as the IQ, 1-5-10, and 1-8-14 motifs. We demonstrated calmodulin binding for IQD20, the smallest IQD protein in Arabidopsis, which consists of a C-terminal IQ67 domain and a short N-terminal extension. A striking feature of IQD proteins is the high isoelectric point (~10.3) and frequency of serine residues (~11%). We compared the Arabidopsis and rice IQD gene families in terms of gene structure, chromosome location, predicted protein properties and motifs, phylogenetic relationships, and evolutionary history. The existence of an IQD-like gene in bryophytes suggests that IQD proteins are an ancient family of calmodulin-binding proteins and arose during the early evolution of land plants. Comparative phylogenetic analyses indicate that the major IQD gene lineages originated before the monocot-eudicot divergence. The extant IQD loci in Arabidopsis primarily resulted from segmental duplication and reflect preferential retention of paralogous genes, which is characteristic for proteins with regulatory functions. Interaction of IQD1 and IQD20 with calmodulin and the presence of predicted calmodulin binding sites in all IQD family members suggest that IQD proteins are a new class of calmodulin targets. The basic isoelectric point of IQD proteins and their frequently predicted nuclear localization suggest that IQD proteins link calcium signaling pathways to the regulation of gene expression. Our comparative genomics analysis of IQD genes and encoded proteins in two model plant species provides the first step towards the functional dissection of this emerging family of putative calmodulin targets.
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