A novel Arabidopsis pathosystem reveals cooperation of multiple hormonal response-pathways in host resistance against the global crop destroyer Macrophomina phaseolina.

Dubbed as a "global destroyer of crops", the soil-borne fungus Macrophomina phaseolina (Mp) infects more than 500 plant species including many economically important cash crops. Host defenses against infection by this pathogen are poorly understood. We established interactions between Mp and Arabidopsis thaliana (Arabidopsis) as a model system to quantitatively assess host factors affecting the outcome of Mp infections. Using agar plate-based infection assays with different Arabidopsis genotypes, we found signaling mechanisms dependent on the plant hormones ethylene, jasmonic acid and salicylic acid to control host defense against this pathogen. By profiling host transcripts in Mp-infected roots of the wild-type Arabidopsis accession Col-0 and ein2/jar1, an ethylene/jasmonic acid-signaling deficient mutant that exhibits enhanced susceptibility to this pathogen, we identified hundreds of genes potentially contributing to a diverse array of defense responses, which seem coordinated by complex interplay between multiple hormonal response-pathways. Our results establish Mp/Arabidopsis interactions as a useful model pathosystem, allowing for application of the vast genomics-related resources of this versatile model plant to the systematic investigation of previously understudied host defenses against a major crop plant pathogen

A specific group of genes respond to cold dehydration stress in cut Alstroemeria flowers whereas ambient dehydration stress accelerates developmental senescence expression patterns

Petal development and senescence entails a normally irreversible process. It starts with petal expansion and pigment production, and ends with nutrient remobilization and ultimately cell death. In many species this is accompanied by petal abscission. Post-harvest stress is an important factor in limiting petal longevity in cut flowers and accelerates some of the processes of senescence such as petal wilting and abscission. However, some of the effects of moderate stress in young flowers are reversible with appropriate treatments. Transcriptomic studies have shown that distinct gene sets are expressed during petal development and senescence. Despite this, the overlap in gene expression between developmental and stress-induced senescence in petals has not been fully investigated in any species. Here a custom-made cDNA microarray from Alstroemeria petals was used to investigate the overlap in gene expression between developmental changes (bud to first sign of senescence) and typical post-harvest stress treatments. Young flowers were stressed by cold or ambient temperatures without water followed by a recovery and rehydration period. Stressed flowers were still at the bud stage after stress treatments. Microarray analysis showed that ambient dehydration stress accelerates many of the changes in gene expression patterns that would normally occur during developmental senescence. However, a higher proportion of gene expression changes in response to cold stress were specific to this stimulus and not senescence related. The expression of 21 transcription factors was characterized, showing that overlapping sets of regulatory genes are activated during developmental senescence and by different stresses

Natural history of Arabidopsis thaliana and oomycete symbioses

Molecular ecology of plant–microbe interactions has immediate significance for filling a gap in knowledge between the laboratory discipline of molecular biology and the largely theoretical discipline of evolutionary ecology. Somewhere in between lies conservation biology, aimed at protection of habitats and the diversity of species housed within them. A seemingly insignificant wildflower called Arabidopsis thaliana has an important contribution to make in this endeavour. It has already transformed botanical research with deepening understanding of molecular processes within the species and across the Plant Kingdom; and has begun to revolutionize plant breeding by providing an invaluable catalogue of gene sequences that can be used to design the most precise molecular markers attainable for marker-assisted selection of valued traits. This review describes how A. thaliana and two of its natural biotrophic parasites could be seminal as a model for exploring the biogeography and molecular ecology of plant–microbe interactions, and specifically, for testing hypotheses proposed from the geographic mosaic theory of co-evolution

Transcriptome pathways unique to dehydration tolerant relatives of modern wheat

Among abiotic stressors, drought is a major factor responsible for dramatic yield loss in agriculture. In order to reveal differences in global expression profiles of drought tolerant and sensitive wild emmer wheat genotypes, a previously deployed shock-like dehydration process was utilized to compare transcriptomes at two time points in root and leaf tissues using the Affymetrix GeneChip(R) Wheat Genome Array hybridization. The comparison of transcriptomes reveal several unique genes or expression patterns such as differential usage of IP(3)-dependent signal transduction pathways, ethylene- and abscisic acid (ABA)-dependent signaling, and preferential or faster induction of ABA-dependent transcription factors by the tolerant genotype that distinguish contrasting genotypes indicative of distinctive stress response pathways. The data also show that wild emmer wheat is capable of engaging known drought stress responsive mechanisms. The global comparison of transcriptomes in the absence of and after dehydration underlined the gene networks especially in root tissues that may have been lost in the selection processes generating modern bread wheats

Co-option of EDM2 to distinct regulatory modules in Arabidopsis thaliana development

<p>Abstract</p> <p>Background</p> <p>Strong immunity of plants to pathogenic microorganisms is often mediated by highly specific mechanisms of non-self recognition that are dependent on disease resistance (<it>R</it>) genes. The <it>Arabidopsis thaliana </it>protein EDM2 is required for immunity mediated by the <it>R </it>gene <it>RPP7</it>. EDM2 is nuclear localized and contains typical features of transcriptional and epigenetic regulators. In addition, to its role in immunity, EDM2 plays also a role in promoting floral transition. This developmental function of EDM2, but not its role in <it>RPP7</it>-mediated disease resistance, seems to involve the protein kinase WNK8, which physically interacts with EDM2 in nuclei.</p> <p>Results</p> <p>Here we report that EDM2 affects additional developmental processes which include the formation of leaf pavement cells and leaf expansion as well as the development of morphological features related to vegetative phase change. EDM2 has a promoting effect of each of these processes. While WNK8 seems not to exhibit any vegetative phase change-related function, it has a promoting effect on the development of leaf pavement cells and leaf expansion. Microarray data further support regulatory interactions between WNK8 and EDM2. The fact that the effects of EDM2 and WNK8 on leaf pavement cell formation and leaf expansion are co-directional, while WNK8 counteracts the promoting effect of EDM2 on floral transition, is surprising and suggests that WNK8 can modulate the activity of EDM2.</p> <p>Conclusion</p> <p>We propose that EDM2 has been co-opted to distinct regulatory modules controlling a set of different processes in plant immunity and development. WNK8 appears to modulate some functions of EDM2.</p

WRR4, a broad-spectrum TIR-NB-LRR gene from Arabidopsis thaliana that confers white rust resistance in transgenic oilseed brassica crops

White blister rust caused by Albugo candida (Pers.) Kuntze is a common and often devastating disease of oilseed and vegetable brassica crops worldwide. Physiological races of the parasite have been described, including races 2, 7 and 9 from Brassica juncea, B. rapa and B. oleracea, respectively, and race 4 from Capsella bursa-pastoris (the type host). A gene named WRR4 has been characterized recently from polygenic resistance in the wild brassica relative Arabidopsis thaliana (accession Columbia) that confers broad-spectrum white rust resistance (WRR) to all four of the above Al. candida races. This gene encodes a TIR-NB-LRR (Toll-like/interleukin-1 receptor-nucleotide binding-leucine-rich repeat) protein which, as with other known functional members in this subclass of intracellular receptor-like proteins, requires the expression of the lipase-like defence regulator, enhanced disease susceptibility 1 (EDS1). Thus, we used RNA interference-mediated suppression of EDS1 in a white rust-resistant breeding line of B. napus (transformed with a construct designed from the A. thaliana EDS1 gene) to determine whether defence signalling via EDS1 is functionally intact in this oilseed brassica. The eds1-suppressed lines were fully susceptible following inoculation with either race 2 or 7 isolates of Al. candida. We then transformed white rust-susceptible cultivars of B. juncea (susceptible to race 2) and B. napus (susceptible to race 7) with the WRR4 gene from A. thaliana. The WRR4-transformed lines were resistant to the corresponding Al. candida race for each host species. The combined data indicate that WRR4 could potentially provide a novel source of white rust resistance in oilseed and vegetable brassica crops

The nuclear immune receptor RPS4 is required for RRS1SLH1-dependent constitutive defense activation in Arabidopsis thaliana

Plant nucleotide-binding leucine-rich repeat (NB-LRR) disease resistance (R) proteins recognize specific ‘‘avirulent’’ pathogen effectors and activate immune responses. NB-LRR proteins structurally and functionally resemble mammalian Nod-like receptors (NLRs). How NB-LRR and NLR proteins activate defense is poorly understood. The divergently transcribed Arabidopsis R genes, RPS4 (resistance to Pseudomonas syringae 4) and RRS1 (resistance to Ralstonia solanacearum 1), function together to confer recognition of Pseudomonas AvrRps4 and Ralstonia PopP2. RRS1 is the only known recessive NBLRR R gene and encodes a WRKY DNA binding domain, prompting suggestions that it acts downstream of RPS4 for transcriptional activation of defense genes. We define here the early RRS1-dependent transcriptional changes upon delivery of PopP2 via Pseudomonas type III secretion. The Arabidopsis slh1 (sensitive to low humidity 1) mutant encodes an RRS1 allele (RRS1SLH1) with a single amino acid (leucine) insertion in the WRKY DNA-binding domain. Its poor growth due to constitutive defense activation is rescued at higher temperature. Transcription profiling data indicate that RRS1SLH1-mediated defense activation overlaps substantially with AvrRps4- and PopP2-regulated responses. To better understand the genetic basis of RPS4/RRS1-dependent immunity, we performed a genetic screen to identify suppressor of slh1 immunity (sushi) mutants. We show that many sushi mutants carry mutations in RPS4, suggesting that RPS4 acts downstream or in a complex with RRS1. Interestingly, several mutations were identified in a domain C-terminal to the RPS4 LRR domain. Using an Agrobacterium-mediated transient assay system, we demonstrate that the P-loop motif of RPS4 but not of RRS1SLH1 is required for RRS1SLH1 function. We also recapitulate the dominant suppression of RRS1SLH1 defense activation by wild type RRS1 and show this suppression requires an intact RRS1 P-loop. These analyses of RRS1SLH1 shed new light on mechanisms by which NB-LRR protein pairs activate defense signaling, or are held inactive in the absence of a pathogen effector

Untersuchungen zur Darstellung von Hauptgruppenelementtetrazolverbindungen zur Übertragung auf d-Elemente

Im Rahmen dieser Arbeit wurde zuerst die Darstellung neuer N-silylierter und N-stannylierter Tetrazole untersucht. Durch nucleophile Substitution an Chlorsilanen konnten dabei die drei isomeren Bis(trimethylstannyltetrazol-5-yl)benzole 2 und das N,N'-Silacyclophan 4 isoliert und 1H-, 13C- und 29Si{1H}-NMR-spektroskopisch vollständig charakterisiert werden. 2a kris­tal­lisiert in der Raumgruppe P21/c (Nr. 14) mit den Gitterkonstanten a = 1162,3(2) pm, b = 1996,7(3) pm, c = 853,8(1) pm, β = 99,1(2)° und Z = 4, wobei die (CH3)3Si-Gruppen je einmal an N1 und einmal an N2 gebunden sind. Die Untersuchungen zur Darstellung eines Pentafluorphenyltetrazolderivats zeigten, dass auf Grund der Fluorophilie des Siliciums eine nucleophile aromatische Substition am 4-F des C6F5CN eintritt, statt einer Cycloaddition von (CH3)3SiN3 mit C6F5CN. Das erste Pentafluorphenyltetrazolderivat konnte durch die Cycloaddition mit dem weniger fluorophilen (CH3)3SnN3 isoliert werden. (CH3)3SnN4CC6F5 11 wurde 1H-, 13C-, 19F- und 119Sn{1H}-NMR-spektroskopisch vollständig charakterisiert. Durch Reaktion von (CH3)3SnN3 mit s-(CN)3C3N3 12 konnte das erste homoleptische Tetrazol-5-yltriazin s-((CH3)3SnN4C)3C3N3 als Lösungsmitteladdukt 13·DMF isoliert werden. 13·DMF wurde 1H-, 13C- und 119Sn{1H}-NMR-spektroskopisch vollständig charakterisiert. Bei Unter­suchungen zur Hydrolysierbarkeit wurden Kristalle des 4,6-Bis(2-tri­methyl­stan­nyl-tetrazol-5-yl)-1,3,5-triazin-2-on-Derivats 14·H2O erhalten und röntgenographisch untersucht. 14·H2O kristallisiert in der Raumgruppe Pmnb (Nr. 62) mit den Gitterkonstanten a = 1335,6(2) pm, b = 1434,0(2) pm, c = 1737,7(3) pm und Z = 8. Die Struktur enthält ein penta- und ein heptakoordiniertes Sn-Atom. Im Rahmen der Untersuchung zur Darstellung neuer d-Gruppen­element-Tetrazolen konnte durch Reaktionen in wässriger Lösung die BTB-Komplexe des Silbers 15a und Quecksilbers 15b isoliert werden. Durch Cycloaddition des nach R. Haiges et. al[60] in situ dargestellten [Ti(N3)6]2- mit CF3CN konnte der erste homoleptische Tetrazolatokomplex des Titans [N(CH3)4]2[Ti(N4CCF3)6] 16 isoliert und vollständig 1H-, 13C- und 19F-NMR-spektroskopisch charakterisiert werden. Durch Reaktion des 2a mit [N(CH3)4]2[TiF6] konnte der zweite homoleptische Tetrazolatokomplex des Titans [N(CH3)4]2[Ti(BTB)3] 17 isoliert und vollständig 1H- und 13C-NMR-spektroskopisch charakterisiert werden. In beiden Titan­komplexen sind die Tetrazolatoliganden auf der NMR-Zeitskala magnetisch äquivalent, die Geometrie um die Zentralatome ist folglich oktaedrisch