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  • 1.
    Chakravarthy, Suma
    et al.
    BTI, Cornell University, USA.
    Velasquez, A.C.
    BTI, Cornell University, USA.
    Ekengren, Sophia
    Stockholm University.
    Martin, Gregory M.
    BTI, Cornell University, USA.
    Identification of Nicotiana benthamiana genes involved in pathogen-associated molecular pattern-triggered immunity2010In: Molecular Plant-Microbe Interactions, ISSN 0894-0282, E-ISSN 1943-7706, Vol. 23, no 6, p. 715-726Article in journal (Refereed)
    Abstract [en]

    In order to identify components of pathogen-associated molecular pattern triggered immunity (PTI) pathways in Nicotiana benthamiana, we conducted a large-scale forward-genetics screen using virus-induced gene silencing and a cell-death-based assay for assessing PTI. The assay relied on four combinations of PTI-inducing nonpathogens and cell-death-causing challenger pathogens and was first validated in plants silenced for FLS2 or BAK1. Over 3,200 genes were screened and 14 genes were identified that, when silenced, compromised PTI as judged by the cell-death-based assay. Further analysis indicated that the 14 genes were not involved in a general cell death response. A subset of the genes was found to act downstream of FLS2-mediated PTI induction, and silencing of three genes compromised production of reactive oxygen species in leaves exposed to fig22. The 14 genes encode proteins with potential functions in defense and hormone signaling, protein stability and degradation, energy and secondary metabolism, and cell wall biosynthesis and provide a new resource to explore the molecular basis for the involvement of these processes in PTI.

  • 2.
    Chandok, Meena, R.
    et al.
    BTI, Cornell University, USA.
    Ekengren, Sophia K.
    BTI, Cornell University, USA.
    Martin, Gregory, B.
    BTI, Cornell University.
    Klessig, Daniel, F.
    BTI, Cornell University, USA.
    Individual Suppression of pathogen-inducible NO synthase (iNOS) activity in tomato increases susceptibility to Pseudomonas syringae2004In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 101, p. 8239-8244Article in journal (Refereed)
  • 3. Chiasson, David
    et al.
    Ekengren, Sophia K.
    BTI, Cornell University, USA.
    Martin, G.B.
    Dobney, S.L.
    Snedden, W.A.
    Calmodulin-like proteins from Arabidopsis and tomato are involved in host defense against Pseudomonas syringae pv. tomato2005In: Plant Molecular Biology, ISSN 0167-4412, E-ISSN 1573-5028, Vol. 58, no 6, p. 887-897Article in journal (Refereed)
    Abstract [en]

    Complex signal transduction pathways underlie the myriad plant responses to attack by pathogens. Ca-2 is a universal second messenger in eukaryotes that modulates various signal transduction pathways through stimulus-specific changes in its intracellular concentration. Ca2+-binding proteins such as calmodulin (CaM) detect Ca2+ signals and regulate downstream targets as part of a coordinated cellular response to a given stimulus. Here we report the characterization of a tomato gene (APR134) encoding a CaM-related protein that is induced in disease-resistant leaves in response to attack by Pseudomonas syringae pv. tomato. We show that suppression of APR134 gene expression in tomato (Solanum lycopersicum), using virus-induced gene silencing (VIGS), compromises the plant's immune response. We isolated APR134-like genes from Arabidopsis, termed CML42 and CML43, to investigate whether they serve a functionally similar role. Gene expression analysis revealed that CML43 is rapidly induced in disease-resistant Arabidopsis leaves following inoculation with Pseudomonas syringae pv. tomato. Overexpression of CML43 in Arabidopsis accelerated the hypersensitive response. Recombinant APR134, CML42, and CML43 proteins all bind Ca2+ in vitro. Collectively, our data support a role for CML43, and APR134 as important mediators of Ca2+-dependent signals during the plant immune response to bacterial pathogens.

  • 4.
    Clergeot, Pierre-Henri
    et al.
    Stockholm University.
    Rivetti, Claudia
    Stockholm University.
    Hamiduzzaman, M. Md.
    Stockholm University.
    Ekengren, Sophia
    Stockholm University.
    The corky root rot pathogen, Pyrenochaeta lycopersici manipulates tomato roots with molecules secreted early during their interaction2012In: Acta Agriculturae Scandinavica - Section B, ISSN 0906-4710, E-ISSN 1651-1913, Vol. 62, no 4, p. 300-310Article in journal (Refereed)
    Abstract [en]

    Corky root rot is a ubiquitous soil-borne disease of tomato caused by the pathogen Pyrenochaeta lycopersici. This filamentous fungus is found on the roots of many crops and can persist in the soil up to 15 years as microsclerotia. High prevalence of corky root rot can be partly explained by the endurance and the broad host range of P. lycopersici, but how this fungus can gain access to host roots is still poorly understood, as its competitive saprophytic ability is very low. We have combined microscopy and reporter gene techniques to investigate the tomato-P. lycopersici interaction in vitro, and discovered the pathogen secretes molecules that change the direction of root growth and induce cell necrosis specifically in the apical part of the root of tomato ( apex, elongation zone and beginning of the root hair zone). Moreover, we found that the fungus preferentially infects immature root cells that are sensitive to these secreted fungal molecules, whereas infection is blocked in mature and insensitive parts of the root. Our study sheds light on novel and important features of the biology of this pathogen, which could contribute to its fitness in the rhizosphere.

  • 5.
    Dahlin, Paul
    et al.
    KTH, School of Biotechnology (BIO), Glycoscience. Stockholm Univ, Sweden.
    Müller, Marion C.
    KTH, School of Biotechnology (BIO), Glycoscience. Stockholm Univ, Sweden.
    Ekengren, Sophia
    KTH, School of Biotechnology (BIO), Glycoscience. Stockholm Univ, Sweden.
    McKee, Lauren S.
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Bulone, Vincent
    KTH, School of Biotechnology (BIO), Glycoscience. Univ Adelaide, Australia.
    The Impact of Steroidal Glycoalkaloids on the Physiology of Phytophthora infestans, the Causative Agent of Potato Late Blight2017In: Molecular Plant-Microbe Interactions, ISSN 0894-0282, E-ISSN 1943-7706, Vol. 30, no 7, p. 531-542Article in journal (Refereed)
    Abstract [en]

    Steroidal glycoalkaloids (SGAs) are plant secondary metabolites known to be toxic to animals and humans and that have putative roles in defense against pests. The proposed mechanisms of SGA toxicity are sterol-mediated disruption of membranes and inhibition of cholinesterase activity in neurons. It has been suggested that phytopathogenic microorganisms can overcome SGA toxicity by enzymatic deglycosylation of SGAs. Here, we have explored SGA-mediated toxicity toward the invasive oomycete Phytophthora infestans, the causative agent of the late blight disease in potato and tomato, as well as the potential for SGA deglycosylation by this species. Our growth studies indicate that solanidine, the nonglycosylated precursor of the potato SGAs a-chaconine and a-solanine, has a greater physiological impact than its glycosylated forms. All of these compounds were incorporated into the mycelium, but only solanidine could strongly inhibit the growth of P. infestans in liquid culture. Genes encoding several glycoside hydrolases with potential activity on SGAs were identified in the genome of P. infestans and were shown to be expressed. However, we found no indication that deglycosylation of SGAs takes place. We present additional evidence for apparent host-specific adaptation to potato SGAs and assess all results in terms of future pathogen management strategies.

  • 6.
    Dahlin, Paul
    et al.
    KTH, School of Biotechnology (BIO), Glycoscience.
    Srivastava, Vaibhav
    KTH, School of Biotechnology (BIO), Glycoscience.
    Ekengren, Sophia
    KTH, School of Biotechnology (BIO), Glycoscience.
    McKee, Lauren S.
    KTH, School of Biotechnology (BIO), Glycoscience.
    Bulone, Vincent
    KTH, School of Biotechnology (BIO), Glycoscience.
    Comparative analysis of sterol acquisition in the oomycetes Saprolegnia parasitica and Phytophthora infestans2017In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, no 2, article id e0170873Article in journal (Refereed)
    Abstract [en]

    The oomycete class includes pathogens of animals and plants which are responsible for some of the most significant global losses in agriculture and aquaculture. There is a need to replace traditional chemical means of controlling oomycete growth with more targeted approaches, and the inhibition of sterol synthesis is one promising area. To better direct these efforts, we have studied sterol acquisition in two model organisms: the sterol-autotrophic Saprolegnia parasitica, and the sterol-heterotrophic Phytophthora infestans. We first present a comprehensive reconstruction of a likely sterol synthesis pathway for S. parasitica, causative agent of the disease saprolegniasis in fish. This pathway shows multiple potential routes of sterol synthesis, and draws on several avenues of new evidence: bioinformatic mining for genes with sterol-related functions, expression analysis of these genes, and analysis of the sterol profiles in mycelium grown in different media. Additionally, we explore the extent to which P. infestans, which causes the late blight in potato, can modify exogenously provided sterols. We consider whether the two very different approaches to sterol acquisition taken by these pathogens represent any specific survival advantages or potential drug targets.

  • 7.
    Devarenne, Tim, P.
    et al.
    BTI, Cornell University, USA.
    Ekengren, Sophia K.
    BTI, Cornell University, USA.
    Pedley, K. F.
    BTI, Cornell University, USA.
    Martin, Gregory, B.
    BTI, Cornell University.
    Adi3 is a Pdk1-interacting AGC kinase that negatively regulates plant cell death2006In: EMBO Journal, ISSN 0261-4189, E-ISSN 1460-2075, Vol. 25, no 1, p. 255-265Article in journal (Refereed)
    Abstract [en]

    Bacterial speck disease in tomato is caused by Pseudomonas syringae pv. tomato. Resistance to this disease is conferred by the host Pto kinase, which recognizes P. s. pv. tomato strains that express the effector AvrPto. We report here that an AvrPto-dependent Pto-interacting protein 3 (Adi3) is a member of the AGC family of protein kinases. In mammals, AGC kinases are regulated by 3-phosphoinositide-dependent protein kinase-1 (Pdk1). We characterized tomato Pdk1 and showed that Pdk1 and Pto phosphorylate Adi3. Gene silencing of Adi3 in tomato causes MAPKKK alpha-dependent formation of necrotic lesions. Use of a chemical inhibitor of Pdk1, OSU-03012, also implicates Pdk1 and Adi3 in plant cell death regulation. Adi3 thus appears to function analogously to the mammalian AGC kinase protein kinase B/Akt by negatively regulating cell death via Pdk1 phosphorylation. We speculate that the negative regulatory function of Adi3 might be subverted by interaction with Pto/AvrPto, leading to host cell death that is associated with pathogen attack.

  • 8.
    Ekengren, Sophia
    Stockholm University.
    Cutting the Gordian knot: taking a stab at corky root rot of tomato2008In: Plant Biotechnology, ISSN 1342-4580, Vol. 25, no 3, p. 265-269Article in journal (Refereed)
    Abstract [en]

    Corky root rot (CRR) is an escalating plant disease of tomato (Solanum esculentum), caused by a soil-borne fungus, Pyrenochaeta lycopersici. During the last two decades there have almost been no progress in the understanding of the molecular mechanisms promoting infection and plant susceptibility. As there are no CRR-resistant lines of cultivated tomato on the market and no other known means for plant protection, a deeper molecular knowledge about the infection process is urgently needed. We have therefore outlined an efficient strategy to search for corky root rot-resistance genes in wild tomato. In addition, we are investigating the genetic determinants for infection and virulence of the fungal pathogen, P. lycopersici. In this review we summarize the quite limited molecular knowledge about the pathogen and the disease, and discuss the possibilities to overcome previous technical obstacles in this new era of molecular biology.

  • 9.
    Gabriëls, Suzan H.E.J
    et al.
    Wageningen University.
    Vossen, Jack, H.
    Wageningen University.
    Ekengren, Sophia, K.
    Stockholm University.
    van Ooijen, Gerben
    University of Amsterdam.
    Abd-El-Haliem, Ahmed. M
    Wageningen University.
    van den Berg, Grardy, C.M.
    Wageningen University.
    Rainey, Daphne, Y.
    Keygene, The Netherlands.
    Martin, Gregory, B.
    BTI, Cornell University.
    Takken, Frank L.W
    University of Amsterdam.
    de Wit, Pierre, J.G.M
    Wageningen University.
    Joosten, Matthieu, H.A.J.
    Wageningen University.
    An NB-LRR protein required for HR signalling mediated by both extra-and intracellular resistance proteins2007In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 50, no 1, p. 14-28Article in journal (Refereed)
    Abstract [en]

    Tomato (Solanum lycopersicum) Cf resistance genes confer hypersensitive response (HR)-associated resistance to strains of the pathogenic fungus Cladosporium fulvum that express the matching avirulence (Avr) gene. Previously, we identified an Avr4-responsive tomato (ART) gene that is required for Cf-4/Avr4-induced HR in Nicotiana benthamiana as demonstrated by virus-induced gene silencing (VIGS). The gene encodes a CC-NB-LRR type resistance (R) protein analogue that we have designated NRC1 (NB-LRR protein required for HR-associated cell death 1). Here we describe that knock-down of NRC1 in tomato not only affects the Cf-4/Avr4-induced HR but also compromises Cf-4-mediated resistance to C. fulvum. In addition, VIGS using NRC1 in N. benthamiana revealed that this protein is also required for the HR induced by the R proteins Cf-9, LeEix, Pto, Rx and Mi. Transient expression of NRC1(D481V), which encodes a constitutively active NRC1 mutant protein, triggers an elicitor-independent HR. Subsequently, we transiently expressed this auto-activating protein in N. benthamiana silenced for genes known to be involved in HR signalling, thereby allowing NRC1 to be positioned in an HR signalling pathway. We found that NRC1 requires RAR1 and SGT1 to be functional, whereas it does not require NDR1 and EDS1. As the Cf-4 protein requires EDS1 for its function, we hypothesize that NRC1 functions downstream of EDS1. We also found that NRC1 acts upstream of a MAP kinase pathway. We conclude that Cf-mediated resistance signalling requires a downstream NB-LRR protein that also functions in cell death signalling pathways triggered by other R proteins.

  • 10.
    Habayeb, Mazen. S.
    et al.
    UCMP, Umeå University.
    Ekengren, Sophia K.
    Stockholm University.
    Hultmark, Dan
    UCMP, Umeå University.
    Nora virus, a persistent virus in Drosophila, defines a new picorna-like virus family2006In: Journal of General Virology, ISSN 0022-1317, E-ISSN 1465-2099, Vol. 87, no 10, p. 3045-3051Article in journal (Refereed)
    Abstract [en]

    Several viruses, including picomaviruses, are known to establish persistent infections, but the mechanisms involved are poorly understood. Here, a novel picoma-like virus, Nora virus, which causes a persistent infection in Drosophila melanogaster, is described. It has a sing le-stranded, positive-sense genomic RNA of 11879 nt, followed by a poly(A) tail. Unlike other picoma-like viruses, the genome has four open reading frames (ORFs). One ORF encodes a picornavirus-like cassette of proteins for virus replication, including an iflavirus-like RNA-dependent RNA polymerase and a helicase that is related to those of mammalian picornaviruses. The three other ORFs are not closely related to any previously described viral sequences. The unusual sequence and genome organization in Nora virus suggest that it belongs to a new family of picorna-like viruses. Surprisingly, Nora virus could be detected in all tested D. melanogaster laboratory stocks, as well as in wild-caught material. The viral titres varied enormously, between 10(4) and 10(10) viral genomes per fly in different stocks, without causing obvious pathological effects. The virus was also found in Drosophila simulans, a close relative of D. melanogaster, but not in more distantly related Drosophila species. It will now be possible to use Drosophila genetics to study the factors that control this persistent infection.

  • 11.
    Hedengren-Olcott, Marika
    et al.
    Oregon State University.
    Olcott, Michael
    Oregon State University.
    Mooney, Duane, T
    Oregon State University.
    Ekengren, Sophia
    Stockholm University.
    Geller, Bruce, L
    Oregon State University.
    Taylor, Barbara, J.
    Oregon State University.
    Differential Activation of the NF-κB-like Factors Relish and Dif in Drosophila melanogaster by Fungi and Gram-positive Bacteria2004In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 279, p. 21121-21127Article in journal (Refereed)
    Abstract [en]

    The current model of immune activation in Drosophila melanogaster suggests that fungi and Gram-positive (G(+)) bacteria activate the Toll/Dif pathway and that Gram-negative (G(-)) bacteria activate the Imd/Relish pathway. To test this model, we examined the response of Relish and Dif (Dorsal-related immunity factor) mutants to challenge by various fungi and G(+) and G(-) bacteria. In Relish mutants, the Cecropin A gene was induced by the G(+) bacteria Micrococcus luteus and Staphylococcus aureus, but not by other G(+) or G(-) bacteria. This Relish-independent Cecropin A induction was blocked in Dif/Relish double mutant flies. Induction of the Cecropin A1 gene by M. luteus required Relish, whereas induction of the Cecropin A2 gene required Dif. Intact peptidoglycan (PG) was necessary for this differential induction of Cecropin A. PG extracted from M. luteus induced Cecropin A in Relish mutants, whereas PGs from the G(+) bacteria Bacillus megaterium and Bacillus subtilis did not, suggesting that the Drosophila immune system can distinguish PGs from various G(+) bacteria. Various fungi stimulated antimicrobial peptides through at least two different pathways requiring Relish and/or Dif. Induction of Attacin A by Geotrichum candidum required Relish, whereas activation by Beauvaria bassiana required Dif, suggesting that the Drosophila immune system can distinguish between at least these two fungi. We conclude that the Drosophila immune system is more complex than the current model. We propose a new model to account for this immune system complexity, incorporating distinct pattern recognition receptors of the Drosophila immune system, which can distinguish between various fungi and G(+) bacteria, thereby leading to selective induction of antimicrobial peptides via differential activation of Relish and Dif.

  • 12.
    Mayrose, Maya
    et al.
    Department of Plant Sciences, Tel Aviv University.
    Ekengren, Sophia
    BTI, Cornell University, USA.
    Melech-Bonfil, Shiri
    Department of Plant Sciences, Tel Aviv University.
    Martin, Gregory B.
    BTI, Cornell University, USA.
    Sessa, Guido
    Department of Plant Sciences, Tel Aviv University.
    A novel link between tomato GRAS genes, plant disease resistance and mechanical stress response2006In: Molecular plant pathology, ISSN 1464-6722, E-ISSN 1364-3703, Vol. 7, no 6, p. 593-604Article in journal (Refereed)
    Abstract [en]

    Members of the GRAS family of transcriptional regulators have been implicated in the control of plant growth and development, and in the interaction of plants with symbiotic bacteria. Here we examine the complexity of the GRAS gene family in tomato (Solanum lycopersicum) and investigate its role in disease resistance and mechanical stress. A large number of tomato ESTs corresponding to GRAS transcripts were retrieved from the public database and assembled in 17 contigs of putative genes. Expression analysis of these genes by real-time RT-PCR revealed that six SlGRAS transcripts accumulate during the onset of disease resistance to Pseudomonas syringae pv. tomato. Further analysis of two selected family members showed that their transcripts preferentially accumulate in tomato plants in response to different avirulent bacteria or to the fungal elicitor EIX, and their expression kinetics correlate with the appearance of the hypersensitive response. In addition, transcript levels of eight SlGRAS genes, including all the Pseudomonas-inducible family members, increased in response to mechanical stress much earlier than upon pathogen attack. Accumulation of SlGRAS transcripts following mechanical stress was in part dependent on the signalling molecule jasmonic acid. Remarkably, suppression of SlGRAS6 gene expression by virus-induced gene silencing impaired tomato resistance to P. syringae pv. tomato. These results support a function for GRAS transcriptional regulators in the plant response to biotic and abiotic stress.

  • 13. Nilsson, Anders K.
    et al.
    Johansson, Oskar N.
    Fahlberg, Per
    Kommuri, Murali
    Topel, Mats
    Bodin, Lovisa J.
    Sikora, Per
    Modarres, Masoomeh
    Ekengren, Sophia
    KTH, School of Biotechnology (BIO), Glycoscience.
    Nguyen, Chi T.
    Farmer, Edward E.
    Olsson, Olof
    Ellerstrom, Mats
    Andersson, Mats X.
    Acylated monogalactosyl diacylglycerol: prevalence in the plant kingdom and identification of an enzyme catalyzing galactolipid head group acylation in Arabidopsis thaliana2015In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 84, no 6, p. 1152-1166Article in journal (Refereed)
    Abstract [en]

    The lipid phase of the thylakoid membrane is mainly composed of the galactolipids mono-and digalactosyl diacylglycerol (MGDG and DGDG, respectively). It has been known since the late 1960s that MGDG can be acylated with a third fatty acid to the galactose head group (acyl-MGDG) in plant leaf homogenates. In certain brassicaceous plants like Arabidopsis thaliana, the acyl-MGDG frequently incorporates oxidized fatty acids in the form of the jasmonic acid precursor 12-oxo-phytodienoic acid (OPDA). In the present study we further investigated the distribution of acylated and OPDA-containing galactolipids in the plant kingdom. While acyl-MGDG was found to be ubiquitous in green tissue of plants ranging from non-vascular plants to angiosperms, OPDA-containing galactolipids were only present in plants from a few genera. A candidate protein responsible for the acyl transfer was identified in Avena sativa (oat) leaf tissue using biochemical fractionation and proteomics. Knockout of the orthologous gene in A. thaliana resulted in an almost total elimination of the ability to form both non-oxidized and OPDA-containing acyl-MGDG. In addition, heterologous expression of the A. thaliana gene in E. coli demonstrated that the protein catalyzed acylation of MGDG. We thus demonstrate that a phylogenetically conserved enzyme is responsible for the accumulation of acyl-MGDG in A. thaliana. The activity of this enzyme in vivo is strongly enhanced by freezing damage and the hypersensitive response.

  • 14.
    Vossen, Jack, H.
    et al.
    Wageningen University.
    Abd-El-Haliem, Ahmed
    Wageningen University.
    Fradin, Emelie, F.
    Wageningen University.
    van den Berg, Grardy, C.M
    Wageningen University.
    Ekengren, Sophia
    Stockholm University.
    Meijer, Harold, J.G
    Wageningen University.
    Seifi, Alireza
    Wageningen University.
    Bai, Yuling
    Wageningen University.
    ten Have, Arjen
    Universidad Nacional de mar del Plata.
    Munnik, Teun
    University of Amsterdam.
    Thomma, Bart, P.H.J
    Wageningen University.
    Joosten, Matthieu, H.A.J
    Wageningen University.
    Identification of tomato phosphatidylinositol-specific phospholipase-C (PI-PLC) family members and the role of PLC4 and PLC6 in HR and disease resistance2010In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 62, no 2, p. 224-239Article in journal (Refereed)
    Abstract [en]

    The perception of pathogen-derived elicitors by plants has been suggested to involve phosphatidylinositol-specific phospholipase-C (PI-PLC) signalling. Here we show that PLC isoforms are required for the hypersensitive response (HR) and disease resistance. We characterised the tomato [Solanum lycopersicum (Sl)] PLC gene family. Six Sl PLC-encoding cDNAs were isolated and their expression in response to infection with the pathogenic fungus Cladosporium fulvum was studied. We found significant regulation at the transcriptional level of the various SlPLCs, and SlPLC4 and SlPLC6 showed distinct expression patterns in C. fulvum-resistant Cf-4 tomato. We produced the encoded proteins in Escherichia coli and found that both genes encode catalytically active PI-PLCs. To test the requirement of these Sl PLCs for full Cf-4-mediated recognition of the effector Avr4, we knocked down the expression of the encoding genes by virus-induced gene silencing. Silencing of SlPLC4 impaired the Avr4/Cf-4-induced HR and resulted in increased colonisation of Cf-4 plants by C. fulvum expressing Avr4. Furthermore, expression of the gene in Nicotiana benthamiana enhanced the Avr4/Cf-4-induced HR. Silencing of SlPLC6 did not affect HR, whereas it caused increased colonisation of Cf-4 plants by the fungus. Interestingly, Sl PLC6, but not Sl PLC4, was also required for resistance to Verticillium dahliae, mediated by the transmembrane Ve1 resistance protein, and to Pseudomonas syringae, mediated by the intracellular Pto/Prf resistance protein couple. We conclude that there is a differential requirement of PLC isoforms for the plant immune response and that Sl PLC4 is specifically required for Cf-4 function, while Sl PLC6 may be a more general component of resistance protein signalling.

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