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W2023494247 abstract "Plants are continuously exposed to attack by potential phytopathogens. Disease prevention requires pathogen recognition and the induction of a multifaceted defense response. We are studying the non-host disease resistance response of parsley to the oomycete, Phytophthora sojae using a cell culture-based system. Receptor-mediated recognition of P. sojae may be achieved through a thirteen amino acid peptide sequence (Pep-13) present within an abundant cell wall transglutaminase. Following recognition of this elicitor molecule, parsley cells mount a defense response, which includes the generation of reactive oxygen species (ROS) and transcriptional activation of genes encoding pathogenesis-related (PR) proteins or enzymes involved in the synthesis of antimicrobial phytoalexins. Treatment of parsley cells with the NADPH oxidase inhibitor, diphenylene iodonium (DPI), blocked both Pep-13-induced phytoalexin production and the accumulation of transcripts encoding enzymes involved in their synthesis. In contrast, DPI treatment had no effect upon Pep-13-induced PRgene expression, suggesting the existence of an oxidative burst-independent mechanism for the transcriptional activation ofPR genes. The use of specific antibodies enabled the identification of three parsley mitogen-activated protein kinases (MAPKs) that are activated within the signal transduction pathway(s) triggered following recognition of Pep-13. Other environmental challenges failed to activate these kinases in parsley cells, suggesting that their activation plays a key role in defense signal transduction. Moreover, by making use of a protoplast co-transfection system overexpressing wild-type and loss-of-function MAPK mutants, we show an essential role for post-translational phosphorylation and activation of MAPKs for oxidative burst-independentPR promoter activation. Plants are continuously exposed to attack by potential phytopathogens. Disease prevention requires pathogen recognition and the induction of a multifaceted defense response. We are studying the non-host disease resistance response of parsley to the oomycete, Phytophthora sojae using a cell culture-based system. Receptor-mediated recognition of P. sojae may be achieved through a thirteen amino acid peptide sequence (Pep-13) present within an abundant cell wall transglutaminase. Following recognition of this elicitor molecule, parsley cells mount a defense response, which includes the generation of reactive oxygen species (ROS) and transcriptional activation of genes encoding pathogenesis-related (PR) proteins or enzymes involved in the synthesis of antimicrobial phytoalexins. Treatment of parsley cells with the NADPH oxidase inhibitor, diphenylene iodonium (DPI), blocked both Pep-13-induced phytoalexin production and the accumulation of transcripts encoding enzymes involved in their synthesis. In contrast, DPI treatment had no effect upon Pep-13-induced PRgene expression, suggesting the existence of an oxidative burst-independent mechanism for the transcriptional activation ofPR genes. The use of specific antibodies enabled the identification of three parsley mitogen-activated protein kinases (MAPKs) that are activated within the signal transduction pathway(s) triggered following recognition of Pep-13. Other environmental challenges failed to activate these kinases in parsley cells, suggesting that their activation plays a key role in defense signal transduction. Moreover, by making use of a protoplast co-transfection system overexpressing wild-type and loss-of-function MAPK mutants, we show an essential role for post-translational phosphorylation and activation of MAPKs for oxidative burst-independentPR promoter activation. reactive oxygen species pathogenesis-related mitogen-activated protein kinase glutathione S-transferase β-glucuronidase luciferase N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine myelin basic protein diphenylene iodonium dimethyl sulfoxide S-adenosyl-l-methionine:bergaptolO-methyltransferase elicitor-responsive MAPK 4-D,2,4-dichlorophenoxy acetic acid In most circumstances plants are able to defend themselves against pathogen attack. This is primarily facilitated through recognition mechanisms, which plants use to sense the presence of the pathogen (1Nürnberger T. Brunner F. Curr. Opin. Plant Biol. 2002; 5: 318-324Crossref PubMed Scopus (288) Google Scholar, 2Dangl J.L. Jones J.D.G. Nature. 2001; 411: 826-833Crossref PubMed Scopus (2927) Google Scholar, 3Nürnberger T. Scheel D. Trends Plant Sci. 2001; 6: 372-379Abstract Full Text Full Text PDF PubMed Scopus (246) Google Scholar), and through triggering intrinsic defense mechanisms that either kill the pathogen or limit its spread to the site of immediate infection (4Scheel D. Curr. Opin. Plant Biol. 1998; 1: 305-310Crossref PubMed Scopus (221) Google Scholar, 5Heath M.C. Curr. Opin. Plant Biol. 2000; 3: 315-319Crossref PubMed Scopus (440) Google Scholar). Parsley (Petroselinum crispum) exhibits a non-host resistance response to attack by the oomycetes,Phytophthora infestans and Phytophthora sojae (6Kamoun S. Curr. Opin. Plant Biol. 2001; 4: 295-300Crossref PubMed Scopus (123) Google Scholar,7Jahnen W. Hahlbrock K. Planta. 1988; 173: 197-204Crossref PubMed Scopus (82) Google Scholar). Defense reactions are triggered through the recognition of an abundant cell wall transglutaminase present and conserved in all but one tested member of Phytophthora (8Brunner F. Rosahl S. Lee J. Rudd J.J. Geiler C. Kauppinen S. Rasmussen G. Scheel D. Nürnberger T. EMBO J. 2002; 21: 6681-6688Crossref PubMed Scopus (218) Google Scholar). This protein was previously characterized as a 42-kDa glycoprotein purified fromP. sojae that was able to trigger phytoalexin accumulation when added to cultured parsley cells (9Sacks W.R. Nürnberger T. Hahlbrock K. Scheel D. Mol. Gen. Genet. 1995; 246: 45-55Crossref PubMed Scopus (51) Google Scholar, 10Parker J.E. Schulte W. Hahlbrock K. Scheel D. Mol. Plant-Microbe Interact. 1991; 4: 19-27Crossref Google Scholar). Within this protein resides a conserved peptide sequence of 13 amino acids (Pep-13) that is necessary and sufficient for its elicitor activity (11Nürnberger T. Nennstiel D. Jabs T. Sacks W.R. Hahlbrock K. Scheel D. Cell. 1994; 78: 449-460Abstract Full Text PDF PubMed Scopus (465) Google Scholar). The ability of Pep-13 to trigger defense responses in parsley requires its interaction with a 100-kDa receptor protein present in the plasma membrane of parsley cells (12Nürnberger T. Nennstiel D. Hahlbrock K. Scheel D. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 2338-2342Crossref PubMed Scopus (54) Google Scholar, 13Nennstiel D. Scheel D. Nürnberger T. FEBS Lett. 1998; 431: 405-410Crossref PubMed Scopus (43) Google Scholar), since all mutations made within the Pep-13 sequence that prevented binding to the receptor also inhibited the elicitation of defense reactions (11Nürnberger T. Nennstiel D. Jabs T. Sacks W.R. Hahlbrock K. Scheel D. Cell. 1994; 78: 449-460Abstract Full Text PDF PubMed Scopus (465) Google Scholar, 14Blume B. Nürnberger T. Nass N. Scheel D. Plant Cell. 2000; 12: 1425-1440Crossref PubMed Scopus (339) Google Scholar, 15Jabs T. Tschöpe M. Colling C. Hahlbrock K. Scheel D. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 4800-4805Crossref PubMed Scopus (496) Google Scholar, 16Ligterink W. Kroj T. zur Nieden U. Hirt H. Scheel D. Science. 1997; 276: 2054-2057Crossref PubMed Scopus (314) Google Scholar, 17Zimmermann S. Nürnberger T. Frachisse J.-M. Wirtz W. Guern J. Hedrich R. Scheel D. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 2751-2755Crossref PubMed Scopus (182) Google Scholar). The defense response itself is multifaceted and involves the generation of reactive oxygen species (ROS)1 (15Jabs T. Tschöpe M. Colling C. Hahlbrock K. Scheel D. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 4800-4805Crossref PubMed Scopus (496) Google Scholar), the synthesis of antimicrobial furanocoumarin phytoalexins (10Parker J.E. Schulte W. Hahlbrock K. Scheel D. Mol. Plant-Microbe Interact. 1991; 4: 19-27Crossref Google Scholar), and the expression of defense-related genes including pathogenesis-related (PR) genes (18Somssich I.E. Bollmann J. Hahlbrock K. Kombrink E. Schulz W. Plant Mol. Biol. 1989; 12: 227-234Crossref PubMed Scopus (98) Google Scholar). Pep-13-induced defense gene activation is temporally regulated (18Somssich I.E. Bollmann J. Hahlbrock K. Kombrink E. Schulz W. Plant Mol. Biol. 1989; 12: 227-234Crossref PubMed Scopus (98) Google Scholar). Transcripts of immediate early genes, including the WRKY1, -3, -4, and –5 transcription factor genes, accumulate rapidly after elicitation apparently without the requirement of de novoprotein synthesis (19Cormack R.S. Eulgem T. Rushton P.J. Köchner P. Hahlbrock K. Somssich I.E. Biochim. Biophys. Acta. 2002; 1576: 92-100Crossref PubMed Scopus (94) Google Scholar). With a slight delay, transient activation of another group of early genes is observed, among these are thePR1 and PR2 genes (18Somssich I.E. Bollmann J. Hahlbrock K. Kombrink E. Schulz W. Plant Mol. Biol. 1989; 12: 227-234Crossref PubMed Scopus (98) Google Scholar, 20Batz O. Logemann E. Reinold S. Hahlbrock K. Biol. Chem. 1998; 379: 1127-1135Crossref PubMed Scopus (59) Google Scholar, 21Eulgem T. Rushton P.J. Schmelzer E. Hahlbrock K. Somssich I.E. EMBO J. 1999; 18: 4689-4699Crossref PubMed Scopus (448) Google Scholar). ManyPR-type defense-related genes appear to be regulated by WRKY transcription factors (22Eulgem T. Rushton P.J. Robatzek S. Somssich I.E. Trends Plant Sci. 2000; 5: 199-206Abstract Full Text Full Text PDF PubMed Scopus (2035) Google Scholar, 23Rushton P.J. Somssich I.E. Curr. Opin. Plant Biol. 1998; 1: 311-315Crossref PubMed Scopus (311) Google Scholar), which have been analyzed in particular for the parsley PR1 promoter (21Eulgem T. Rushton P.J. Schmelzer E. Hahlbrock K. Somssich I.E. EMBO J. 1999; 18: 4689-4699Crossref PubMed Scopus (448) Google Scholar, 24Rushton P.J. Torres J.T. Parniske M. Wernert P. Hahlbrock K. Somssich I.E. EMBO J. 1996; 15: 5690-5700Crossref PubMed Scopus (534) Google Scholar). Transcripts encoding enzymes implicated in phenylpropanoid metabolism and the synthesis of the furanocoumarin phytoalexins, including phenylalanine ammonia-lyase (PAL), 4-coumarate:CoA ligase (4CL), andS-adenosyl-l-methionine:bergaptolO-methyltransferase (BMT) accumulate even later (20Batz O. Logemann E. Reinold S. Hahlbrock K. Biol. Chem. 1998; 379: 1127-1135Crossref PubMed Scopus (59) Google Scholar). Treatment of parsley cells with diphenylene iodonium chloride (DPI) blocks both the induction of the oxidative burst and phytoalexin biosynthesis by elicited parsley cells (15Jabs T. Tschöpe M. Colling C. Hahlbrock K. Scheel D. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 4800-4805Crossref PubMed Scopus (496) Google Scholar). Moreover, it has been shown that the generation of O2⨪ via the oxidative burst is necessary and sufficient to drive phytoalexin biosynthesis by the cells (15Jabs T. Tschöpe M. Colling C. Hahlbrock K. Scheel D. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 4800-4805Crossref PubMed Scopus (496) Google Scholar). Calcium influx through Pep-13-responsive ion channels of the plasma membrane (15Jabs T. Tschöpe M. Colling C. Hahlbrock K. Scheel D. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 4800-4805Crossref PubMed Scopus (496) Google Scholar, 17Zimmermann S. Nürnberger T. Frachisse J.-M. Wirtz W. Guern J. Hedrich R. Scheel D. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 2751-2755Crossref PubMed Scopus (182) Google Scholar) followed by elevation of cytosolic calcium levels (14Blume B. Nürnberger T. Nass N. Scheel D. Plant Cell. 2000; 12: 1425-1440Crossref PubMed Scopus (339) Google Scholar) were found to be located upstream of the oxidative burst and the activation of a mitogen-activated protein kinase (MAPK) (14Blume B. Nürnberger T. Nass N. Scheel D. Plant Cell. 2000; 12: 1425-1440Crossref PubMed Scopus (339) Google Scholar,16Ligterink W. Kroj T. zur Nieden U. Hirt H. Scheel D. Science. 1997; 276: 2054-2057Crossref PubMed Scopus (314) Google Scholar). The DPI insensitivity of this Pep-13-induced MAPK activation positions this kinase between calcium influx and oxidative burst or indicates bifurcation of the signaling pathway into DPI-sensitive and -insensitive branches (16Ligterink W. Kroj T. zur Nieden U. Hirt H. Scheel D. Science. 1997; 276: 2054-2057Crossref PubMed Scopus (314) Google Scholar).Pharmacological and 32P-labeling studies have long since indicated the importance of protein phosphorylation and protein kinase activities in bringing about pathogen defense responses both in parsley and other systems (25Dietrich A. Mayer J.E. Hahlbrock K. J. Biol. Chem. 1990; 265: 6360-6368Abstract Full Text PDF PubMed Google Scholar, 26Felix G. Grosskopf D.G. Regenass M. Boller T. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 8831-8834Crossref PubMed Scopus (215) Google Scholar). Among the many implicated protein kinases, the activation of MAPKs has been shown to be a consistent and common response of plant cells following infection and exposure to microbial elicitors (27Zhang S. Klessig D.F. Trends Plant Sci. 2001; 6: 520-527Abstract Full Text Full Text PDF PubMed Scopus (582) Google Scholar, 28Romeis T. Curr. Opin. Plant Biol. 2001; 4: 407-414Crossref PubMed Scopus (178) Google Scholar). Based upon analysis of the fully sequencedArabidopsis thaliana genome, plants appear to contain more putative MAPKs than any other known organism, including humans (29The Arabidopsis Genome Initiative Nature. 2000; 408: 796-815Crossref PubMed Scopus (7056) Google Scholar).Arabidopsis possesses at least 20 MAPK-encoding genes that fall into a minimum of four subgroups (30Tena G. Asai T. Chiu W.-L. Sheen J. Curr. Opin. Plant Biol. 2001; 4: 392-400Crossref PubMed Scopus (397) Google Scholar, 31Ichimura K. Tena G. Henry Y. Zhang S. Hirt H. Ellis B.E. Morris P.C. Wilson C. Champion A. Innes R.W. Sheen J. Ecker J.R. Scheel D. Klessig D.F. Machida Y. Mundy J. Ohashi Y. Kreis M. Heberle-Bors E. Walker J.C. Shinozaki K. Trends Plant Sci. 2002; 7: 301-308Abstract Full Text Full Text PDF PubMed Scopus (916) Google Scholar). In all systems whereby MAPK activity has been studied with respect to elicitor responses, activation of members of the AtMPK6 subgroup has been described (1Nürnberger T. Brunner F. Curr. Opin. Plant Biol. 2002; 5: 318-324Crossref PubMed Scopus (288) Google Scholar,27Zhang S. Klessig D.F. Trends Plant Sci. 2001; 6: 520-527Abstract Full Text Full Text PDF PubMed Scopus (582) Google Scholar). This includes the responses of tobacco SIPK to general elicitors, such as Harpin and elicitins, TMV infection, and race-specific elicitation (32Droillard M.J. Thibivilliers S. Cazale A.C. Barbier-Brygoo H. Lauriere C. FEBS Lett. 2000; 474: 217-222Crossref PubMed Scopus (59) Google Scholar, 33Lee J. Klessig D.F. Nürnberger T. Plant Cell. 2001; 13: 1079-1093Crossref PubMed Scopus (192) Google Scholar, 34Romeis T. Piedras P. Zhang S. Klessig D.F. Hirt H. Jones J.D. Plant Cell. 1999; 11: 273-287PubMed Google Scholar, 35Zhang S. Klessig D.F. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 7433-7438Crossref PubMed Scopus (231) Google Scholar, 36Zhang S., Du, H. Klessig D.F. Plant Cell. 1998; 10: 435-449PubMed Google Scholar); alfalfa SIMK to chitin, ergosterol, and β-glucans (37Cardinale F. Jonak C. Ligterink W. Niehaus K. Boller T. Hirt H. J. Biol. Chem. 2000; 275: 36734-36740Abstract Full Text Full Text PDF PubMed Scopus (124) Google Scholar); A. thaliana AtMPK6 to bacterial elicitors including the flg22 peptide from flagellin (38Nühse T.S. Peck S.C. Hirt H. Boller T. J. Biol. Chem. 2000; 275: 7521-7526Abstract Full Text Full Text PDF PubMed Scopus (245) Google Scholar) and Harpin (39Desikan R. Clarke A. Atherfold P. Hancock J.T. Neill S.J. Planta. 1999; 210: 97-103Crossref PubMed Scopus (54) Google Scholar). It was recently demonstrated for A. thaliana that MAPKs can also act as negative regulators of defense responses, as shown for AtMPK4 mutants (40Petersen M. Brodersen P. Naested H. Andreasson E. Lindhart U. Johansen B. Nielsen H.B. Lacy M. Austin M.J. Parker J.E. Sharma S.B. Klessig D.F. Martienssen R. Mattson O. Jensen A.B. Mundy J. Cell. 2000; 103: 1111-1120Abstract Full Text Full Text PDF PubMed Scopus (770) Google Scholar); however, this would appear to be contradictory to the activation of this kinase described in response to Harpin (39Desikan R. Clarke A. Atherfold P. Hancock J.T. Neill S.J. Planta. 1999; 210: 97-103Crossref PubMed Scopus (54) Google Scholar). Members of a second closely related class of MAPKs, initially characterized in tobacco as being activated following wounding (WIPK) (41Seo S. Okamoto M. Seto H. Ishizuka K. Sano H. Ohashi Y. Science. 1995; 270: 1988-1992Crossref PubMed Scopus (465) Google Scholar, 42Bögre L. Ligterink W. Meskiene I. Baker P. Heberle-Bors E. Hirt H. Plant Cell. 1997; 9: 75-83Crossref PubMed Scopus (192) Google Scholar), and having homology to AtMPK3, have also been implicated in pathogen defense signaling (34Romeis T. Piedras P. Zhang S. Klessig D.F. Hirt H. Jones J.D. Plant Cell. 1999; 11: 273-287PubMed Google Scholar, 43Zhang S. Klessig D.F. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 7225-7230Crossref PubMed Scopus (193) Google Scholar, 44Zhang S. Liu Y. Klessig D.F. Plant J. 2000; 23: 1-9Crossref PubMed Google Scholar). Our previous studies demonstrated the activation of such a homologue, described as ERM kinase, following treatment of parsley cells with the Pep-13 elicitor (16Ligterink W. Kroj T. zur Nieden U. Hirt H. Scheel D. Science. 1997; 276: 2054-2057Crossref PubMed Scopus (314) Google Scholar).Evidence indicating the importance of MAPK activation for the elicitation of defense reactions has recently emerged from gain-of-function experiments whereby MAPKs themselves, or constitutively active forms of their upstream activators, MAPK kinases (MAPKKs), were transiently overexpressed in tobacco andArabidopsis leaves (45Ren D. Yang H. Zhang S. J. Biol. Chem. 2002; 277: 559-565Abstract Full Text Full Text PDF PubMed Scopus (343) Google Scholar, 46Yang K.-Y. Liu Y. Zhang S. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 741-746Crossref PubMed Scopus (398) Google Scholar, 47Zhang S. Liu Y. Plant Cell. 2001; 13: 1877-1889Crossref PubMed Scopus (161) Google Scholar). This resulted in a hypersensitive response-type phenotype in leaves in addition to activation of genes implicated in the biosynthesis of defense-related antimicrobial compounds. These observations have recently been supported by the identification of a complete MAPK cascade fromA. thaliana that is triggered through recognition of flg22 (48Asai T. Tena G. Plotnikova J. Willmann M.R. Chiu W.-L. Gomez-Gomez L. Boller T. Ausubel F.M. Sheen J. Nature. 2002; 415: 977-983Crossref PubMed Scopus (1954) Google Scholar). This resulted not only in the accumulation of transcripts of a group of defense-related genes, but also in increased resistance to attack by both fungal and bacterial pathogens (48Asai T. Tena G. Plotnikova J. Willmann M.R. Chiu W.-L. Gomez-Gomez L. Boller T. Ausubel F.M. Sheen J. Nature. 2002; 415: 977-983Crossref PubMed Scopus (1954) Google Scholar). In addition to these functions in defense, AtMPK6 homologues have been shown to be activated in response to various abiotic stresses including osmotic stresses, ozone exposure, oxidative stress, cold stress, drought, and treatment with salicylic acid (32Droillard M.J. Thibivilliers S. Cazale A.C. Barbier-Brygoo H. Lauriere C. FEBS Lett. 2000; 474: 217-222Crossref PubMed Scopus (59) Google Scholar, 49Cazale A.C. Droillard M.J. Wilson C. Heberle-Bors E. Barbier-Brygoo H. Lauriere C. Plant J. 1999; 19: 297-307Crossref PubMed Scopus (55) Google Scholar, 50Hoyos E. Zhang S. Plant Physiol. 2000; 122: 1355-1363Crossref PubMed Scopus (106) Google Scholar, 51Kovtun Y. Chiu W.-L. Tena G. Sheen J. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 2940-2945Crossref PubMed Scopus (1163) Google Scholar, 52Munnik T. Ligterink W. Meskiene I. Calderini O. Beyerly J. Musgrave A. Hirt H. Plant J. 1999; 20: 381-388Crossref PubMed Google Scholar, 53Mikolajczyk M. Awotunde O.S. Muszynska G. Klessig D.F. Dobrowolska G. Plant Cell. 2000; 12: 165-178Crossref PubMed Scopus (252) Google Scholar, 54Zhang S. Klessig D.F. Plant Cell. 1997; 9: 809-824Crossref PubMed Scopus (462) Google Scholar, 55Jonak C. Kiegerl S. Ligterink W. Barker P.J. Neville S.H. Hirt H. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 11274-11279Crossref PubMed Scopus (390) Google Scholar, 56Ichimura K. Mizoguchi T. Yoshida R. Yuasa T. Shinozaki K. Plant J. 2000; 24: 655-665Crossref PubMed Google Scholar, 57Samuel M.A. Miles G.P. Ellis B.E. Plant J. 2000; 22: 367-376Crossref PubMed Google Scholar, 58Yuasa T. Ichimura K. Mizoguchi T. Shinozaki K. Plant Cell Physiol. 2001; 42: 1012-1016Crossref PubMed Scopus (136) Google Scholar). It has therefore been suggested that members of this class of MAPKs may function as points of cross-talk between various stress signaling pathways in plants (3Nürnberger T. Scheel D. Trends Plant Sci. 2001; 6: 372-379Abstract Full Text Full Text PDF PubMed Scopus (246) Google Scholar, 27Zhang S. Klessig D.F. Trends Plant Sci. 2001; 6: 520-527Abstract Full Text Full Text PDF PubMed Scopus (582) Google Scholar,30Tena G. Asai T. Chiu W.-L. Sheen J. Curr. Opin. Plant Biol. 2001; 4: 392-400Crossref PubMed Scopus (397) Google Scholar).In this article we demonstrate the existence of parallel pathways that operate to induce the transcriptional activation of particular sets of defense-related genes in parsley. One pathway is triggered downstream of the oxidative burst and controls genes implicated in phytoalexin biosynthesis. The second pathway is independent of the oxidative burst, but is dependent on MAPK activity. The MAPKs involved are activated in parsley cells through receptor-mediated recognition of the Pep-13 elicitor and other elicitors of defense reactions, but appear largely insensitive to abiotic stresses, suggesting that their activation is primarily associated with pathogen defense. Furthermore, by utilizing a protoplast transient transfection system employing loss-of-function MAPK mutants, we demonstrate a requirement of MAPK activity for the elicitor-mediated oxidative burst-independent activation ofPR genes, which represent classical markers for pathogen defense responses in plants.DISCUSSIONReceptor-mediated perception of plant pathogens results in the activation of intracellular signaling pathways that function in triggering downstream defense reactions (3Nürnberger T. Scheel D. Trends Plant Sci. 2001; 6: 372-379Abstract Full Text Full Text PDF PubMed Scopus (246) Google Scholar, 4Scheel D. Curr. Opin. Plant Biol. 1998; 1: 305-310Crossref PubMed Scopus (221) Google Scholar). Defense reactions themselves are characterized by large-scale transcriptional activation of genes, whose products are believed to be actively involved in resisting pathogen attack (20Batz O. Logemann E. Reinold S. Hahlbrock K. Biol. Chem. 1998; 379: 1127-1135Crossref PubMed Scopus (59) Google Scholar, 71Glazebrook J. Curr. Opin. Plant Biol. 2001; 4: 301-308Crossref PubMed Scopus (570) Google Scholar). Our studies have demonstrated that particular signaling pathways are responsible for the transcriptional activation of distinct subsets of defense genes. It is clear that both oxidative burst-dependent and -independent pathways play roles in this response. Previous studies, and those presented here, have demonstrated that the generation of O2⨪, most likely through the activity of an NADPH oxidase homologue(s), is necessary and sufficient to drive the synthesis of antimicrobial phytoalexins in parsley cells (15Jabs T. Tschöpe M. Colling C. Hahlbrock K. Scheel D. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 4800-4805Crossref PubMed Scopus (496) Google Scholar). The use in these studies of the NADPH oxidase inhibitor, DPI, to block Pep-13-induced phytoalexin biosynthesis, correlated with its ability to inhibit the transcript accumulation of genes encoding enzymes involved in this process. The transcriptional activation of these genes belongs to the late reactions of elicited parsley cells (18Somssich I.E. Bollmann J. Hahlbrock K. Kombrink E. Schulz W. Plant Mol. Biol. 1989; 12: 227-234Crossref PubMed Scopus (98) Google Scholar, 20Batz O. Logemann E. Reinold S. Hahlbrock K. Biol. Chem. 1998; 379: 1127-1135Crossref PubMed Scopus (59) Google Scholar). In contrast, transcript accumulation of genes involved in the immediate early and early reactions (21Eulgem T. Rushton P.J. Schmelzer E. Hahlbrock K. Somssich I.E. EMBO J. 1999; 18: 4689-4699Crossref PubMed Scopus (448) Google Scholar, 23Rushton P.J. Somssich I.E. Curr. Opin. Plant Biol. 1998; 1: 311-315Crossref PubMed Scopus (311) Google Scholar) was unaffected by this treatment suggesting that a separate, albeit parallel, oxidative burst-independent pathway controls the transcriptional activation of such genes.Changes in protein phosphorylation have long been known to occur as a consequence of treatment of plant cells with microbial elicitors (25Dietrich A. Mayer J.E. Hahlbrock K. J. Biol. Chem. 1990; 265: 6360-6368Abstract Full Text PDF PubMed Google Scholar,26Felix G. Grosskopf D.G. Regenass M. Boller T. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 8831-8834Crossref PubMed Scopus (215) Google Scholar). Among the many protein kinases believed to be involved in these events, members of the MAPK family are becoming increasingly recognized as playing important roles in defense signaling (27Zhang S. Klessig D.F. Trends Plant Sci. 2001; 6: 520-527Abstract Full Text Full Text PDF PubMed Scopus (582) Google Scholar, 28Romeis T. Curr. Opin. Plant Biol. 2001; 4: 407-414Crossref PubMed Scopus (178) Google Scholar). In the present study we have shown that in parsley cells at least four different MAPKs are activated in a receptor-dependent manner by the Phytophthora-derived elicitor peptide, Pep-13. Three of these MAPKs could be identified by molecular cloning, immunoprecipitation, and transient transformation assays, and they were found to be homologous to MAPKs implicated in defense signaling in other plant species (3Nürnberger T. Scheel D. Trends Plant Sci. 2001; 6: 372-379Abstract Full Text Full Text PDF PubMed Scopus (246) Google Scholar, 27Zhang S. Klessig D.F. Trends Plant Sci. 2001; 6: 520-527Abstract Full Text Full Text PDF PubMed Scopus (582) Google Scholar, 31Ichimura K. Tena G. Henry Y. Zhang S. Hirt H. Ellis B.E. Morris P.C. Wilson C. Champion A. Innes R.W. Sheen J. Ecker J.R. Scheel D. Klessig D.F. Machida Y. Mundy J. Ohashi Y. Kreis M. Heberle-Bors E. Walker J.C. Shinozaki K. Trends Plant Sci. 2002; 7: 301-308Abstract Full Text Full Text PDF PubMed Scopus (916) Google Scholar, 48Asai T. Tena G. Plotnikova J. Willmann M.R. Chiu W.-L. Gomez-Gomez L. Boller T. Ausubel F.M. Sheen J. Nature. 2002; 415: 977-983Crossref PubMed Scopus (1954) Google Scholar). The initial in-gel and Western blotting experiments also suggest that at least one elicitor-responsive MAPK remains to be identified. Based upon the activation profile seen for each of the kinases with these methods, and compared with the activities determined through specific immunoprecipitation/kinase assays, this remaining kinase would appear to be activated more transiently than the PcMPK6 and PcMPK3 kinases. Given the lack of any cross-reacting antisera we have as yet been unable to identify this additional activity.The MAPKs we have identified as Pep-13-responsive have homology to those seen to be implicated in elicitor signaling in other systems,i.e. homologues of the AtMPK6 and AtMPK3 MAPKs fromArabidopsis (27Zhang S. Klessig D.F. Trends Plant Sci. 2001; 6: 520-527Abstract Full Text Full Text PDF PubMed Scopus (582) Google Scholar). In addition, we isolated a parsley homologue of AtMPK4, a MAPK shown to be a negative regulator of disease-resistance responses in Arabidopsis (40Petersen M. Brodersen P. Naested H. Andreasson E. Lindhart U. Johansen B. Nielsen H.B. Lacy M. Austin M.J. Parker J.E. Sharma S.B. Klessig D.F. Martienssen R. Mattson O. Jensen A.B. Mundy J. Cell. 2000; 103: 1111-1120Abstract Full Text Full Text PDF PubMed Scopus (770) Google Scholar). This MAPK was not responsive to elicitors (Pep-13 or HrpZ) in parsley cells, and we cannot say whether it is functionally homologous to theArabidopsis MAP kinase 4, which was previously described as being activated in response to Harpin treatments (39Desikan R. Clarke A. Atherfold P. Hancock J.T. Neill S.J. Planta. 1999; 210: 97-103Crossref PubMed Scopus (54) Google Scholar). We also isolated two parsley MAPKs belonging to the AtMPK3 class and have shown that both become activated following Pep-13 treatment. Whether these two kinases share a common function remains to be determined. One might suppose that they could have, despite their high degree of sequence identity, slight differences with respect to substrate specificities and interaction with activators and deactivators, or even that their expression profile in planta might differ. InArabidopsis quite a number of such highly homologous MAPK pairs have been identified (29The Arabidopsis Genome Initiative Nature. 2000; 408: 796-815Crossref PubMed Scopus (7056) Google Scholar, 31Ichimura K. Tena G. Henry Y. Zhang S. Hirt H. Ellis B.E. Morris P.C. Wilson C. Champion A. Innes R.W. Sheen J. Ecker J.R. Scheel D. Klessig D.F. Machida Y. Mundy J. Ohashi Y. Kreis M. Heberle-Bors E. Walker J.C. Shinozaki K. Trends Plant Sci. 2002; 7: 301-308Abstract Full Text Full Text PDF PubMed Scopus (916) Google Scholar), and it will be interesting in the future to learn to what extent their functions are redundant.The other Pep-13-responsive MAPK was shown to be PcMPK6, a homologue of the AtMPK6, SIPK, and SIMK MAPKs from Arabidopsis, tobacco, and alfalfa, respectively, each of which has been shown to be activated following elicitation (32Droi" @default.
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W2023494247 title "Mitogen-activated Protein Kinases Play an Essential Role in Oxidative Burst-independent Expression of Pathogenesis-related Genes in Parsley" @default.
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W2023494247 doi "https://doi.org/10.1074/jbc.m208200200" @default.
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