The Arabidopsis Protein Kinase PTI1-2 Is Activated by Convergent Phosphatidic Acid and Oxidative Stress Signaling Pathways Downstream of PDK1 and OXI1

Abstract

Arabidopsis PDK1 activity is regulated by binding to the lipid phosphatidic acid (PA) resulting in activation of the oxidative stress-response protein kinase OXI1/AGC2-1. Thus there is an inferred link between lipid signaling and oxidative stress signaling modules. Among a panel of hormones and stresses tested, we found that, in addition to PA, the fungal elicitor xylanase activated PDK1, suggesting that PDK1 has a role in plant pathogen defense mechanisms. The downstream OXI1 was activated by additional stress factors, including PA, H2O2, and partially by xylanase. We have isolated an interacting partner of OXI1, a Ser/Thr kinase (PTI1-2), which is downstream of OXI1. Its sequence closely resembles the tomato Pti kinase, which has been implicated in the hypersensitive response, a localized programmed cell death that occurs at the site of pathogen infection. PTI1-2 is activated by the same stresses/elicitors as OXI1 and additionally flagellin. We have used RNA interference to knock out the expression of PDK1 and OXI1 and to study the effects on PTI1-2 activity. We show that specific lipid signaling pathways converge on PTI1-2 via the PDK1-OXI1 axis, whereas H2O2 and flagellin signals to OXI1-PTI1-2 via a PDK1-independent pathway. PTI1-2 represents a new downstream component that integrates diverse lipid and reactive oxygen stress signals and functions closely with OXI1. Arabidopsis PDK1 activity is regulated by binding to the lipid phosphatidic acid (PA) resulting in activation of the oxidative stress-response protein kinase OXI1/AGC2-1. Thus there is an inferred link between lipid signaling and oxidative stress signaling modules. Among a panel of hormones and stresses tested, we found that, in addition to PA, the fungal elicitor xylanase activated PDK1, suggesting that PDK1 has a role in plant pathogen defense mechanisms. The downstream OXI1 was activated by additional stress factors, including PA, H2O2, and partially by xylanase. We have isolated an interacting partner of OXI1, a Ser/Thr kinase (PTI1-2), which is downstream of OXI1. Its sequence closely resembles the tomato Pti kinase, which has been implicated in the hypersensitive response, a localized programmed cell death that occurs at the site of pathogen infection. PTI1-2 is activated by the same stresses/elicitors as OXI1 and additionally flagellin. We have used RNA interference to knock out the expression of PDK1 and OXI1 and to study the effects on PTI1-2 activity. We show that specific lipid signaling pathways converge on PTI1-2 via the PDK1-OXI1 axis, whereas H2O2 and flagellin signals to OXI1-PTI1-2 via a PDK1-independent pathway. PTI1-2 represents a new downstream component that integrates diverse lipid and reactive oxygen stress signals and functions closely with OXI1. It is now clear that reactive oxygen species (ROS) 2The abbreviations used are: ROS, reactive oxygen species; PDK1, phosphoinositide-dependent protein kinase 1; PA, phosphatidic acid; OXI1, oxidative signal-inducible 1; PH, pleckstrin homology domain; PIF, PDK1-interacting fragment; PLD, phospholipase D; PLC, phospholipase C; MAPK, mitogen-activated protein kinase; ABA, abscisic acid; HA, hemagglutinin; MBP, myelin basic protein; GST, glutathione S-transferase; RNAi, RNA interference; BisTris, bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane. play an important signaling role in plants controlling processes such as growth, development, programmed cell death, and responses to biotic and abiotic environmental stimuli (1Apel K. Hirt H. Annu. Rev. Plant Biol. 2004; 55: 373-399Crossref PubMed Scopus (8374) Google Scholar). Current evidence supports the concept that ROS represent a significant point of convergence between pathways that respond to biotic and abiotic stresses (2Fujita M. Fujita Y. Noutoshi Y. Takahashi F. Narusaka Y. Yamaguchi-Shinozaki K. Shinozaki K. Curr. Opin. Plant Biol. 2006; 9: 436-442Crossref PubMed Scopus (1391) Google Scholar). Nevertheless, our current understanding of ROS participation in cross-talk between these pathways is very limited (2Fujita M. Fujita Y. Noutoshi Y. Takahashi F. Narusaka Y. Yamaguchi-Shinozaki K. Shinozaki K. Curr. Opin. Plant Biol. 2006; 9: 436-442Crossref PubMed Scopus (1391) Google Scholar). OXI1/AGC2-1 is a protein kinase that was identified as a downstream signaling component to the PDK1 (3-phosphinositide-dependent protein kinase 1) and as a protein kinase that is required for oxidative burst-mediated signaling in Arabidopsis, hereafter referred to as OXI1 (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar, 4Rentel M.C. Lecourieux D. Ouaked F. Usher S.L. Petersen L. Okamoto H. Knight H. Peck S.C. Grierson C.S. Hirt H. Knight M.R. Nature. 2004; 427: 858-861Crossref PubMed Scopus (463) Google Scholar). OXI1 is critical for at least two very different ROS-mediated processes, basal resistance to Peronospora parasitica infection and root hair growth (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar, 4Rentel M.C. Lecourieux D. Ouaked F. Usher S.L. Petersen L. Okamoto H. Knight H. Peck S.C. Grierson C.S. Hirt H. Knight M.R. Nature. 2004; 427: 858-861Crossref PubMed Scopus (463) Google Scholar). OXI1 is a member of the AGC family of protein kinases, and we have reported previously that OXI1 is activated by PDK1-mediated phosphorylation. In addition PDK1 acts upstream of other AGC kinases and regulates diverse signaling pathways, involved in root hair growth, auxin regulation, and plant cell death (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar, 5Zegzouti H. Anthony R.G. Jahchan N. Bogre L. Christensen S.K. Proc. Natl. Acad. Sci. U. S. A. 2006; 103: 6404-6409Crossref PubMed Scopus (95) Google Scholar, 6Devarenne T.P. Ekengren S.K. Pedley K.F. Martin G.B. EMBO J. 2006; 25: 255-265Crossref PubMed Scopus (70) Google Scholar). PDK1 enzyme activity is regulated by binding the lipid signaling molecule, phosphatidic acid (PA), to its pleckstrin homology (PH) domain (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar). PA is produced in response to many different stresses, including absisic acid (ABA)-induced stomatal closure, pathogen attack, and oxidative stress (7Testerink C. Munnik T. Trends Plant Sci. 2005; 10: 368-375Abstract Full Text Full Text PDF PubMed Scopus (462) Google Scholar, 8Wang X. Devaiah S.P. Zhang W. Welti R. Prog. Lipid. Res. 2006; 45: 250-278Crossref PubMed Scopus (578) Google Scholar). It is generated via two distinct phospholipase pathways, either directly by phospholipase D (PLD) or the sequential action of phospholipase C (PLC) and diacylglyerol kinase (7Testerink C. Munnik T. Trends Plant Sci. 2005; 10: 368-375Abstract Full Text Full Text PDF PubMed Scopus (462) Google Scholar). Use of specific inhibitors to PLD and PLC has shown that PDK1 is specifically activated by PLD-generated PA (PAPLD) (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar). The oxidative burst is one of the earliest responses of plants to pathogens, transiently produced in forms, including hydrogen peroxide and superoxide (9Torres M.A. Jones J.D. Dangl J.L. Nat. Genet. 2005; 37: 1130-1134Crossref PubMed Scopus (448) Google Scholar, 10Davies D.R. Bindschedler L.V. Strickland T.S. Bolwell G.P. J. Exp. Bot. 2006; 57: 1817-1827Crossref PubMed Scopus (79) Google Scholar). ROS produced in this way serve not as as signals plant defense including the hypersensitive response of the of either or has been in plant to or such as cell or specific by the pathogen T. A. A. G. T. Munnik T. Plant PubMed Scopus Google Scholar, T. J. N. Plant 2005; PubMed Scopus Google Scholar). In one study the of tomato of PA and T. A. A. G. T. Munnik T. Plant PubMed Scopus Google Scholar). PA occurs as an response in the The of tomato resistance to the C. the Munnik T. Plant J. 2004; PubMed Scopus Google Scholar). The PA is to upstream of the oxidative burst PLC inhibitors the oxidative burst and PA a oxidative burst Munnik T. Plant J. 2004; PubMed Scopus Google Scholar). In the kinase pathway. the of PLD signaling in response to Arabidopsis found to in response to infection M. T. M. PubMed Scopus Google and in PLD expression and PLD protein to the at the site of infection by M. T. M. PubMed Scopus Google Scholar). In a of tomato PLD expression and enzyme activity in response to the fungal elicitor xylanase T. A. A. G. T. Munnik T. Plant PubMed Scopus Google Scholar, L. J. M. A. Munnik T. Plant J. PubMed Scopus Google not or that different pathways the of T. A. A. G. T. Munnik T. Plant PubMed Scopus Google Scholar). the signaling and to the between lipid signals and ROS we a for interacting protein of OXI1. we the of a Ser/Thr kinase that acts downstream of PDK1 and OXI1. It is activated in response to PA and xylanase in a is activated by flagellin and H2O2 in an PDK1-independent evidence that OXI1 and PTI1-2 of and ROS stress signals and PDK1 in a plant pathogen defense and generated as previously (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar). of and by an Arabidopsis cell and The and generated by and by of the the site of the to the The Pti the to and the The of the by The kinase a site in the kinase activation in the role of in the with OXI1, we an to and the in PTI1-2 and generated in the a the in to the The of used as for for and the was generated as a and the The in the of the and the of by generated by The was the plant expression R. J. Res. PubMed Scopus Google Scholar). The OXI1, and the as previously (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar, 5Zegzouti H. Anthony R.G. Jahchan N. Bogre L. Christensen S.K. Proc. Natl. Acad. Sci. U. S. A. 2006; 103: 6404-6409Crossref PubMed Scopus (95) Google Scholar). and the to and The OXI1 was generated by OXI1 the M. Trends Plant Sci. 2005; 10: Full Text Full Text PDF PubMed Scopus Google Scholar). in the was used to an Arabidopsis K. K. R. L. J. L. S. M. G.P. J. Koncz C. PubMed Scopus Google with previously Anthony R.G. S. Plant PubMed Scopus Google Scholar). for activity by on and and of to on with activity was by including and by and the at the and the of the kinase family The used for sequence was was the with the at the in and with of and of the in of and of of The by at for at and of was for at with of The in by two in The in of and and to The by with an and a The was with an of by OXI1 in and OXI1 Arabidopsis a in which the of activity with the stress of was in a kinase in the or of OXI1. and OXI1 in of kinase and of and for at The by of The by and by protein kinases Arabidopsis and for as previously (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar). by for in of and the protein kinases as T. W. J. A. Hirt H. Plant J. PubMed Google Scholar). The used as OXI1, PDK1, and to the kinase at a of The The kinase was for at of the was to and in acid The to of and the activity was a by for in of protein as A. A. C. H. Hirt H. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). of protein the was in the of of protein The was with of protein and of at The with and with kinase The in of kinase and The kinase with of and of and for at of was by protein of protein by to and with either or The was with an and in the phosphatidic acid in xylanase flagellin as previously T.S. Peck S.C. Hirt H. T. J. Biol. Full Text Full Text PDF PubMed Scopus Google or a isolated Arabidopsis and transiently by A. A. C. H. Hirt H. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). activity in was an in to the for at The was by addition of of cell to of was used to of the of and was to the of was a activity was for the and to for the as an an Arabidopsis for we the Arabidopsis Arabidopsis K. K. R. L. J. L. S. M. G.P. J. Koncz C. PubMed Scopus Google was OXI1 as on and on these for activity a S. M. PubMed Scopus Google Scholar). that and for interacting at the and with the OXI1 interacting which very closely Ser/Thr protein of the that the kinases (PTI1-2), and sequence to the tomato kinase a in the activation which in tomato is by the upstream kinase of the sequence to tomato we the as PTI1-2 and The not with PDK1, an upstream of OXI1 We the of a of OXI1, which the to to It has been that binding the domain is a required in the to of PDK1 and is required for activation of OXI1 by PDK1 (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar). The to with OXI1 that the domain is not required for between OXI1 and the we The Pti to GST, and the OXI1 kinase was with and in Arabidopsis We the of these to with in these that OXI1 with the and not with The PDK1-OXI1 was used as a (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar). of the identified kinases that closely to and kinases a activation domain OXI1 and we OXI1 directly the kinases in kinases with or the OXI1 in a protein kinase and not of activity and in the of OXI1. the kinases in the of OXI1, and PTI1-2 an in and was in the of OXI1 We the of OXI1 to of OXI1 was to of the OXI1 not of the protein at the site of OXI1 of the activity and PDK1 and OXI1 by activity of PDK1 is by binding PA and to the domain (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar). of different stresses a PA these and oxidative and pathogen stress (7Testerink C. Munnik T. Trends Plant Sci. 2005; 10: 368-375Abstract Full Text Full Text PDF PubMed Scopus (462) Google Scholar). the activity of PDK1 and OXI1 with stress factors, we in kinase to by the kinases (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar). PDK1 we used the sequence the site to the PDK1 site on the activation of the protein kinase A. Deak M. D.R. EMBO J. PubMed Scopus Google Scholar). OXI1 we used the (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar). shown in PA and xylanase in a in PDK1 activity. The activity PA was the basal activity in by xylanase was at and The elicitor flagellin and H2O2 not the activity of PDK1 as shown in We the effects of stress and the elicitor these not in activity not PA and H2O2 in a significant in activity of OXI1, and xylanase produced a in activity PDK1 in this activity of ABA, and the not activity not of PDK1 on the PLD enzyme activity of PLD by the specific which to as an a with the that PA is T. T. A. Plant PubMed Scopus Google Scholar). and T. T. A. Plant PubMed Scopus Google Scholar). PLC activity the PLC and its Munnik T. Plant J. 2004; PubMed Scopus Google Scholar). the in PDK1 activity by xylanase was of was with the xylanase of and xylanase not in an in PDK1 activity basal whereas the with xylanase in activity to xylanase We the effects of the PLC and found that the the activity of PDK1 with xylanase that the PLC PLC activity in the of we PLC activity isolated C. M. PubMed Scopus Google Scholar). a of the PLC activity by to on The in activity of PDK1 of to the a of of the of the these that PDK1 activity xylanase the PLD and is of PA via the PLC pathway. The of PLD that activated by xylanase in Arabidopsis is PTI1-2 in to we the addition of stress to Arabidopsis the activity of the We different including and to by we to activity not We the of the to the in response to either PA or for PTI1-2 in response to PA, an as as at and to basal PTI1-2 was to the other lipid that has been shown to PDK1 (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google not the we the effects of PA, and H2O2 on kinases PA and xylanase the activity of and H2O2 the activity to a The and kinases not with of the stress We to H2O2 and flagellin signaling to PTI1-2 is on either PLD or PLC the phospholipase of PTI1-2 in response to H2O2 and flagellin was found to the same for the and that the pathways of the phospholipase PDK1 and OXI1 of the PDK1 or OXI1 the activation of the activity of PTI1-2 was in in which the expression of either PDK1 or OXI1 was The was the as previously (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar). The of was with the of a PDK1 The expression of the of the PDK1 The the expression of to a as reported previously (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google Scholar). The expression of OXI1 was an The expression in the same way as for PDK1 by of The of PA, and H2O2 on PTI1-2 activity was in and OXI1 The show that of PDK1 expression the activity of PTI1-2 in response to PA and xylanase to basal PDK1 not the activity of PTI1-2 with H2O2 or flagellin and and In OXI1 expression was PTI1-2 activity was to basal for and and that the signaling pathways for flagellin and H2O2 converge on to PTI1-2 in Arabidopsis of the to oxidative stress and pathogen is the activation of and Arabidopsis plants respond to oxidative stress with an in of including glutathione superoxide and as as the activation of and Y. G. J. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). We used Arabidopsis W. G. Plant J. 10: PubMed Scopus Google T. Y. Genet. PubMed Scopus Google and M. L. Plant 9: PubMed Scopus Google which to the and which activated by oxidative and of these has been in Arabidopsis Y. G. J. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The and for responses to PTI1-2 either or in the of OXI1. We found that PTI1-2 for the effects of H2O2 with the a the The activity in the of PTI1-2 and OXI1. the not the and the to activity. PTI1-2 partially activated the a with OXI1. was the addition of The was not activated either by PTI1-2 or The is in the the not shown and Y. G. J. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The H2O2 significant effects on the response which as an or on the activity by in a have shown that OXI1 expression is required for activation of and M.C. Lecourieux D. Ouaked F. Usher S.L. Petersen L. Okamoto H. Knight H. Peck S.C. Grierson C.S. Hirt H. Knight M.R. Nature. 2004; 427: 858-861Crossref PubMed Scopus (463) Google Scholar). have been shown to activated by PA, and many implicated in plant pathogen for T. G. J. M.R. L. T. J. Nature. PubMed Scopus Google Scholar, Plant 2004; PubMed Scopus Google Scholar). We kinase activity to the of PDK1 activity is by that was activated by xylanase and T.S. Peck S.C. Hirt H. T. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). the activity of activation of closely with the activation of PDK1 the expression of PDK1 was RNAi, xylanase activation of was shown to whereas flagellin activation of was PDK1-independent that activated by a fungal elicitor and a elicitor via different signaling we to a response for in this not has been understanding the functions of oxidative stress and PA signals in is the cross-talk between these different of It is now clear that of PA is by of that the and species of of signaling PA is the PDK1-OXI1 which is implicated in oxidative stress PDK1 is activated by PA, is the upstream signals that PA in PA and ROS signaling in this or the for OXI1. downstream of PA signaling in plants and to the role of PDK1-OXI1 signaling in ROS we a OXI1 as We identified Ser/Thr kinases that homology to the tomato Pti with the Ser/Thr kinase which in resistance to tomato that the in tomato J. Martin G.B. Full Text PDF PubMed Scopus Google Scholar, G.B. J. A. R. T. PubMed Scopus Google Scholar). The kinase a signaling to the oxidative burst in The role of the is one has that in is to the hypersensitive response to tomato J. Martin G.B. Full Text PDF PubMed Scopus Google Scholar). In Arabidopsis PTI1-2 to a family of closely kinases a in the kinase domain with a In tomato this is by OXI1 was to and PTI1-2 in we to significant of in the We the that OXI1 is to and in the show that PTI1-2 has a basal of which not these the of activation of PTI1-2 by OXI1 closely resembles the of OXI1 by PDK1, in which is not required (3Anthony R.G. Henriques R. Helfer A. Meszaros T. Rios G. Testerink C. Munnik T. Deak M. Koncz C. Bogre L. EMBO J. 2004; 23: 572-581Crossref PubMed Scopus (227) Google as to other AGC kinases such as by PDK1 in which is a required in activation H. Anthony R.G. Jahchan N. Bogre L. Christensen S.K. Proc. Natl. Acad. Sci. U. S. A. 2006; 103: 6404-6409Crossref PubMed Scopus (95) Google Scholar). required to OXI1 other family either represent or of different signaling upstream signals that the signaling we different stress factors, including ABA, ROS, and fungal or for to either PDK1 or OXI1. the tested, PA and xylanase activated PDK1, whereas PA, and H2O2 activated OXI1. We not activation of OXI1 by flagellin in this We our on xylanase activation of The downstream of action of fungal is the of PLD in plants L. J. M. A. Munnik T. Plant J. PubMed Scopus Google Scholar). not the activity of PLD and T. A. A. G. T. Munnik T. Plant PubMed Scopus Google that xylanase activated PLD, whereas the and generated PA via a PLC xylanase generated We the of xylanase to PDK1 in the of PLD the specific that PDK1 activated by xylanase in the of PLD and not is with our that this signaling signals in response to the fungal elicitor xylanase not fungal or the tested, such as which not We that xylanase in the activation of a specific PLD localized at the The in PA at the in localized activation of PDK1 in the plants response to is The of the in with of the the cell to the cell is in responses to in the of an to pathogen PLD has as a in J.D. S. S. J. Plant PubMed Scopus Google Scholar, J. Munnik T. Plant PubMed Scopus Google Scholar). In a PLD and is to represent the protein J. Munnik T. Plant PubMed Scopus Google Scholar). The that PLD activation to PA, which functions as a to protein kinases, such as PDK1, and (7Testerink C. Munnik T. Trends Plant Sci. 2005; 10: 368-375Abstract Full Text Full Text PDF PubMed Scopus (462) Google Scholar, C. Munnik T. Plant J. 2004; PubMed Scopus Google Scholar). of PLD activation and PA is the activation of PDK1 and the of to and in a with the plant PDK1 as to the by which In addition to the to Arabidopsis and its PA have been shown to the oxidative burst in Arabidopsis and Y. D. X. Plant PubMed Scopus Google Scholar). It occurs of elicitor and is by inhibitors and Y. D. X. Plant PubMed Scopus Google Scholar). It is to the ROS involved in the plant cell and in The of ROS in plants is to to that in a is by of different to the In this is regulated by a protein kinase R. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). In to of ROS by the to downstream of In Arabidopsis is activated by H2O2, and the resulting PA to a in programmed cell death W. C. C. T. G. Welti R. X. Plant PubMed Scopus Google Scholar). In that the plants cell of PDK1 and OXI1, the PTI1-2 protein is activated in response to PA, and RNA interference that PTI1-2 activation by PA, xylanase PA, and H2O2 OXI1 expression PA signaling to PTI1-2 PDK1 signaling PA has the to such as PDK1 and represent an upstream point of to activation of diverse stress signaling modules. In this activated PDK1 OXI1, which is regulated by ROS such as H2O2 and PTI1-2 in with OXI1 is to PA and ROS signals pathways We have shown that kinase PTI1-2 is to the expression of ROS that PTI1-2 functions in specific ROS signaling It is that PTI1-2 specific pathogen of the PTI1-2 on the downstream by is the of role for the of in the of pathogen defense is now H. A. Hirt H. Trends Plant Sci. 2005; 10: Full Text Full Text PDF PubMed Scopus Google Scholar). have shown in the activation of the and oxidative suggesting that OXI1 functions downstream of ROS upstream of the M.C. Lecourieux D. Ouaked F. Usher S.L. Petersen L. Okamoto H. Knight H. Peck S.C. Grierson C.S. Hirt H. Knight M.R. Nature. 2004; 427: 858-861Crossref PubMed Scopus (463) Google Scholar). In Arabidopsis, and activated by and fungal and ROS T.S. Peck S.C. Hirt H. T. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar, Y. G. J. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, R. A. J. PubMed Scopus Google Scholar). the of PDK1 in we the expression of PDK1 and found that activation of by xylanase was It is that signaling downstream of OXI1 and resulting in the activation of in response to different play a role upstream and have been implicated in the activation of the H. N. K. S. K. Jones J.D. N. Plant PubMed Scopus Google Scholar). The in this study evidence that PDK1 is involved in response is of the ROS signaling that OXI1 and its interacting partner required to the and PLD enzyme activity to and the downstream of such as We very to for the and We for the Munnik for the PLC and Peck for and and for the with