The Arabidopsis Mitogen-Activated Protein Kinase Kinase MKK3 Is Upstream of Group C Mitogen-Activated Protein Kinases and Participates in Pathogen Signaling

Abstract

Although the Arabidopsis thaliana genome contains genes encoding 20 mitogen-activated protein kinases (MAPKs) and 10 MAPK kinases (MAPKKs), most of them are still functionally uncharacterized. In this work, we analyzed the function of the group B MAPK kinase, MKK3. Transgenic ProMKK3:GUS lines showed basal expression in vascular tissues that was strongly induced by Pseudomonas syringae pv tomato strain DC3000 (Pst DC3000) infection but not by abiotic stresses. The growth of virulent Pst DC3000 was increased in mkk3 knockout plants and decreased in MKK3-overexpressing plants. Moreover, MKK3 overexpression lines showed increased expression of several PR genes. By yeast two-hybrid analysis, coimmunoprecipitation, and protein kinase assays, MKK3 was revealed to be an upstream activator of the group C MAPKs MPK1, MPK2, MPK7, and MPK14. Flagellin-derived flg22 peptide strongly activated MPK6 but resulted in poor activation of MPK7. By contrast, MPK6 and MPK7 were both activated by H 2 O 2 , but only MPK7 activation was enhanced by MKK3. In agreement with the notion that MKK3 regulates the expression of PR genes, ProPR1:GUS expression was strongly enhanced by coexpression of MKK3-MPK7. Our results reveal that the MKK3 pathway plays a role in pathogen defense and further underscore the importance and complexity of MAPK signaling in plant stress responses.

A MAP Kinase Kinase Interacts with SymRK and Regulates Nodule Organogenesis in Lotus japonicus

“…Several plant MAPKKs have been shown to play important roles in the cellular responses to different biotic and abiotic cues (Kiegerl et al, 2000;Mody et al, 2003;Dó czi et al, 2007;Takahashi et al, 2007). SIMKK, an alfalfa MAPKK, exhibiting 88% similarity with Lotus SIP2 at the amino acid level, has been implicated in the salt-induced activation of SIMK during the response to fungal elicitor (Kiegerl et al, 2000;Cardinale et al, 2002).…”

“…The Arabidopsis MKK1/ MKK2-MPK4/MPK6 cascades have previously been shown to play important roles in the responses to salt and cold stresses and pathogen attack (Teige et al, 2004;Meszá ros et al, 2006;Gao et al, 2008;Qiu et al, 2008b). Arabidopsis MKK3 participates in signaling cascades elicited by pathogen infection (Dó czi et al, 2007;Takahashi et al, 2007). The Arabidopsis MKK4/MKK5-MPK3/MPK6 cascades play important roles in the regulation of plant development and biotic stress (Asai et al, 2002;Wang et al, 2007).…”

MAP KINASE PHOSPHATASE1 and PROTEIN TYROSINE PHOSPHATASE1 Are Repressors of Salicylic Acid Synthesis and SNC1-Mediated Responses inArabidopsis

“…The open reading frames of MPK6 and MKP1 were cloned into the plant expression vector pGREEN and constitutively active MKK4 EE (with both putative phosphorylation sites changed to Glu residues: T224E and S230E) into pRT100 and fused at their C-terminal end either to a triple HA epitope (MPK6 and MKK4 EE ) or to a c-myc epitope (MKP1), as described before (Doczi et al, 2007). Arabidopsis protoplast transient expression assays and protein extraction were performed as described (Ouaked et al, 2003).…”

Activation of AtMPK9 through autophosphorylation that makes it independent of the canonical MAPK cascades

“…The myc-tagged, constitutively active, gain of function (GOF) mutant form of AtMKK4 was inserted into pEU3-NII-Gateway destination vector by Gateway cloning. PCR fragments of AtMPK9 mutants were cloned into pRT-HA vector [17] using NotI and NcoI restriction endonucleases (Fermentas) for protoplast transformation. The myc-tagged, GOF-MKK constructs were recloned into pK2GW7 vector [18] by Gateway conversion.…”