title: Arabidopsis MKS1 is involved in basal immunity and requires an intact N-terminal domain for proper function.
abstract: BACKGROUND
  Innate immune signaling pathways in animals and plants are regulated by mitogen-activated protein kinase (MAPK) cascades. MAP kinase 4 (MPK4) functions downstream of innate immune receptors via a nuclear substrate MKS1 to regulate the activity of the WRKY33 transcription factor, which in turn controls the production of anti-microbial phytoalexins.
  
  
  RESULTS
  We investigate the role of MKS1 in basal resistance and the importance of its N- and C-terminal domains for MKS1 function. We used the information that mks1 loss-of-function partially suppresses the mpk4 loss-of-function phenotype, and that transgenic expression of functional MKS1 in mpk4/mks1 double mutants reverted the mpk4 dwarf phenotype. Transformation of mks1/mpk4 with mutant versions of MKS1 constructs showed that a single amino acid substitution in a putative MAP kinase docking domain, MKS1-L32A, or a truncated MKS1 version unable to interact with WRKY33, were deficient in reverting the double mutant to the mpk4 phenotype. These results demonstrate functional requirement in MKS1 for the interaction with MPK4 and WRKY33. In addition, nuclear localization of MKS1 was shown to depend on an intact N-terminal domain. Furthermore, loss-of-function mks1 mutants exhibited increased susceptibility to strains of Pseudomonas syringae and Hyaloperonospora arabidopsidis, indicating that MKS1 plays a role in basal defense responses.
  
  
  CONCLUSIONS
  Taken together, our results indicate that MKS1 function and subcellular location requires an intact N-terminus important for both MPK4 and WRKY33 interactions.
authors.affiliation: Department of Biology, University of Copenhagen, Copenhagen, Denmark. joseph.reiner@nist.gov
authors.forename: Klaus
authors.initials: K
authors.lastname: Petersen
authors.forename: Jin-Long
authors.initials: JL
authors.lastname: Qiu
authors.forename: Juri
authors.initials: J
authors.lastname: Lütje
authors.forename: Berthe Katrine
authors.initials: BK
authors.lastname: Fiil
authors.forename: Sidsel
authors.initials: S
authors.lastname: Hansen
authors.forename: John
authors.initials: J
authors.lastname: Mundy
authors.forename: Morten
authors.initials: M
authors.lastname: Petersen
mesh_terms: D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D005838:Genotype; D007107:Immune System; D020935:MAP Kinase Signaling System; D018613:Microscopy, Confocal / Q000379:methods; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009687:Nuclear Proteins; D010641:Phenotype; D010750:Phosphoproteins / Q000737:chemistry / Q000502:physiology*; D018521:Plant Physiological Phenomena; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; C503586:MKS1 protein, Arabidopsis; D009687:Nuclear Proteins; D010750:Phosphoproteins; D014157:Transcription Factors; C517860:WRKY33 protein, Arabidopsis; C436292:AtMPK4 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases