title: Activation of a mitogen-activated protein kinase cascade induces WRKY family of transcription factors and defense genes in tobacco.
abstract: Mitogen-activated protein kinase (MAPK) cascades are important signaling modules in eukaryotic cells that convert signals generated from the receptors/sensors to cellular responses. Upon activation, MAPKs can be translocated into nuclei where they phosphorylate transcription factors, which in turn activate gene expression. We recently identified NtMEK2, a tobacco MAPK kinase, as the upstream kinase of SIPK and WIPK, two well-characterized tobacco stress-responsive MAPKs. In the conditional gain-of-function NtMEK2DD transgenic tobacco plants, the activation of endogenous SIPK and WIPK by NtMEK2DD induces several groups of defense genes, including 3-hydroxy-3-methlyglutaryl CoA reductase (HMGR), basic pathogenesis related (PR) genes, systemic acquired resistance gene 8.2 (Sar 8.2), and harpin-induced gene1 (Hin1). To identify the transcription factor(s) involved in the activation of these defense genes, we performed gel-mobility shift assays using nuclear extracts from NtMEK2DD plants. Among the common cis-acting elements present in the promoters of defense-related genes, we observed a strong increase in the binding activity to the W box in nuclear extracts from the NtMEK2DD plants but not the control NtMEK2KR plants. The elevated W-box-binding activity in the nuclear extracts cannot be reversed by phosphatase treatment, excluding the possibility of a direct phosphorylation regulation of WRKY transcription factors by SIPK/WIPK. Instead, we observed a rapid increase in the expression of several WRKY genes in the NtMEK2DD plants. These results suggest that the increase in W-box-binding activity after SIPK/WIPK activation is a result of WRKY gene activation, and the NtMEK2-SIPK/WIPK cascade is involved in regulating the expression of genes ranging from transcription factors to defense genes further downstream during plant defense responses.
authors.affiliation: Department of Biochemistry, University of Missouri-Columbia, 117 Schweitzer Hall, Columbia, MO 65211, USA.
authors.forename: Cha Young
authors.initials: CY
authors.lastname: Kim
authors.forename: Shuqun
authors.initials: S
authors.lastname: Zhang
mesh_terms: D001483:Base Sequence; D018744:DNA, Plant / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D020935:MAP Kinase Signaling System; D008954:Models, Biological; D005810:Multigene Family; D010940:Plant Proteins / Q000096:biosynthesis* / Q000235:genetics; D030821:Plants, Genetically Modified; D014026:Nicotiana / Q000235:genetics* / Q000378:metabolism*; D014027:Tobacco Mosaic Virus / Q000472:pathogenicity; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D015533:Transcriptional Activation
chemical_list: D018744:DNA, Plant; D010940:Plant Proteins; D014157:Transcription Factors