Activation of a mitogen-activated protein kinase cascade induces WRKY family of transcription factors and defense genes in tobacco.
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.
Kim
Cha Young
CY
Department of Biochemistry, University of Missouri-Columbia, 117 Schweitzer Hall, Columbia, MO 65211, USA.
Zhang
Shuqun
S
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
D018744:DNA, Plant; D010940:Plant Proteins; D014157:Transcription Factors