Authors: Andrea Daxberger Andrea Nemak Axel Mithöfer Judith Fliegmann Wilco Ligterink Heribert Hirt Jürgen Ebel
Publish Date: 2006/11/23
Volume: 225, Issue: 6, Pages: 1559-1571
Abstract
Plants recognize microbial pathogens by discriminating pathogenassociated molecular patterns from selfstructures We study the nonhost disease resistance of soybean Glycine max L to the oomycete Phytophthora sojae Soybean senses a specific molecular pattern consisting of a branched heptaglucoside that is present in the oomycetal cell walls Recognition of this elicitor may be achieved through a βglucanbinding protein which forms part of a proposed receptor complex Subsequently soybean mounts a complex defense response which includes the increase of the cytosolic calcium concentration the production of reactive oxygen species and the activation of genes responsible for the synthesis of phytoalexins We now report the identification of two mitogenactivated protein kinases MAPKs and one MAPK kinase MAPKK that may function as signaling elements in triggering the resistance response The use of specific antisera enabled the identification of GmMPKs 3 and 6 whose activity is enhanced within the signaling pathway leading to defense reactions Elicitor specificity of MAPK activation as well as the sensitivity against inhibitors suggested these kinases as part of the βglucan signal transduction pathway An upstream GmMKK1 was identified based on sequence similarity to other plant MAPKKs and its interaction with the MAPKs was analyzed Recombinant GmMKK1 interacted predominantly with GmMPK6 with concomitant phosphorylation of the MAPK protein Moreover a preferential physical interaction between GmMKK1 and GmMPK6 was demonstrated in yeast These results suggest a role of a MAPK cascade in mediating βglucan signal transduction in soybean similar to other triggers that activate MAPKs during innate immune responses in plants
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