ELEMENTS OF HOST DISEASE RESISTANCE SIGNALLING HIJACKED BY MYCOSHAERELLA GRAMINICOLA DURING SUCCESSFUL WHEAT LEAF INFECTION

Many race- or isolate-specific disease resistance responses of plants towards pathogens (incompatible interactions) invoke hypersensitive response (HR)-like programmed cell death (PCD), and the co-ordinate activation of mitogen-activated protein kinases homologous to Arabidopsis AtMPK6 and AtMPK3 (or Tobacco SIPK and WIPK), respectively. Resistance of wheat leaves towards a major necrotrophic fungal pathogen; Mycosphaerella graminicola can also operate at an isolate-cultivar specific level but occurs in the absence of HR-like PCD. Instead PCD is strongly associated with the compatible interaction and is triggered during disease symptom expression. A strong transcriptional activation of TaMPK3, the wheat homologue of Arabidopsis AtMPK3, is observed immediately preceding PCD and symptom development in the compatible interaction. Generation and use of TaMPK3 and TaMPK6-specific antibodies in western blots and in coupled immunoprecipitation-protein kinase assays demonstrated that the TaMPK3 protein also accumulated, and was subsequently post-translationally activated, during the compatible interaction in parallel to PCD. In contrast, no increase in expression, protein levels or post-translational activation of TaMPK6 was observed at any stage of either compatible or incompatible interactions. However, the protei