MAP2K3 and infection: MKK3 was first reported to play a role during plant–pathogen interaction (Dóczi et al., 2007) (Figure 1A): mkk3 knock-out mutants were shown to be hypersensitive to infection by Pseudomonas syringae DC3000 whereas Arabidopsis lines expressing a constitutively active MKK3 (MKK3EE) showed mild resistance to the pathogen.