Roles of iron in plant defence and fungal virulence.

Iron is an essential component of various proteins and pigments for both plants and pathogenic fungi. However, redox cycling between the ferric and ferrous forms of iron can also catalyse the production of dangerous free radicals and iron homeostasis is therefore tightly regulated. Our work has indicated that monocot plants challenged by pathogenic fungi redistribute cellular iron to the apoplast in a controlled manner to activate both intracellular and extracellular defences. In the apoplast, the accumulation of free, reactive ferric iron mediates defensive H2O2 production. Inside the cell, this efflux of iron creates a state of iron depletion, which directs the transcription of pathogenesis-related genes in concert with H2O2. In this addendum, we describe differences between the roles of iron in mediation of the oxidative burst in cereal and Arabidopsis responses to fungal pathogens. Also, we discuss the implications of current work concerning fungal iron uptake on host defence strategies.