Haustorium initiation and early development

Abstract

The haustoria of the Orobanchaceae are formed in response to chemical and physical stimuli provided by host roots. Several quinones and phenols have been identified that induce haustorium development, suggesting that parasites recognise a multiplicity of molecules in the rhizosphere associated with host roots. In some cases the parasite activates host cell wall peroxidases which generate haustorium-inducing factors. The redox states of the molecules are critical for activity. Transitions from oxidised quinones to reduced phenols generate semiquinone intermediates that initiate haustorium differentiation. Signalling is interrupted by inhibiting quinone oxidoreductases in the parasite through gene silencing. This chapter reviews our current state of knowledge about early haustorium development in Orobanchaceae with particular emphasis on how haustorium-inducing molecules are recognised by parasitic plants.