Challenges and progress towards understanding the role of effectors in plant–fungal interactions

Both mutualistic and biotrophic pathogenic fungi rely on living host plants for growth and reproduction and must modify host cell structure and function for successful infection. The deployment of a diverse set of secreted virulence determinants referred to as ‘effectors’, many of which are directly delivered into the host cell, is postulated to be the key to host infection. This review provides a snapshot of the current progress in fungal effector biology. Recent genome sequencing of rust and powdery mildew obligate biotrophs has provided insight into the repertoires of potential effectors of these highly specialised pathogens. Identification of the first host-translocated effectors from mutualistic fungi has revealed that these fungi also manipulate host cells through effectors. The biological activities of some fungal effectors are just beginning to be revealed, while much uncertainty still surrounds the mechanisms of transport into host cells.