How do oomycete effectors interfere with plant life?

► The genomes of oomycete pathogens each encode hundreds of effector proteins. ► Secreted effectors act on plant extracellular enzymes, cell walls and membranes. ► Host-translocated effectors of the RXLR and CRN class act inside the host cell. ► Oomycetes extensively manipulate host defence to successfully establish infection. ► Biotrophic pathogens affect host physiology/metabolism to aid nutrient acquisition. Oomycete genomes have yielded a large number of predicted effector proteins that collectively interfere with plant life in order to create a favourable environment for pathogen infection. Oomycetes secrete effectors that can be active in the host's extracellular environment, for example inhibiting host defence enzymes, or inside host cells where they can interfere with plant processes, in particular suppression of defence. Two classes of effectors are known to be host-translocated: the RXLRs and Crinklers. Many effectors show defence-suppressive activity that is important for pathogen virulence. A striking example is AVR3a of Phytophthora infestans that targets an ubiquitin ligase, the stabilisation of which may prevent host cell death. The quest for other effector targets and mechanisms is in full swing.