The role of effectors of biotrophic and hemibiotrophic fungi in infection

Abstract

Biotrophic and hemibiotrophic fungi are successful groups of plant pathogens that require living plant tissue to survive and complete their life cycle. Members of these groups include the rust fungi and powdery mildews and species in the Ustilago, Cladosporium and Magnaporthe genera. Collectively, they represent some of the most destructive plant parasites, causing huge economic losses and threatening global food security. During plant infection, pathogens synthesize and secrete effector proteins, some of which are translocated into the plant cytosol where they can alter the host's response to the invading pathogen. In a successful infection, pathogen effectors facilitate suppression of the plant's immune system and orchestrate the reprogramming of the infected tissue so that it becomes a source of nutrients that are required by the pathogen to support its growth and development. This review summarizes our current understanding of the function of fungal effectors in infection.

Figure 1

Schematic diagram of fungal infection structures in and around an infected leaf cell. Four different fungal pathogens have different infection strategies, either invading the intercellular space (Cladosporium fulvum, C.f.), propagating hyphae within cells (Magnaporthe oryzae, M.o.), or penetrating host cells via haustoria (Blumeria graminis, B.g. and Melampsora lini, M.l.) (see text for details). Effectors of the different pathogens (colored shapes) are secreted from the fungal structures and either act in the apoplast or are delivered into the host cell. A, appressorium; BIC, biotrophic invasive complex; E, effector; EHM, extrahaustorial membrane; EHMX, extrahaustorial matrix; EIHM, extrainvasive hyphal membrane; FCW, fungal cell wall; FPM, fungal plasma membrane; H, haustorium; IH, invasive hyphae; N, neckband; PCW, plant cell wall; PPM, plant plasma membrane.