Effector biology during biotrophic invasion of plant cells

Abstract

Several obligate biotrophic phytopathogens, namely oomycetes and fungi, invade and feed on living plant cells through specialized structures known as haustoria. Deploying an arsenal of secreted proteins called effectors, these pathogens balance their parasitic propagation by subverting plant immunity without sacrificing host cells. Such secreted proteins, which are thought to be delivered by haustoria, conceivably reprogram host cells and instigate structural modifications, in addition to the modulation of various cellular processes. As effectors represent tools to assist disease resistance breeding, this short review provides a bird’s eye view on the relationship between the virulence function of effectors and their subcellular localization in host cells.

Effectors involved in fungal–fungal interaction lead to a rare phenomenon of hyperbiotrophy in the tritrophic system biocontrol agent–powdery mildew–plant

“…To establish infection, they depend on living cells where they form a specialized feeding structure, the haustorium, which invaginates the plasma membrane of the host epidermal cell. The interaction between the haustorium and the plant cell is tightly regulated so that the fungus can obtain resources from the plant without killing it (Chaudhari et al ., ). Diversion of nutrients from the host to powdery mildew fungus leads to the production of mycelium, conidiophores and conidia, thus maintaining the development and asexual reproduction of the fungus.…”

“…Moreover, the B. graminis genome was the first to be released among powdery mildew species (Spanu et al ., ), which led to the annotation of 6469 genes from which 491 were identified as candidate secreted effector proteins (CSEPs) (Pedersen et al ., ). As in many plant–pathogen interactions, effector proteins are involved in disease development by, among other functions, suppressing host defense responses and affecting the host metabolism for the purpose of nutrient acquisition by the pathogen (Chaudhari et al ., ). In spite of the overwhelming evidence linking CSEPs to the virulence arsenal of plant pathogens, very little is known about their functionality (Sonah et al ., ).…”

Infection assays in Arabidopsis reveal candidate effectors from the poplar rust fungus that promote susceptibility to bacteria and oomycete pathogens

“…The suppression and evasion of innate immunity are undoubtedly important aspects of obligate biotrophy; they are, however, only a starting point in the establishment of a successful infection. Indeed, it has emerged recently that effectors also target cellular structures and processes that are not directly related to the plant immune system, thus suggesting that pathogens not only suppress immune responses, but also achieve a deep manipulation of their hosts (reviewed in Chaudhari et al, 2014;Giraldo and Valent, 2013;Win et al, 2012).…”

Identification of eight effector candidate genes involved in early aggressiveness of the barley powdery mildew fungus

“…Recent progress was made with the release of the Bgh genome sequence and identification of 491 genes encoding candidates for secreted effector proteins (CSEPs) (Spanu et al, 2010;Pedersen et al, 2012). Such effector proteins are thought to facilitate disease development, for instance by suppressing host defences and by affecting the host cell metabolism to favour nutrient acquisition (Chaudhari et al, 2014).…”