Ustilago maydis effectors and their impact on virulence

Abstract

Biotrophic fungal plant pathogens establish an intimate relationship with their host to support the infection process. Central to this strategy is the secretion of a range of protein effectors that enable the pathogen to evade plant immune defences and modulate host metabolism to meet its needs. In this Review, using the smut fungus Ustilago maydis as an example, we discuss new insights into the effector repertoire of smut fungi that have been gained from comparative genomics and discuss the molecular mechanisms by which U. maydis effectors change processes in the plant host. Finally, we examine how the expression of effector genes and effector secretion are coordinated with fungal development in the host.

The core effector Cce1 is required for early infection of maize by Ustilago maydis

“…Furthermore, most effectors lack conserved functional domains as well as orthologs outside the genus (Win et al, ). Many effector proteins are cysteine‐rich and presumably able to form disulfide bonds to stabilize their tertiary structure in the harsh oxidative conditions of the plant apoplast (Lanver et al, ; Win et al, ).…”

“…In many cases, however, deletion of a single effector or even a whole cluster does not affect U. maydis virulence, presumably due to functional redundancy. U. maydis also contains core effectors, which are highly conserved among smut fungi and are likely to play a crucial role in the infection process (Lanver et al, ).…”

Smut infection of perennial hosts: the genome and the transcriptome of the Brassicaceae smut fungus Thecaphora thlaspeos reveal functionally conserved and novel effectors

“…smut (Rabe et al ., ). In addition, functional analysis in U. maydis confirmed the contribution of single effector proteins to fungal virulence (Lanver et al ., ). For example, Pep1, a protein essential for fungal penetration, was initially identified outside of the effector clusters and was characterized as an apoplastic peroxidase inhibitor (Doehlemann et al ., ; Hemetsberger et al ., ), which is conserved in several grass smut species as well as the dicot‐infecting smut Melanopsichium pennsylvanicum (Hemetsberger et al ., ).…”

The Shifting Transcriptional Response of Maize Smut Fungus

“…Initially totally encased by the plant's plasma membrane, the fungus then grows into the mesophyll and nutrient-rich vascular tissue of its host. The infected plant cells divide rapidly and enlarge, forming tumors that are filled with fungal hyphae and, with time, fungal spores (Lanver et al, 2017).…”

“…Many of the 476 effectors secreted by U. maydis lack established structural or functional domains (Schuster et al, 2017), and only 5 of these have been characterized in detail (Lanver et al, 2017). Characterizing the remaining effectors and pinpointing the stages of infection at which they are active would this fungus, and possibly suggest ways to contain it.…”