ESCRT-dependent components in fungal phytopathogens
At the molecular level, components of the ESCRT pathways are well understood in only a few model phytopathogenic fungi, including F. graminearum , M. oryzae and Ustilago maydis (Table 1). Of these, the two ascomycetes (F. graminearum and M. oryzae ) are respectively responsible for Fusarium head blight of barley/wheat and rice blast disease (Xie et al., 2019a; Sun et al., 2022). The basidiomycetous species U. maydis is the causal agent of smut on maize and teosinte, a wild grass species considered the ancestor of modern maize (Bölker et al., 1992; Pérez-Rodríguez et al., 2021). Overall, these studies showed that the basic assembly and sequential recruitment of ESCRT components is likely consistent with that of the yeast. This is consistent with the fact that the ESCRT pathway is conserved with only some components apparently non-essential in certain lineages (Leung et al., 2008). Also, some ESCRT components are critical for growth, stress response reproduction system, while others affect pathogenesis.
Several gene knockout studies have been performed to determine the impact of ESCRT-associated genes in these pathogens. A recent study by Xie et al., (2016) was the first to report on ESCRT-0 subunit Vps27 functions in F. graminearum . The authors revealed that Vps27 is crucial for the pathogen’s development, conidiation and virulence. They also showed that ESCRT proteins -I, -II and -III are essential for endocytic delivery into the vacuole, therefore aiding in the production of mycotoxins (Xie et al., (2019b)). In U. maydis , the removal of ESCRT-III Did2 caused defects on hyphal growth as well as impaired conveyance of early and late endosomes (MVBs) (Haag et al., 2017). InM. oryzae , de-ubiquitination enzyme Doa4 is essential for ensuring pathogenicity and infection-related morphogenesis (Wang et al., 2018; Que et al., 2020).
The above studies on phytopathogenic fungi are consistent with those conducted on human pathogenic fungi. For example, in C. neoformans, Doa4 mutants exhibited reduced pathogenicity and phenotypic defects (Amerik et al., 2000a; Fang et al., 2012; Que et al., 2020). InC. albicans , deletion mutants of ESCRT-III SnF7 are associated with acute impairment on hyphal germination (Yang et al., 2020). Additionally, DUBs such as Ubp14, Ubp8 and Ubp4 have been shown to play critical roles in conidiation, growth and, most importantly, pathogenicity (Wang et al., 2018; Que et al., 2020 and Yang et al., 2020).