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).