The septin protein Sep4 facilitates host infection by plant fungal pathogens via mediating initiation of infection structure formation

Abstract

Many phytopathogenic fungi use infection structures (IFSs, i.e., appressoria and infection cushions) to penetrate host cuticles. However, the conserved mechanisms that mediate initiation of IFS formation in divergent pathogens upon sensing the presence of host plants remain obscure. Here, we demonstrate that a conserved septin gene SEP4 plays crucial roles in this process. Disruption of SEP4 in the plant grey mould fungus Botrytis cinerea completely blocked IFS formation and abolished the virulence of ΔBcsep4 mutants on unwounded hosts. During IFS formation, mutants lacking SEP4 could produce reactive oxygen species (ROS) normally. Inhibition of ROS production in strains harbouring the SEP4 gene resulted in disordered assembly of Sep4 and the subsequent failure to form infection cushions, suggesting that proper Sep4 assembly regulated by ROS is required for initiation of IFS formation and infection. Moreover, loss of SEP4 severely impaired mutant conidiation, melanin and chitin accumulation in hyphal tips and lesion expansion on wounded hosts, but significantly promoted germ tube elongation and sclerotium production. SEP4-mediated fungal pathogenic development, including IFS formation, was validated in the hemibiotroph Magnaporthe oryzae. Our findings indicate that Sep4 plays pleiotropic roles in B. cinerea development and specifically facilities host infection by mediating initiation of IFS formation in divergent plant fungal pathogens in response to ROS signaling.

The pre‐rRNA processing factor Nop53 regulates fungal development and pathogenesis via mediating production of reactive oxygen species

“…S9). Consistent with our previous findings (Feng et al ., ), inhibition of ROS production by exogenous DPI, a flavoprotein inhibitor that blocks ROS production by NADPH oxidases (Nox) (Chandel et al ., ), greatly reduced ROS production in hyphal ends or mycelia forming infection structures (Supporting Information Fig. S9).…”

“…5F and G). Trypan blue staining analysis (Feng et al, 2017) demonstrated that the mutant conidia could germinate normally on the host leaf surfaces. However, they failed to penetrate into host tissue (Supporting Information Fig.…”

“…Plant pathogens may encounter diverse stresses during interaction with hosts. To investigate how BcNOP53 affects pathogenesis-associated stress adaptation, we first cultured the WT, DBcnop53, and C-DBcnop53 strains on CM containing the oxidative stress agent H 2 O 2 , osmotic stress agents NaCl, KCl, sorbitol or glucose, as well as cell walldamaging agent Congo red or sodium dodecyl sulfate (SDS) (Heller et al, 2012;Feng et al, 2017). We then evaluated mycelial development of these strains.…”

“…To investigate the roles of NOP53 in B. cinerea pathogenic development, we determined the effect of BcNOP53 on the formation of appressoria and infection cushions that are required for host penetration and virulence (Gourgues et al, 2004;Feng et al, 2017). Appressorium formation of B. cinerea requires a hard surface and can be induced on glass slides/coverslips (Feng et al, 2017). We inoculated B. cinerea strains B05.10, DBcnop53, and C-DBcnop53 on inductive (glass slide/coverslip, cellophane membrane) surfaces (Feng et al, 2017).…”

The key gluconeogenic gene PCK1 is crucial for virulence of Botrytis cinerea via initiating its conidial germination and host penetration

“…The sensitivities of the tested strains to different stresses were analyzed as previously described (Feng et al ., ). Briefly, conidial suspension (1 μl, 1 × 10 6 conidia ml −1 ) or mycelial plugs (5 mm in diameter) of the B. cinerea WT, Δ Bcpck1 mutant and complemented strains were inoculated onto CM supplemented with different concentrations of stress agents, including osmotic stress agents NaCl and KCl, oxidative stress reagent H 2 O 2 and cell wall disturbing agents SDS and Congo Red.…”