Infection Structure-Specific Reductive Iron Assimilation Is Required for Cell Wall Integrity and Full Virulence of the Maize Pathogen Colletotrichum graminicola

Abstract

Ferroxidases are essential components of the high-affinity reductive iron assimilation pathway in fungi. Two ferroxidase genes, FET3-1 and FET3-2, have been identified in the genome of the maize anthracnose fungus Colletotrichum graminicola. Complementation of growth defects of the ferroxidase-deficient Saccharomyces cerevisiae strain Δfet3fet4 showed that both Fet3-1 and Fet3-2 of C. graminicola represent functional ferroxidases. Expression of enhanced green fluorescent protein fusions in yeast and C. graminicola indicated that both ferroxidase proteins localize to the plasma membrane. Transcript abundance of FET3-1 increased dramatically under iron-limiting conditions but those of FET3-2 were hardly detectable. Δfet3-1 and Δfet3-2 single as well as Δfet3-1/2 double-deletion strains were generated. Under iron-sufficient or deficient conditions, vegetative growth rates of these strains did not significantly differ from that of the wild type but Δfet3-1 and Δfet3-1/2 strains showed increased sensitivity to reactive oxygen species. Furthermore, under iron-limiting conditions, appressoria of Δfet3-1 and Δfet3-1/2 strains showed significantly reduced transcript abundance of a class V chitin synthase and exhibited severe cell wall defects. Infection assays on intact and wounded maize leaves, quantitative data of infection structure differentiation, and infection stage-specific expression of FET3-1 showed that reductive iron assimilation is required for appressorial penetration, biotrophic development, and full virulence.

Green leaf volatiles and jasmonic acid enhance susceptibility to anthracnose diseases caused by Colletotrichum graminicola in maize

“…The relatively high amounts of SA present in both lox10‐3 and opr7‐5 opr8‐2 mutants before or soon after infection (1 dpi) directly coincide with appressoria formation and initiation of biotrophic growth by C. graminicola (Vargas et al , ). Reactive oxygen species are rapidly produced by plants on infection via SA signalling and are involved in fungal defence and growth inhibition, including C. graminicola (Apostol et al ., ; Mellersh et al , ; Albarouki and Deising, ). It is possible that the quick induction of SA‐related defences inhibits catalase‐mediated degradation of H 2 O 2 , allowing build‐up of H 2 O 2 around points of appressorial penetration, which stops penetration and/or growth of C. graminicola .…”

Ferric ions accumulate in the walls of metabolically inactivating Saccharomyces cerevisiae cells and are reductively mobilized during reactivation

“…We suspect that the CW Fe accumulation phenomenon discovered here is a general property of fungi, and that it promotes their survival. If so, inhibiting CW Fe may diminish the ability of pathogenic fungi to survive in a host (7). Deleting the Fet3 ferroxidases on the plasma membrane of pathogenic fungus Colletotrichum graminicola caused an 80% decline in chitin synthase and defects in the CW that reduced virulence.…”

“…The CW allows cells to adhere to each other and to solid supports, and is involved in mating and morphogenesis (3). It affects the virulence of pathogenic fungi and thus has biomedical importance (7-11). …”

Intracellular siderophore but not extracellular siderophore is required for full virulence in Metarhizium robertsii

“…Infection of mouse macrophages with A. fumigatus wild type, but not with a ΔsidA strain which produces neither extracellular nor intracellular siderophores, induced the expression of TNFα, a cytokine essential for host defense (Roilides et al, 1998;Seifert et al, 2008). Siderophore-mediated pathogen recognition also occurs in plants as Colletotrichum graminicola, the causal agent of anthracnose stalk rot and leaf blight of maize, shuts down SIA during biotrophic growth to avoid detection and redeploys SIA during necrotrophic growth (Albarouki and Deising, 2013;Albarouki et al, 2014). Metachelin A is unique among fungi because it is O-mannosylated, a modification closely resembling the C-glycosylation of salmochelin which is deployed by some animal-pathogenic bacteria to evade siderocalin sequestration (Abergel et al, 2006;Muller et al, 2009).…”

“…In the plant pathogens Cochliobolus heterostrophus, Gibberella zeae and Alternaria alternata, SIA and not RIA is essential for full virulence (Chen et al, 2013;Condon et al, 2014;Oide et al, 2006;Park et al, 2006;Schrettl et al, 2004). In Colletotrichum graminicola, SIA and RIA have complementary roles: RIA is deployed during the biotrophic phase, when extracellular siderophore production is downregulated to avoid host detection; SIA is then used to support necrotrophic growth (Albarouki and Deising, 2013;Albarouki et al, 2014). In Ustilago maydis, SIA is dispensable for virulence whereas RIA impairment strongly affects growth and sporulation in planta.…”