Fusarium graminearumSte3 G-Protein Coupled Receptor: A Mediator of Hyphal Chemotropism and Pathogenesis

Abstract

Fusarium head blight of wheat, caused by the filamentous fungus Fusarium graminearum , leads to devastating global food shortages and economic losses. Fungal hyphal chemotropism has been shown to be a major contributor to host-pathogen interactions. Here, the role of the opposite mating type GPCR, Ste3, is characterized with respect to F. graminearum chemotropism and pathogenicity. These findings contribute to our understanding of the mechanisms underlying fungal chemotropism and pathogenesis.

Fusarium graminearumSte2 and Ste3 Receptors Undergo Peroxidase Induced Heterodimerization

“…GPCR heterodimerization has been shown to control a wide range of cellular and physiological processes that differ from the functions of the monomeric versions of the receptors (Calebiro & Godbole, 2018; Sleno & Hébert, 2018). In the plant pathogen F. graminearum , we have demonstrated that two GPCRs, Fg Ste2 and Fg Ste3, are involved in mediating chemotropic responses to host derived peroxidases (Sharma et al, 2022a; Sridhar et al, 2020). Individual deletions of each receptor abolished chemotropic response towards peroxidase, highlighting that each receptor was only active in the presence of the other.…”

“…With respect to the relationship between GPCRs and NOX, in F. oxysporum , NOX expression has been shown to regulate chemotropic bending (Nordzieke et al, 2019; Sharma et al, 2022a). Specifically, deletion of NOX genes in F. oxysporum eliminated chemotropism, where addition of exogeneous H 2 O 2 to Δ noxB and Δ noxR knockouts rescued chemotropic growth.…”

“…That no clear concentration-dependence could be established may pertain to our current inability to quantify the HRP-derived ligand, due to the identity of the ligand being unknown at this time. In terms of investigations towards identifying the nature of the ligand, previous investigations from our lab have shown that the ligand being formed is of fungal origin (Sharma et al, 2022a; Sridhar et al, 2020), with the enzyme substrate presented either on the cell wall or cell membrane or both in F. graminearum , which are rich sources of peroxidase substrates (Lüthje & Martinez-Cortes, 2018; Schneider et al, 2023). However that HRP-alone can stimulate the Fg Ste2- Fg Ste3 heterodimer formation in S .…”

“…Δ Fg Ste2 and Δ Fg Ste3 deletion strains each individually lead to complete elimination of the chemotropic response to horse radish peroxidase (HRP). These individual deletions also both led to decreased pathogenicity on germinating wheat coleoptiles, underscoring the relevance of these receptors in mediating infection (Sharma et al, 2022a). Mechanistically, the receptor deletions individually led to decreased CWI-MAPK signaling compared to wildtype (WT) F. graminearum .…”

“…Previously, we and others demonstrated the involvement of F. graminearum FgSTE2 and FgSTE3 GPCRS in fungal hyphal chemotropism toward the product of a catalytic reaction conducted by host-released peroxidases (Sharma et al, 2022a;Sridhar et al, 2020;Turrà et al, 2015). ΔFgSte2 and ΔFgSte3 deletion strains each individually lead to complete elimination of the chemotropic response to horse radish peroxidase (HRP).…”