The coiled-coil protein-binding motif in Fusarium verticillioides Fsr1 is essential for maize stalk rot virulence

Abstract

Fusarium verticillioides (Sacc.) Nirenberg (teleomorph Gibberella moniliformis Wineland) is one of the key pathogens of maize stalk rot disease. However, a clear understanding of stalk rot pathogenesis is still lacking. Previously, we identified the F. verticillioides FSR1 gene, which plays a key role in fungal virulence and sexual mating. The predicted Fsr1 protein contains multiple protein-binding domains, namely a caveolin-binding domain, a coiled-coil structure, and a calmodulin-binding motif at the N terminus and a WD40 repeat domain at the C terminus. Fsr1 shares significant similarity to a family of striatin proteins that play a critical role in cellular mechanisms that regulate a variety of developmental processes. Significantly, FSR1 function is conserved in Fusarium graminearum, where it also plays a direct role in pathogenesis. In this study, our goal was to determine the motif(s) in Fsr1 that are directly associated with fungal virulence. We complemented the FSR1 knockout (Dfsr1) strain with mutated versions of the FSR1 gene, and determined that the Fsr1 C-terminal WD40 repeat domain is dispensable for vegetative growth and maize stalk rot virulence. We also examined the potential link between FSR1-mediated virulence and cell wall-degrading enzyme (a-amylase, pectinase and cellulase) activities. Further characterization of the N-terminal region revealed that the coiled-coil structure is essential for virulence in F. verticillioides. The coiled-coil domain is involved in a variety of protein-protein interactions in eukaryotic systems, and thus we hypothesize that the interaction between Fsr1 and the putative Fsr1-binding protein triggers downstream gene signalling that is associated with F. verticillioides virulence.

RNAi-induced silencing of an effector confers transcriptional oscillation in another group of effectors in the root-knot nematode, Meloidogyne incognita

“…In line with the revelation by Yamamura & Shim (2008) in fungal pathogens, we have shown the possible link between pioneer gene-mediated M. incognita pathogenesis and CWDE activities using RNAi, which is perhaps the only effective technique to study gene manipulation in plant-parasitic nematodes. Remarkably, our experiments revealed that induced suppression of one parasitism gene may cause overexpression or suppression of another group of parasitism genes.…”

“…Therefore, characterisation of the individual and integrative function of different nematode effectors is required for deeper understanding of plant-nematode interaction, which is as yet an underexplored territory. Interestingly, Yamamura & Shim (2008) showed that the coiled-coil domain of FSR1 gene plays a key role in the pathogenicity of the fungi, Fusarium verticillioides. Along with that, a potential link between FSR1-mediated virulence and activity of the fungal CWDEs (α-amylase, pectinase and cellulase) was also established.…”

STRIPAK complexes: Structure, biological function, and involvement in human diseases

“…F. verticillioides defective for Fsr1 display reduced radial growth on agar, fewer aerial mycelia, and inability to penetrate and grow in maize stalk in a stalk-rot assay (Shim et al, 2006, Yamamura and Shim, 2008). While Fsr1 is not critical for male fertility in F. verticillioides , it is required for female fertility and the development of perithecia (Shim et al, 2006).…”

“…Similarly, deletion of Fsr1 in F. graminearu also leads to a block in perithecia development and significantly reduced head blight symptoms of this fungus on barley (Shim et al, 2006). In F. verticillioides , the growth and virulence defects of a ΔFsr1 strain could be rescued by expression of an Fsr1 mutant lacking the WD-repeat domain or by expression of a mutant lacking both the WD-repeat domain and the caveolin-binding domain (Yamamura and Shim, 2008). Given the importance of the WD-repeats for Mob3 binding in mammalian cells (Gordon et al, 2011), it will be interesting to determine if the F. verticillioides Mob3 homolog is dispensable for virulence.…”

“…Also of note, caveolins do not appear to be expressed in fungi (Field et al, 2007) and some of the fungal striatin homologs lack a full consensus caveolin-binding domain (Couet et al, 1997); thus, the function of this stretch of amino acids in fungal striatin homologs is currently unclear. Interestingly, the growth and virulence defects of the ΔFsr1 strain could not be rescued by expression of a mutant lacking both the WD-repeat domain and the coiled-coil domain (Yamamura and Shim, 2008). Thus, at least in the absence of the WD-repeat domain, the coiled-coil domain is required for normal growth and virulence, while the WD-repeat domain appears to be dispensable for both.…”