Rho1 has distinct functions in morphogenesis, cell wall biosynthesis and virulence of Fusarium oxysporum

Abstract

SummaryRho-type GTPases regulate polarized growth in yeast by reorganization of the actin cytoskeleton and through signalling pathways that control the expression of cell wall biosynthetic genes. We report the cloning and functional analysis of rho1 from Fusarium oxysporum, a soilborne fungal pathogen causing vascular wilt on plants and opportunistic infections in humans. F. oxysporum strains carrying either a Drho1 loss-of-function mutation or a rho1 G14V gain-offunction allele were viable, but displayed a severely restricted colony phenotype which was partially relieved by the osmotic stabilizer sorbitol, indicating structural alterations in the cell wall. Consistent with this hypothesis, Drho1 strains showed increased resistance to cell wall-degrading enzymes and staining with Calcofluor white, as well as changes in chitin and glucan synthase gene expression and enzymatic activity. Re-introduction of a functional rho1 allele into the Drho1 mutant fully restored the wild-type phenotype. The Drho1 strain had dramatically reduced virulence on tomato plants, but was as virulent as the wild type on immunodepressed mice. Thus, Rho1 plays a key role during fungal infection of plants, but not of mammalian hosts.

Ustilago maydis Rho1 and 14-3-3 Homologues Participate in Pathways Controlling Cell Separation and Cell Polarity

“…In yeast and F. oxysporum, Rho1 has been suspected to play a crucial role in modulating the activity of chitin synthase, a core component of the cell wall biosynthesis machinery (30,42). A rho1-null F. oxysporum is incapable of maintaining hyphal growth on solid medium (30). In mammalian systems, Rho/Rac-GTPases regulate lamellae formation.…”

“…For example, Rac1 has been shown to regulate cell polarity, while Cdc42 regulates cytokinesis in U. maydis (29). In yeast and F. oxysporum, Rho1 has been suspected to play a crucial role in modulating the activity of chitin synthase, a core component of the cell wall biosynthesis machinery (30,42). A rho1-null F. oxysporum is incapable of maintaining hyphal growth on solid medium (30).…”

“…14-3-3 functions have been associated with filamentous or pseudohyphal growth in C. albicans (37) and Yarrowia lipolytica. In C. albicans (30) and Y. lipolytica (16), strains with mutations in 14-3-3 proteins either develop abnormal filaments or fail to differentiate completely. To determine whether Pdc1 has any effect on aerial hyphae formation, we used pdc1 nar1 in otherwise wildtype-compatible mating types.…”

Comparative genomics of MAP kinase and calcium–calcineurin signalling components in plant and human pathogenic fungi

“…Similar to S. cerevisiae, Rho1 is required for cell viability in C. albicans (Smith et al, 2002). In contrast, rho1 knockout mutants of the soilborne pathogen Fusarium oxysporum were viable and showed drastically reduced virulence on plants, but retained full virulence on immunodepressed mice (Martinez-Rocha et al, 2008). Both Rom1 and 2, as well as Rho1, are widely conserved in fungi, with a single orthologue of the two GEFs present in almost all species studied.…”

Peroxicretion, a Novel Tool for Engineering Membrane Trafficking

“…In addition, the identification of the small GTPase Rho1p as being localized on peroxisomes by interaction of the peroxisomal membrane protein Pex25p again indicates a link of peroxisomes with the secretory machinery 61 , since Rho1p is known to play a role in actin reorganization and membrane dynamics 62,63 . In yeast, polarized growth is regulated by Rho1p 64 , and also in fungal systems the link between Rho1 and polarized growth has been confirmed 65 in the filamentous fungus A. niger, polarized growth is linked to secretion of proteins 66 . More recent papers also very clearly showed that peroxisomes originate from the endoplasmic reticulum 60,67,[68][69][70] .…”