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F-box proteins determine substrate specificity of the ubiquitin-proteasome system. Previous work has demonstrated that the F-box protein Fbp1, a component of the SCF(Fbp1) E3 ligase complex, is essential for invasive growth and virulence of the fungal plant pathogen Fusarium oxysporum. Here, we show that, in addition to invasive growth, Fbp1 also contributes to vegetative hyphal fusion and fungal adhesion to tomato roots. All of these functions have been shown previously to require the mitogen-activated protein kinase (MAPK) Fmk1. We found that Fbp1 is required for full phosphorylation of Fmk1, indicating that Fbp1 regulates virulence and invasive growth via the Fmk1 pathway. Moreover, the Δfbp1 mutant is hypersensitive to sodium dodecylsulfate (SDS) and calcofluor white (CFW) and shows reduced phosphorylation levels of the cell wall integrity MAPK Mpk1 after SDS treatment. Collectively, these results suggest that Fbp1 contributes to both the invasive growth and cell wall integrity MAPK pathways of F. oxysporum., (© 2015 BSPP AND JOHN WILEY & SONS LTD.)

Like many hemibiotrophic plant pathogens, the root-infecting vascular wilt fungus Fusarium oxysporum induces an increase in the pH of the surrounding host tissue. How alkalinization promotes fungal infection is not fully understood, but recent studies point towards the role of cytosolic pH (pHc) and mitogen-activated protein kinase (MAPK) signaling. In fungi, pHc is mainly controlled by the essential plasma membrane H+-ATPase Pma1. Here we created mutants of F. oxysporum lacking casein kinase 1 (Ck1), a known negative regulator of Pma1. We found that the ck1Δ mutants have constitutively high Pma1 activity and exhibit reduced alkalinization of the surrounding medium as well as decreased hyphal growth and conidiation. Importantly, the ck1Δ mutants exhibit defects in hyphal chemotropism towards plant roots and in pathogenicity on tomato plants. Thus, Ck1 is a key regulator of the development and virulence of F. oxysporum. [ABSTRACT FROM AUTHOR]