Fusarium oxysporum cell wall proteome under adhesion-inducing conditions

Fusarium oxysporum is a soilborne fungus that causes vascular wilt disease on a wide range of crops. During initial stages of infection, fungal hyphae attach firmly to roots, penetrate the cortex and colonize xylem vessels. The mechanisms underlying root attachment are poorly understood, although it was previously shown that this process depends on Fmk1, a mitogen-activated protein kinase orthologous to the mating/filamentation mitogen-activated protein kinases Fus3/Kss1 in yeast. We investigated the hypothesis that root adhesion is mediated by fungal cell wall proteins (CWPs). To characterize the cell wall subproteome of F. oxysporum, we performed LC-MS/MS analysis of tryptic digests of purified cell walls obtained from adhesion-inducing conditions, identifying a total of 174 proteins, 19 of which contain a predicted signal peptide and 10 of which have a predicted glycosylphosphatidyl-inositol motif. 2-D DIGE was used to compare four different fractions of CWPs extracted from hyphae of the wild-type strain and the Δfmk1 mutant. We detected 18 proteins differing significantly in abundance between the two strains. Differential expression of five of these proteins was confirmed by RT-PCR analysis. A significant fraction of the subproteome lacked functional information, highlighting the limitations in the current understanding of CWPs in F. oxysporum.