Colletotrichum orbiculare FAM1 Encodes a Novel Woronin Body-Associated Pex22 Peroxin Required for Appressorium-Mediated Plant Infection

Abstract

The cucumber anthracnose fungus Colletotrichum orbiculare forms specialized cells called appressoria for host penetration. We identified a gene, FAM1, encoding a novel peroxin protein that is essential for peroxisome biogenesis and that associates with Woronin bodies (WBs), dense-core vesicles found only in filamentous ascomycete fungi which function to maintain cellular integrity. The fam1 disrupted mutants were unable to grow on medium containing oleic acids as the sole carbon source and were nonpathogenic, being defective in both appressorium melanization and host penetration. Fluorescent proteins carrying peroxisomal targeting signals (PTSs) were not imported into the peroxisomes of fam1 mutants, suggesting that FAM1 is a novel peroxisomal biogenesis gene (peroxin). FAM1 did not show significant homology to any Saccharomyces cerevisiae peroxins but resembled conserved filamentous ascomycete-specific Pex22-like proteins which contain a predicted Pex4-binding site and are potentially involved in recycling PTS receptors from peroxisomes to the cytosol. C. orbiculare FAM1 complemented the peroxisomal matrix protein import defect of the S. cerevisiae pex22 mutant. Confocal microscopy of Fam1-GFP (green fluorescent protein) fusion proteins and immunoelectron microscopy with anti-Fam1 antibodies showed that Fam1 localized to nascent WBs budding from peroxisomes and mature WBs. Association of Fam1 with WBs was confirmed by colocalization with WB matrix protein CoHex1 (C. orbiculare Hex1) and WB membrane protein CoWsc (C. orbiculare Wsc) and by subcellular fractionation and Western blotting with antibodies to Fam1 and CoHex1. In WB-deficient cohex1 mutants, Fam1 was redirected to the peroxisome membrane. Our results show that Fam1 is a WB-associated peroxin required for pathogenesis and raise the possibility that localized receptor recycling occurs in WBs.

MrHex1 is Required for Woronin Body Formation, Fungal Development and Virulence in Metarhizium robertsii

“…Both the deletion and overexpression of FgHex1 in F. graminearum reduced fungal infectivity [ 19 ]. However, intriguingly, the deletion of CoHex1 in the cucumber anthracnose fungus Colletotrichum orbiculare did not produce any detectable defects in appressorium formation and infectivity [ 42 ]. This kind of species-dependent phenotypic diversity of Hex1 deletion mutants indicates again the functional alterations of this conserved gene in different fungi.…”

Pex13 and Pex14, the key components of the peroxisomal docking complex, are required for peroxisome formation, host infection and pathogenicity-related morphogenesis inMagnaporthe oryzae

“…Notably, filamentous ascomycetes have a specific peroxin, Pex22-like, which shows low homology to Pex22 in S. cerevisiae but contains a typical Pex4-binding domain conserved in Pex22 proteins [27]. Fam1, the Pex22-like protein in C. orbiculare, has been shown to be able to complement the defect in peroxisomal matrix import of S. cerevisiae pex22 mutants [57]. fam1 mutants are incapable of importing PTS-containing proteins and are defective in peroxisome function and pathogenicity.…”

Twinfilin regulates actin assembly and Hexagonal peroxisome 1 (Hex1) localization in the pathogenesis of rice blast fungus Magnaporthe oryzae

“…In M. oryzae , deletion of Hex1 showed that WBs are required not only for appressorial morphogenesis but also for invasive growth in plants by enhancing resistance to nutritional stress (Soundararajan et al, 2004 ). WBs are distributed at the hyphal tips and septa (Kubo et al, 2015 ). Currently, we do not know the significance of the hyphal tip‐localized WBs and the mechanism of how WBs are distributed at the hyphal tip.…”

“…WBs are distributed at the hyphal tips and septa (Kubo et al, 2015). Currently, we do not know the significance of the hyphal tip-localized WBs and the mechanism of how WBs are distributed at the hyphal tip.…”