N-glycosylation of the protein disulfide isomerase Pdi1 ensures full Ustilago maydis virulence

Abstract

Fungal pathogenesis depends on accurate secretion and location of virulence factors which drive host colonization. Protein glycosylation is a common posttranslational modification of cell wall components and other secreted factors, typically required for correct protein localization, secretion and function. Thus, the absence of glycosylation is associated with animal and plant pathogen avirulence. While the relevance of protein glycosylation for pathogenesis has been well established, the main glycoproteins responsible for the loss of virulence observed in glycosylation-defective fungi have not been identified. Here, we devise a proteomics approach to identify such proteins and use it to demonstrate a role for the highly conserved protein disulfide isomerase Pdi1 in virulence. We show that efficient Pdi1 N-glycosylation, which promotes folding into the correct protein conformation, is required for full pathogenic development of the corn smut fungus Ustilago maydis. Remarkably, the observed virulence defects are reminiscent of those seen in glycosylation-defective cells suggesting that the N-glycosylation of Pdi1 is necessary for the full secretion of virulence factors. All these observations, together with the fact that Pdi1 protein and RNA expression levels rise upon virulence program induction, suggest that Pdi1 glycosylation is important for normal pathogenic development in U. maydis. Our results provide new insights into the role of glycosylation in fungal pathogenesis.

Comparative Transcriptomics and RNA-Seq-Based Bulked Segregant Analysis Reveals Genomic Basis Underlying Cronartium ribicola vcr2 Virulence

“…PDO and PDI are key players for enzymatic disulfide bond reduction, oxidation and isomerization, contributing to essential steps in the protein folding pathway and to the stability of the native state of the proteins ( Ladenstein and Ren, 2006 ). PDI-1 assists a set of glycoproteins in folding and disulfide bonds formation during effector secretion into the apoplast of maize plants during Ustilago maydis infection and its deletion led to a strong reduction in virulence ( Marín-Menguian et al, 2019 ).…”

Comparative secretome ofMagnaporthe oryzaeidentified proteins involved in virulence and cell wall integrity

“…Mutants of protein N -glycosylation showing defected in fungal virulence are reported not only for M. oryzae [45], but also for other plant pathogens such as Penicilium digitatum, Botrytis cinerea and Ustilago maydis [24, 25, 46-52]. Recent study on glycoprotein proteomics in Ustilago maydis using wildtype and mutants Δ gls1 , a mutant also involved in N -glycosylation process, had identified several protein with N -glycosylation modification [53]. In our study, comparing the secretome of P131 and Δ alg3 , 17 proteins were totally absent in the Δ alg3 strain and 34 proteins had a significantly higher abundance in P131 samples than in Δ alg3 samples; thus, these 51 proteins were considered secreted proteins that specifically require ALG3 for their secretion (Table 3).…”

Protein glycosylation during infection by plant pathogenic fungi

“…1). N‐ glycosylation of Pdi1 affects its electrophoretic mobility, but not cellular location or stability (Marín‐Menguiano et al ., 2019). GPI anchoring may also be necessary for the function of some effector proteins (Fig.…”