Biology subjects

Ibeas, J. I.

Publications and source records attributed to Ibeas, J. I..

5 recordsLinked to original sources

bioRxiv2026

Glu1, a conserved GH30_3 β-(1,6)-glucanase requires its catalytic residues for full virulence in Ustilago maydis

Plant-pathogenic fungi cause plant diseases and severe agricultural losses. The fungal cell wall is the first point of contact and defense barrier between fungus and host, maintaining cellular integrity and structural stability but also playing a dynamic role during infection. Through pathogenic development, the fungal cell wall must be continuously remodelled to accommodate morphological transitions and environmental challenges through diverse cell wall modifying enzymes necessary for successful infection. Here, we characterise Glu1, a putative endo-{beta}-(1,6)-glucanase (GH30) from the maize pathogen Ustilago maydis, conserved across Ustilaginales. Structural comparison with characterised GH30 crystal structures shows Glu1 most closely resembles GH30_3 {beta}-(1,6)-glucanases. Glu1 expression is induced during infection, localises to the plasma membrane in close association with the fungal cell wall and is detected in the secreted fraction. Deletion of glu1 reduces virulence, impairs plant colonization and tumour formation, and alters septation and cell morphology under saprophytic growth. Notably, genetic rescue with Glu1 catalytic-site variants largely restores saprophytic phenotypes but not virulence, suggesting a catalytic-dependent function of Glu1 specifically required for infection. Umag_04357, the other GH30 enzyme identified in U. maydis, reveals a conserved GH30 domain, including the catalytic residues, but is expressed at lower levels during infection and its deletion does not affect virulence. Together, our findings indicate that Glu1 is a conserved GH30 enzyme with a {beta}-(1,6)-glucanase-like pocket whose catalytic residues are required for full virulence. To our knowledge, it is the first GH30 enzyme linked to virulence in Basidiomycota and could be considered a potential target for smut disease control.

molecular biology↗

bioRxiv2026

Perinuclear anchoring of telomeres enables plant infection by Ustilago maydis

The spatial organization of the genome is critical for cellular function, yet its contribution to the success of host-pathogen interactions remains poorly understood. A conserved hallmark of nuclear architecture is the perinuclear localization of heterochromatin, which includes not only specific chromosomal subdomains but also major structural elements like centromeres and telomeres. To determine the importance of this organization during fungal pathogenesis, we used the maize pathogen Ustilago maydis as an infection model system. We identify the lamina-associated protein homolog, Lem2, as a molecular tether for telomeres and show its deletion abrogates fungal penetration, causing developmental arrest at the appressorium stage. Mechanistically, this infection defect is associated with a failure in nuclear migration. Using hyphal filaments induced under axenic conditions, we observed that mutant nuclei consistently fail to transit from the mother cell into the growing filament. Furthermore, RNA-seq analysis correlates this failure with a marked misregulation of the DNA damage response (DDR) and cell cycle control, including the aberrant expression of multiple checkpoint and signaling proteins. Crucially, artificially tethering telomeres to the nuclear periphery in this mutant partially restores the nuclear migration defect and plant penetration, while simultaneously suppressing the aberrant DDR. This work establishes a functional link between a specific spatial nuclear configuration and fungal infectivity, revealing the conserved telomere-anchoring machinery as a potential target for novel antifungal strategies.

molecular biology↗

bioRxiv2023

Row1, a member of a new family of conserved fungal proteins involved in infection, is required for appressoria functionality in Ustilago maydis

The appressorium of phytopathogenic fungi is a specific structure with a crucial role in plant cuticle penetration. Pathogens with melanized appressoria break the cuticle through cell wall melanization and intracellular turgor pressure. However, in fungi with non-melanized appressorium, the mechanisms governing cuticle penetration are poorly understood. Here we characterize Row1, a previously uncharacterized appressoria-specific protein of Ustilago maydis that localizes to membrane and secretory vesicles. Deletion of row1 decrease appressoria formation and plant penetration, thereby reducing virulence. Specifically, the {Delta}row1 mutant has a thicker cell wall that is more resistant to glucanase degradation. We also observed that the {Delta}row1 mutant has secretion defects. Our data suggest that Row1 could modify the glucans that form the fungal cell wall and may be involved in unconventional protein secretion, thereby promoting both appressoria maturation and penetration. We show that Row1 is functionally conserved at least among Ustilaginaceae and belongs to the Row family, which consists of five other proteins that are highly conserved among Basidiomycota fungi and are involved in U. maydis virulence. We observed similarities in localization between Row1 and Row2, which is also involved in cell wall remodelling and secretion, suggesting similar molecular functions for members of this protein family.

microbiology↗

bioRxiv2023

Systematic characterization of Ustilago maydis sirtuins shows Sir2 as a modulator of pathogenic gene expression

Phytopathogenic fungi must adapt to the different environmental conditions found during infection and avoid the immune response of the plant. For these adaptations, fungi must tightly control gene expression, allowing sequential changes in transcriptional programs. In addition to transcription factors, chromatin modification is used by eukaryotic cells as a different layer of transcriptional control. Specifically, the acetylation of histones is one of the chromatin modifications with a strong impact on gene expression. Hyperacetylated regions usually correlate with high transcription and hypoacetylated areas with low transcription. Thus, histone deacetylases (HDACs) commonly act as repressors of transcription. One member of the family of HDACs is represented by sirtuins, which are deacetylases dependent on NAD+, and, thus, their activity is considered to be related to the physiological stage of the cells. This property makes sirtuins good regulators during environmental changes. However, only a few examples exist, and with differences in the extent of the implication of the role of sirtuins during fungal phytopathogenesis. In this work, we have performed a systematic study of sirtuins in the maize pathogen Ustilago maydis, finding Sir2 to be involved in the dimorphic switch from yeast cell to filament and pathogenic development. Specifically, the deletion of sir2 promotes filamentation, whereas its overexpression highly reduces tumor formation in the plant. Moreover, transcriptomic analysis revealed that Sir2 represses genes that are expressed during biotrophism development. Interestingly, our results suggest that this repressive effect is not through histone deacetylation, indicating a different target of Sir2 in this fungus.

molecular biology↗

bioRxiv2019

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

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 a crucial event for pathogenic development in U. maydis. Our results provide new insights into the role of glycosylation in fungal pathogenesis.\n\nAuthor summaryFungal pathogens require virulence factors to be properly secreted and localized to guarantee complete infection. In common with many proteins, virulence factors must be post-translationally modified by glycosylation for normal localization, secretion and function. This is especially important for virulence factors, which are mainly comprised of cell wall and secreted proteins. Aberrant glycosylation leads to a loss of virulence in both animal and plant pathogenic fungi. We have previously demonstrated that glycosylation is important for virulence of the corn smut fungus, Ustilago maydis. However, the glycoproteins involved and their specific roles in the infection process have not yet been reported. Here, we describe a proteomic assay designed to identify glycoproteins involved in plant infection. Using this method, we define the role of Pdi1 protein disulfide isomerase in virulence. Interestingly, abolishing Pdi1 N-glycosylation mimics {Delta}pdi1 defects observed during infection, suggesting that Pdi1 N-glycosylation is required for the secretion of virulence factors. We hypothesize that Pdi1 N-glycosylation is crucial for maintaining proper effector protein folding during the infection process, especially in the harsh conditions found inside the maize plant.

microbiology↗