Biology subjects

Tzelepis, G.

Publications and source records attributed to Tzelepis, G..

4 recordsLinked to original sources

bioRxiv2026

Functional and transcriptomic analyses in Neurospora crassa reveal the crucial role of N-glycoprotein deglycosylation process in fungal homeostasis.

N-glycosylation is an essential post-translational modification required for proper protein folding, stability, trafficking, and secretion in eukaryotes. In such organisms, an efficient endoplasmic reticulum (ER) quality control, such as the ER-associated degradation (ERAD) pathway, is critical for maintaining cellular homeostasis. During ERAD, terminally misfolded glycoproteins undergo N-deglycosylation prior to proteasomal degradation, a process typically mediated by peptide N-glycanase (PNGase). However, in the filamentous fungi, the PNGase seems to be catalytically inactive, indicating evolutionary divergence from the canonical PNGase pathway. Filamentous fungi also encode endo-{beta}-N-acetylglucosaminidases (ENGases), particularly members of glycoside hydrolase family 18 (GH18), which may compensate for the loss of canonical PNGase activity. Here, we investigated the roles of the cytosolic GH18 ENGase and a putative acidic PNGase in N. crassa using transcriptomic and functional approaches. Our results demonstrate that the cytosolic GH18 ENGase is an active deglycosylating enzyme likely associated with the ERAD pathway, whereas no deglycosylation activity was detected for the acidic PNGase. Deletion of the ENGase severely compromises tolerance to diverse stress conditions and induces substantial transcriptomic reprogramming, including upregulation of a GH20 exo-{beta}-N-acetylhexosaminidase under ER stress. These findings identify cytosolic ENGase as a key component of fungal proteostasis and suggest that N. crassa activates alternative compensatory mechanisms to maintain protein quality control when canonical deglycosylation pathways are impaired.

microbiology↗

bioRxiv2024

SREBP-mediated gene expression regulation is essential for the intrinsic fungicide tolerance and antagonism in the fungal biocontrol agent Clonostachys rosea

Sterol regulatory element-binding proteins (SREBPs) are a family of transcription factors known to regulate sterol biosynthesis and homeostasis in fungi. For this reason they have a role in several biological processes, including virulence, fungicide tolerance, hypoxia adaptation, lipid and carbohydrate metabolisms, and iron homeostasis. While the biological function of SREBPs in yeast and filamentous fungal species pathogenic to humans and plants is known, their role in fungal biocontrol agents (BCAs) is still elusive. This study aimed to investigate the biological and regulatory function of SREBPs in the BCA Clonostachys rosea, with a focus on their role in fungicide tolerance, hypoxia adaptation and antagonisms. The C. rosea genome contains two genes (sre1 and sre2) coding for SREBPs and one gene each coding for Insulin induced gene (INSIG) and SREBP cleavage-activating protein (SCAP), required for SREBP-mediated ergosterol biosynthesis in fungi. Deletion of sre1 resulted in mutants with pleiotropic effects, including the reduced ability to grow on media supplemented with proline (active ingredient prothioconazole) and cantus (active ingredient boscalid) fungicides, hypoxia mimicking agent CoCl2, cell wall stressor SDS, and increased growth rate on medium supplemented with caffeine, compared with C. rosea wild type (WT). In addition, the antagonistic ability against the fungal hosts Botrytis cinerea and Rhizoctonia solani was affected when sre1 was deleted. However, no significant difference between sre2 deletion strains and C. rosea WT was found for any of the tested phenotypes. To investigate the regulatory role of SRE1, the transcriptome of C. rosea WT and a sre1 deletion strain was analyzed. The transcriptome analysis identified differentially expressed genes in the sre1 deletion strain associated with carbohydrate and lipid metabolism, respiration, iron homeostasis, and xenobiotic tolerance. Moreover, genes coding for polyketide synthases and chitinases with a proven antimicrobial role were downregulated in the mutant, corroborating the reduced antagonism phenotypes. In summary, this work sheds light on the regulation role of transcription factor SRE1 while also exploring its effect on regulating the antagonistic activity and fungicide resistance of C. rosea, giving us helpful knowledge to design applications of this organism in IPM strategies.

microbiology↗

bioRxiv2022

The phospholipase VlsPLA2 from the plant pathogen Verticillium longisporum is a virulence factor targeting host nuclei and suppressing PTI-related hypersensitive response

Phospholipases A2 (PLA2) are lipolytic enzymes, responsible for phospholipids hydrolysis. The role of PLA2 in various aspects of cell physiology has been shown, but their involvement in host-microbe interactions remains to be elucidated. The present study investigated the biological function of the secreted VIsPLA2 phospholipase in the phytopathogenic fungus Verticillium longisporum with emphasis on its role in host-microbe interactions. The VlsPLA2 was highly induced in V. longisporum during interaction with host plant Brassica napus, encoding an active phospholipase A2. VlsPLA2-overexpression V. longisporum strain showed an increased virulence on Arabidopsis plants, plausibly by inducing virulence factors. Furthermore, VIsPLA2 are transported to the nucleus, by hijacking VAMPA proteins, causing suppression of PTI-induced hypersensitive response, possibly by modulating the expression of genes involved in plant immunity. In summary, VlsPLA2 acts as a virulence factor by hydrolyzing the hosts nuclear envelope phospholipids, an action that induces signaling cascade, suppressing basal plant immunity responses.

microbiology↗

bioRxiv2018

The Rhizoctonia solani LysM and RlpA-like effector proteins contribute to virulence suppressing chitin-triggered immunity and hypersensitive response

Rhizoctonia (in Greek \"root-killer\") species and particularly R. solani attacks a broad range of plant species and crops. It belongs to Basidiomycota and is a soil-borne pathogen causing mainly damping-off diseases of seedlings and root rot, although it can infect plants in any stage. Despite the severity of this disease, many aspects in R. solani infection biology still remain to be elucidated. Here we investigated the role of two effector candidates, predicted from the genome of a R. solani AG2-2IIIB strain that uses sugar beet as a host. Gene expression analysis showed that genes encoding for a LysM effector and a rare lipoprotein-A-like protein (RsRlpA) were induced upon early infection stages. When heterologous expressed in Cercospora beticola the two genes contributed to virulence. The RsLysM effector showed chitin- binding affinity and suppression of chitin-triggered immunity but could not protect hyphae from hydrolysis. The RsRlpA effector suppressed hypersensitive response in Nicotiana benthamiana leaves. Overall, this study provides us with valuable information on R. solani infection biology, implying that this organism relies on mechanisms similar to hemibiotrophic pathogens in order to establish a successful infection.

plant biology↗