Ubiquitin is a posttranslational modifier that is conserved among eukaryotes. Ubiquitination alters stability and folding of cellular proteins. Deubiquitinases (DUBs) reverse ubiquitination and often function as part of protein complexes. There are 32 predicted DUB-encoding genes present in the soil-borne phytopathogenic fungus Verticillium dahliae. Nuclear ubiquitin-specific protease 3 (Usp3) is a member of the Spt-Ada-Gcn5 acetyltransferase (SAGA) complex, whereas Usp1 is predicted to associate with the COP9 signalosome (CSN), which controls specificities of cellular E3 ubiquitin ligase activities. A proteomics approach using biotin capture and identification (BioID) supports that Usp3 regulates gene expression beyond the transcription level. Western experiments showed a dysregulation in ubiquitinated cellular proteins in corresponding deletion strains. Usp3 and Usp1 are both required for fungal development. They regulate microsclerotia formation based on different environmental cues and provide redundant functions in controlling conidiation. Absence of both corresponding genes resulted in significant impairment of conidiospore formation, which is required for fungal propagation within the plant vascular system. This paralysed spreading ability reduced virulence on tomato plants (Solanum lycopersicum). In summary, V. dahliae responds to environmental cues by Usp3- and Usp1-mediated adjustment of gene expression and protein stability. This is important for key developmental processes of the V. dahliae disease cycle and its virulence towards the host plant.
Chen, Y.-Y., Leonard, M., Kocatürk, M., Assmann, N. F., Bromm, M., Aden, M., Schmitt, K., Valerius, O., Harting, R., Braus, G. H.
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