Abstract:　The　E3　ubiquitin　ligase　Ubr1　is　a　core　player　in　yeast　ubiquitylation　and　protein　quality　control　required　for　cellular　events　including　proteasomal　degradation　and　gene　activity　but　has　been　rarely　explored　in　filamentous　fungi.　We　show　here　an　essentiality　of　orthologous　Ubr1-mediated　ubiquitylation　for　the　activation　of　central　developmental　pathway　(CPD)　and　the　CPD-controlled　cellular　events　in　Beauveria　bassiana,　a　filamentous　fungal　insect　pathogen　that　undergoes　an　asexual　cycle　in　vitro　or　in　vivo.　As　a　result　of　ubr1　disruption,　intracellular　free　ubiquitin　accumulation　increased　by　1.4-fold,　indicating　an　impaired　ability　for　the　disruptant　to　transfer　ubiquitin　to　target　proteins.　Consequently,　the　disruptant　was　compromised　in　polar　growth　featured　with　curved　or　hook-like　germ　tubes　and　abnormally　branched　hyphae,　leading　to　impeded　propagation　of　aberrant　hyphal　bodies　in　infected　insect　hemocoel　and　attenuated　virulence.　In　the　mutant,　sharply　repressed　expression　of　three　CDP　activator　genes　(brlA,　abaA,　and　wetA)　correlated　well　with　severe　defects　in　aerial　conidiation　and　submerged　blastospore　(hyphal　body)　production　in　insect　hemolymph　or　a　mimicking　medium.　Moreover,　the　disruptant　was　sensitive　to　cell　wall　perturbation　or　lysing　and　showed　increased　catalase　activity　and　resistance　to　hydrogen　peroxide　despite　null　response　to　high　osmolarity　or　heat　shock.　Most　of　the　examined　genes　involved　in　polar　growth　and　cell　wall　integrity　were　down-regulated　in　the　disruptant.　These　findings　uncover　that　the　Ubr1-mediated　ubiquitylation　orchestrates　polar　growth　and　the　CDP-regulated　asexual　cycle　in　vitro　and　in　vivo　in　B.　bassiana.　Key　points:　•　Ubr1　is　an　E3　ubiquitin　ligase　essential　for　ubiquitylation　in　Beauveria　bassiana.　•　Ubr1-mediated　ubiquitylation　is　required　for　activation　of　central　development　pathway.　•　Ubr1　orchestrates　polar　growth　and　asexual　cycle　in　vitro　and　in　vivo.　©　2021,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.